Journal Logo

Epidemiology

Resistance training combined with bench-step aerobics enhances women’s health profile

KRAEMER, WILLIAM J.; KEUNING, MONICA; RATAMESS, NICHOLAS A.; VOLEK, JEFF S.; McCORMICK, MATHEW; BUSH, JILL A.; NINDL, BRADLEY C.; GORDON, SCOTT E.; MAZZETTI, SCOTT A.; NEWTON, ROBERT U.; GÓMEZ, ANA L.; WICKHAM, ROBBIN B.; RUBIN, MARTYN R.; HÄKKINEN, KEIJO

Author Information
Medicine and Science in Sports and Exercise: February 2001 - Volume 33 - Issue 2 - p 259-269
  • Free

Abstract

With the importance of exercise training a crucial factor in women’s health issues, there is a need for training studies that examine popular forms of exercise used by many women today. Bench-step aerobics (BSA) has grown dramatically since the late 1980s and has been primarily focused on developing cardiovascular fitness and improved body composition profiles (29). To date, no studies have attempted to add a resistance training component to a BSA program to enhance muscle strength and power, which are also vital aspects for women’s health (e.g., aging, prevention of falls, bone health, and performance). BSA involves choreographed, rhythmical movements on a step performed to cadenced musical arrangements (8). Previous investigations have shown significant acute cardiovascular and metabolic demands with BSA especially in individuals with high lean body mass, body weight, and leg length (29,32) and with the addition of larger steps (26), more complex movements, hand weights (26), and faster stepping rates (29,32). Chronic adaptations to BSA appear comparable to other forms of aerobic exercise (29,30). Whereas improvements in cardiorespiratory fitness and body fat reduction have been observed with BSA (17,29), less is known concerning the effects of BSA on muscular performance (i.e., strength, power, and local muscular endurance). In one study, Koenig et al. (17) reported an insignificant increase in local muscular endurance after 10 wk of BSA. Interestingly, muscular strength decreased significantly, whereas no differences in power were observed (17). Although a popular form of exercise, surprisingly few data exist regarding its physiological and performance adaptations, thus creating a distinct need for research in this area of study.

It is well known that resistance training can improve muscular strength, local muscular endurance, and power and stimulate positive effects on body composition (e.g., decrease in percent fat) (23,33,34). We hypothesized that the addition of a resistance training program to BSA would enhance the total physical fitness profile of women to also include lean tissue mass, strength, and power measures (13). Considering the limitations in muscular strength development observed with BSA alone, we also hypothesized that addition of a resistance exercise component to a BSA program would enhance muscular fitness, especially in the upper body, which is a primary target for strength training in women (7). However, to optimize the time component, both types of exercise protocols may have to be performed within the same training period. This would necessitate a reduction in the normal amount of time typically given to BSA. However, since resistance training has been shown to enhance aerobic capacity in untrained women (23), we hypothesized that the time spent on resistance exercise would actually further enhance the aerobic capacity in previously untrained women while adding neuromuscular fitness components to the program’s adaptations (13).

With the use of both forms of exercise training, another important consideration for any combined exercise program was the compatibility of simultaneous strength and endurance training. Because the adaptive responses to strength and endurance training are different and may be opposite in their adaptive stimuli (22), it has been proposed that skeletal muscle may not optimally adapt to the two training stimuli when they are simultaneously imposed at high intensities (22,28). Investigations comparing resistance training versus the combination of both resistance and endurance training have reported both impaired strength (4,11,12) and power (22) enhancement with no limitations on improvements of maximal aerobic power or short-term endurance (4,11,12). Thus, it appears that power and the rate of strength development are most susceptible to the antagonistic effects of combined strength and endurance training (22). However, if both programs are performed with adequate days of rest between training sessions, it was theorized that incompatibility would not be a problem in women performing both types of exercise training programs (23,35).

The purpose of this study was to investigate the comprehensive physiological alterations that take place during the combination of BSA and resistance exercise training. In addition, the following comparisons were of specific interest: 1) the comparative benefits of a short duration versus long BSA program and 2) a comparison of a short BSA program with the same short BSA program with the addition of resistance exercise.

METHODS

Experimental Approach

To address the primary hypotheses presented in this investigation, we needed to have a reduced-time BSA group with the addition of a resistance training program and compare this to the adaptations in a group using the same duration BSA program only and an additional group using a longer, more typical time frame for BSA. Thus, we could then determine whether resistance training caused any enhanced training adaptations beyond BSA alone. In addition, we could also determine the cost/benefit of using a reduction in duration to allow for the inclusion of a resistance training program and whether it reduced the adaptations compared with a longer-duration BSA program. Endurance training consisted of two BSA programs (25 and 40 min in duration) and a 25-min BSA program performed along with a strength/endurance training program three times per week for 12 wk. Participants were tested before and after the 12-wk training period to determine differences in body composition, muscular size, muscular strength, power, endurance, and aerobic capacity. All participants were completely familiarized with all testing and training protocols before the start of the study. This study represented a highly supervised training study. All participants were monitored by members of the research team during each training session. A certified exercise instructor lead all training sessions, and other members of the research team monitored each participant during training sessions. Each participant recorded all of her exercise data, which were also carefully monitored by the members of the research team (e.g., heart rate, step height, and levels of resistance). In this study, adherence to the program was 100%, with all participants completing 36 injury-free workouts over the 12-wk training program.

Subjects and Experimental Groups

Each participant was randomly placed into one of the groups (12 women targeted for each exercise group and 6 for the control group). Over the course of the investigation, seven women could not complete the study for reasons not related to the study protocol (e.g., job change, work schedule change, and move from town). By the end of the study, 35 healthy, active women had completed the study. Statistical analysis demonstrated that participants were not different in their body mass, age, and O2 peak before the study despite the loss of seven women. Each woman was randomly placed into one of four groups: group 1 performed 25 min of step-aerobics only (SA25) N = 8; group 2 performed 25 min of step-aerobics and a multiple-set upper and lower body resistance exercise program (SAR) N = 9; group 3 performed 40 min of step-aerobics only (SA40) N = 12; and group 4 acted as a control group (C) N = 6, whose members only continued to perform normal daily activities. It has been shown that at least 20 min of BSA are needed to enhance aerobic fitness, whereas at least 30–40 min are needed to yield a kcal expenditure conducive to weight loss (29). Thus, 25 and 40 min were chosen as the training durations for the BSA in this study. Subject characteristics are summarized in Table 1.

Table 1
Table 1:
Characteristics of the experimental subjects (mean ± SD).

Each woman gave written informed consent to participate in the study after all of the experimental risks, procedures, physical challenges, and time demands were explained. The protocol was approved by the Institutional Review Board for use of Human Subjects at the university, and the study was conducted in accordance with the guidelines for use of human subjects as stipulated by the American College of Sports Medicine. All women were medically screened before participation to assure that no prior medical problems contraindicated their ability to perform the programs (i.e., orthopaedic problems or pathological disease states). In addition, all participants were screened by our registered dieticians and counseled so that adequate food composition and intake (as determined by a 3-d dietary record) was maintained during the study.

Training Programs

Step-aerobics training sessions.

Each BSA session was preceded by a 5–10 min warm-up period and concluded with a 5–10 min cool-down (in which both included stretching). The intensity of the workouts was gradually increased at a similar rate for all groups as participants improved their skill and fitness levels. All exercise was individualized. This was accomplished by increasing the rate and height of stepping, adding more vigorous arm movements, and utilizing various jumps in the workouts to maintain target heart rate. Participants were instructed on how to obtain a carotid heart rate during a prestudy familiarization session by our research team. Briefly, a Polar heart rate monitor was used in conjunction with these tutorial sessions. Each participant was instructed to obtain the carotid heart rate both at rest and during moderate exercise. At this time, one of our exercise specialists determined the heart rate via a Polar heart rate monitor and compared it to the value obtained by the participant. This process was repeated until each subject was able to accurately and consistently detect heart rate within 2–4 bpm during exercise. Therefore, all participants were able to accurately palpate carotid heart rate before initiating the study. Heart rates were obtained before warm-up, during the exercise training sessions, and during the cool-down to monitor intensity. All exercise groups maintained an exercise intensity of 80–90% of their individual maximal heart rate. In addition, members of the research team made periodic checks on the ability of each subject to obtain an accurate heart rate (i.e., use of heart rate monitor checks).

Heavy resistance exercise program.

The SAR group performed lower body heavy resistance exercises before the BSA, and the upper body heavy resistance exercises afterward (Table 2). This was done so that the intensity of the larger lower body strength exercises would not be compromised by prior fatigue (7). All exercises were performed in a full range of motion using various graduated width/thicknesses of elastic bands that could produce resistances from 1 kg to > 250 kg for an exercise if needed (Flexband, Jumpstretch, Inc., Boardman, OH). Thus, actual heavy resistance loading for major muscle groups could be accomplished with this unique rubber band equipment for all subjects in a class atmosphere. The bands provided an obvious ascending linear resistance pattern with the resistance increasing as the band was stretched for an exercise. Greater resistance was provided by either using larger bands or by adding a smaller band to add the necessary amount of resistance to maintain the targeted number of repetitions (repetition maximum [RM] zone of ± 1 rep). The selected resistance was used for completion of a 9- to 11-RM zone with a 10-repetition target. Initially, a 1- to 2-min rest period was used between sets and exercises, with longer rest periods used in the beginning of the workout when larger muscle group exercises were being performed with heavier absolute resistances (7).

Table 2
Table 2:
The resistance exercise protocol used in this investigation.

Experimental tests

Subjects were tested 1 wk before and after 12 wk of training. Experimental tests included body composition, aerobic fitness, muscle morphology, and strength and power abilities. A careful familiarization phase was undertaken with each participant before the start of the study so that learning effects would be minimized. Pursuant to this end, all tests demonstrated interclass correlation coefficients of R > 0.94 for test–retest reliabilities. All measurements for testing (pretraining and posttraining) were made with the identical equipment, positioning, test technicians, and technique for each subject.

Peak aerobic power.

The aerobic power assessment was performed via a graded ˙VO2 peak test on a Monarck cycle ergometer (Recreation Equipment Unlimited, Inc., Pittsburgh, PA) with methods previously described (23). Briefly, the test began with an exercise intensity of 50 W with a pace of 60 rpm kept via an audible metronome cue. The resistance was increased by 50 W every 2 min during the test. Oxygen consumption and carbon dioxide production was monitored via an on-line breath-by-breath computerized indirect spirometry system with oxygen and carbon dioxide analyzers (Applied Electochemistry S3A and CD3A, Ametek Thermax Instrument Division, Pittsburgh, PA). Analyzers were calibrated before each test with known calibration gases. A rigorous evaluation of peak oxygen consumption was made as oxygen consumption was averaged over 15 and 30 s, and peak oxygen consumption was determined as the highest minute value during the test. Heart rate was determined via a Marquette (Milwaukee, WI) electrocardiograph every minute of the test, and ratings of perceived exertion (Borg Scale, 6–20 scale) were also obtained. Blood pressure was obtained via standard methods before and immediately after the graded exercise test. The criteria used to terminate the graded exercise test was volitional fatigue after either a plateau in oxygen consumption or a RER < 1.1 was attained.

Body composition.

Hydrodensitometry was used to assess body density, from which fat-free mass and percent body fat were estimated using methods previously described in detail (23). Percent body fat was estimated using the equation of Siri (31). A secondary check of body fat was performed to monitor changes during the study using seven-site skin-fold measurements obtained with a Lange skin-fold caliper (Country Technology, Gays Mills, WI) according to the methods described by Jackson et al. (15). All tests were performed by the same investigators.

Muscle cross-sectional area analyses.

Thigh bone-free muscle cross-sectional area (CSA) of the dominant leg was assessed before and after the resistance training program using a MRI 0.5-Tesla super conduction magnet (Picker International Inc., Highland Heights, OH) with MR6B software. Images were obtained by alteration of the spin-lattice or longitudinal relaxation time (T1). T1 weighted images were obtained using repeat time (TR): 500 ms; echo time (TE): 13 ms; radio frequency (RF, at 90 degrees); and power absorption of 0.028 W·kg-1. Analysis of the muscle CSA was determined from the MRI scans using a gradient echo technique, which allows the greatest delineation and distinction between muscles. Once the participant was positioned within the magnet, the thigh of the dominant leg was supported under the knee to ensure that it was parallel to the MRI table, and the feet were strapped together to prevent rotation. A sagittal image of the thigh was obtained. A 15-slice grid was placed over the sagittal image, and transaxial images were obtained. Fifteen transaxial images of 1-cm thickness were obtained equidistantly between the base of the femoral head and mid-knee joint of the thigh. All MRI images were then ported to a Macintosh computer for calculation of total and individual muscle CSAs using a modified National Institute of Health (NIH) image software package. For the muscle CSA, slice eight was used (slice one being the base of the femoral head). Tissue CSA was obtained by using the NIH 1.55.20A Image Analysis pixel counting program. The same investigator made all area measurements, and the test–retest reliability intraclass correlation coefficient for this measurement was R = 0.99 (18).

The morphological changes in skeletal muscle were determined before and after training using a MRI 0.5-Tesla super conduction magnet (Picker International Inc.) with MR6B software. Images were obtained by alteration of the spin-lattice or T1. T1 weighted images were obtained using TR: 500 ms; TE: 13 ms; RF (at 90 degrees), and power absorption of 0.028 W·kg-1. Analysis of the muscle CSA was determined from the MRI scans using a gradient echo technique, which allows the greatest delineation and distinction between muscles. Once the participant was positioned within the magnet, the thigh of the dominant leg was supported under the knee to ensure that it was parallel to the MRI table, and the feet were strapped together to prevent rotation. A sagittal image of the thigh was obtained. A twelve slice grid was placed over the sagittal image and transaxial images were obtained. Fifteen transaxial images of 1-cm thickness were obtained equidistantly between the base of the femoral head and mid-knee joint of the thigh. All MRI images were then ported via an Microtek Scanner III scanner to a MacIntosh Quadra 800 computer for calculation of total and individual muscle CSAs using a modified NIH image software package. For muscle CSA, slice 8 was used (slice 1 being the base of the femoral head). Tissue CSA was obtained by using the NIH 1.55.20A Image Analysis pixel counting program. The mid-thigh section of C-5 was utilized for measurement of individual whole muscle and body fat CSA. A known distance of 15-cm vertical and horizontal on each scanned film was used to set the scale of 12.467 pixels·cm-1 (15 cm = 187 pixels) on the computer screen. CSA (cm2) was determined by tracing along the border of each muscle, and the inner and outer areas of fat in the midthigh region. Two hundred initial tracings with the dominant hand were used to establish tracing validity according to Blomstrand (1). The same investigator did all of the measurements with a reliability of R = 0.99. Interinvestigator validity for absolute magnitude of size measures were evaluated, and a R = 0.98 was observed. Thus, the time to time and magnitude of each measure was considered within the scope and followed established methods (1). The muscles measured included the vastus medialis (vsmd), vastus lateralis (vslt), vastus intermedius (vsit), and rectus femoris (rcfm) of the quadriceps; the biceps femoris, short (bfs) and long (bfl) heads, semitendinosus (st), and semimembranosus (sm) of the hamstrings; the gracilis (gra), sartorius (sar), and adductor group (adgr). The order of muscle CSA measurement was the rectus femoris, vastus lateralis, vastus intermedius, vastus medialis, sartorius, biceps femoris short head, biceps femoris long head, semitendinosus, semimembranosus, gracilis, adductor group, inner area, and outer area (6).

Strength and power tests.

Strength and power tests were performed using the Plyometric Power System (PPS) interfaced with a computer (Norsearch Limited, Lismore, Australia) (14,25). Standardized protocols for 1-RM strength testing consisting of the 1-RM shoulder press and squat were performed according to methods previously described (21). Briefly, all 1 RMs were determined within 3–5 sets after warmup sets were completed. The squat exercise was performed from a knee angle of 90° flexion to a standing position with the bar held in the high back squat position. The shoulder press exercise consisted of lifting the bar upwards vertically from the shoulder position to complete elbow extension while the participant was seated.

Upper and lower body power output assessments during loaded conditions were also assessed using the PPS (25). Upper body power was determined using the ballistic shoulder press with 30% of 1 RM, and lower body power was determined using the squat jump with both 30 and 60% of 1 RM during two subsequent randomized testing sessions. The PPS has been described elsewhere (14,25). Briefly, linear bearings attached to either end of the bar allowed it to slide up and down two steel shafts with minimal friction. Bar movement caused a sprocket to rotate an encoder (Omron) resulting in a 5 V (TTL) pulse for each 0.001 m of bar movement. These pulses along with a TTL signal indicating movement direction were fed into a CTM05 counter timer board (Computer Boards, Mansfield, MA). The system was calibrated before all testing by counting the total number of pulses produced as the bar is moved through its full vertical range of 2.8 m. One-way sprag clutches ensured that only the sprockets and encoder rotated during upward bar movement. An electromagnetic brake attached to this shaft allowed the bar to be stopped at the top of its movement range, thus allowing complete release from the subject for optimal power measurement. The PPS was interfaced to a computer for accurate measurement of force, acceleration, distance, and ultimately power. Three trials were performed for each exercise with the highest score used for analysis.

Vertical jump power performance.

Maximal power output (via an unloaded condition) was determined by performance of counter movement vertical jumps (hands on hips) on an AMTI (Advanced Medical Technology, Inc., Newton, MA) force plate system interfaced with a computer. Customized software was used to calculate maximal power and force output. Subjects performed three single maximal-effort counter movement vertical jumps with 2 min of rest between trials, and the highest score was recorded for analysis.

Statistical Analyses

Standard statistical methods were used to calculate means and standard deviations. MANOVA with repeated measures was used to analyze pretraining and posttraining data. Subsequent Tukey post hoc tests were utilized to determine pairwise differences when appropriate. When statistical significance was reached for a specific variable from pretraining to posttraining, an independent t-test (alpha correction for 0.05 when needed) was used to analyze the delta change between training groups. Using the nQuery Advisor® software (Statistical Solutions, Saugus, MA) the statistical power for the N size used ranged from 0.80 to 0.92. Statistical significance was chosen as P = 0.05 for this investigation.

RESULTS

Changes in cardiovascular fitness are presented in Table 3. All training groups significantly improved peak ˙VO2 posttraining (P < 0.05). Heart rates obtained immediately before the workout protocol decreased significantly in all three training groups over the 12-wk training period. Likewise, heart rates obtained immediately after the workout protocol decreased significantly in the SA25 and SAR groups. No significant differences were observed for resting systolic blood pressure in any group. However, significant reductions in resting diastolic blood pressure were observed for the SAR and SA40 groups (P < 0.05). No differences were observed in the SA25 group. Systolic blood pressure in response to maximal cycle exercise decreased significantly in all three training groups, whereas only the SAR group showed a significant decrease in diastolic blood pressure during maximal cycle exercise. Ratings of perceived exertion (RPE) during maximal exercise decreased significantly in the SA25 and SAR groups, whereas no difference was observed in the SA40 group. No differences were observed in the C group for any variable.

Table 3
Table 3:
Changes in cardiovascular and metabolic function (mean ± SD).

Muscular performance data are presented in Table 4. The SAR group increased 1-RM squat and shoulder press significantly (26 and 17%, respectively). The SA25 and SA40 groups only showed insignificant improvements in 1-RM squat (9 and 16%, respectively) and shoulder press (5% for both groups). Only the SAR group significantly improved cycle time to exhaustion (P < 0.05). All training groups showed similar significant increases in jump squat power with both 30 and 60% of 1 RM. However, only the SAR group showed a significant increase in shoulder power with 30% of 1 RM. Only the SAR group showed a significant increase in peak vertical jump power. The C group did not show any significant changes in muscular performance.

Table 4
Table 4:
Changes in muscular performance and body composition (mean ± SD).

Body composition data are also presented in Table 4. No significant differences were observed in either body mass or fat-free mass in any group. However, a trend for an increase in fat-free mass was observed for the SAR and SA40 groups (P = 0.08 and 0.07, respectively). Percent body fat decreased significantly in all training groups. No differences were observed in the C group for any variable.

Changes in the quadriceps muscles as determined by MRI are shown in Figure 1. Muscle CSA for the rectus femoris and the vastus lateralis muscles increased significantly with training for only the SAR group (P < 0.05). In addition, no significant changes were observed in the vastus intermedius or vastus medialis muscles in any group. However, the SAR group did show a trend (P = 0.06 and P = 0.08, respectively) for increases in these two muscles. The SA25, SA40, and C groups did not show any changes in muscle CSA. Changes in hamstring muscles CSA are shown in Figure 2. The SAR group increased CSA of the short head of the biceps femoris and semitendinosus muscles. A significant increase in semitendinosus CSA was also observed in the SA40 group. Figure 3 panel C displays changes in CSA of other muscles of the thigh. The adductor group and gracilis muscles demonstrated an increase in CSA in the SAR group only. The sartorius muscle was not affected by any of the training programs.

Figure 1
Figure 1:
MRI of the quadriceps thigh musculature in the different training groups. *P < 0.05 from corresponding pretraining value.
Figure 2
Figure 2:
MRI of the hamstring thigh musculature in the different training groups. *P < 0.05 from corresponding pretraining value.
Figure 3
Figure 3:
MRI of the other thigh musculature in the different training groups. *P < 0.05 from corresponding pretraining value.

DISCUSSION

This investigation represents the first comprehensive study examining the training effects of BSA. Furthermore, we tried to extend the concept of how BSA may be used as a part of a total body conditioning program by adding a significant resistance training component within the exercise session. In addition, we were able to maintain a leader-class format with the use of graduated rubber bands capable of providing progressive heavy resistance training. The primary findings of this investigation were: 1) resistance training can augment improvements in aerobic fitness in combination with BSA; 2) the addition of a resistance training component contributes to the development of greater morphological changes in muscle and strength and power production not attained with BSA alone; and 3) BSA is capable of enhancing some basic strength and power characteristics of the lower body leg musculature. It appears that the use of the stretch-shortening cycle in the stepping, jumping, and bounding movements may mediate these performance gains beyond typical aerobic conditioning (7). We had theorized that the use of progressively greater resistance (i.e., larger exercise Flex-Bands), which more closely mimics the quality of resistance one can obtain via various free weights or machines in a formal weight room, contributed to the greater force production improvements observed in the SAR group. This is beyond what might be expected with the use of light hand weights typically used with BSA classes.

With acute exercise, BSA has been shown to significantly increase heart rate (i.e., ranging from 135 to 174 bpm), oxygen consumption (up to 37.3 mL O2·kg-1·min-1), and minute ventilation comparable to high- and low-impact aerobics (2), especially when faster stepping rates (32), larger bench steps (26), more complex movements (29), and hand-held weights were incorporated into the program (26,29). Stanforth et al. (32) showed that 86% of the variance in metabolic demands of BSA could be accounted for by step height (66%), body weight (17%), stepping rate (1.6%), fat-free mass (1.4%), and total leg length (0.5%). Thus, improvements in aerobic capacity with training may not be surprising. The data from the current investigation demonstrated that all three training protocols significantly increased peak ˙VO2 posttraining (SA25, 12%; SA40, 14%; SAR, 18%), despite the reduction in training time to 25 min in two of the groups. Remarkably, the increase (18%) observed for the SAR group was significantly greater than the increase observed for the SA25 group (12%), indicating that a resistance training program enhances the peak aerobic capacity as we have previously demonstrated in women undergoing a weight-loss program (23). Nevertheless, these data showed that all groups benefited in aerobic fitness from the BSA program and are consistent with other studies (i.e., 11–16% increase in ˙VO2max) examining aerobic development during similar training durations (29).

Consistent with the finding of enhanced peak ˙VO2 in the SAR group over BSA alone, we also observed increased cycle time to exhaustion. This finding supports our prior data in women undergoing weight loss (23) and is consistent with previous data in men, which have also demonstrated this adaptation when both resistance and endurance training are performed in a fitness program (12,13). The resistance training program used in this study included a high local muscular endurance component in its design consisting of multiple sets, relatively short rest periods (1–2 min), and loads allowing 10 repetitions (20). In addition, the program was performed within the context of an intense BSA program. The adaptations of improved force production (i.e., strength and power) and enhanced muscle tissue mass may mediate this performance gain. One may speculate that the ability to produce force above the “anaerobic threshold” was also enhanced (19). Neither BSA training group showed significant differences pretraining to posttraining, underscoring the importance of the resistance training program to this adaptation.

The cardiovascular responses of heart rate and blood pressure demonstrated that the addition of resistance training had a distinct influence on these adaptations. The results of our study showed that all exercise groups significantly decreased preexercise heart rate and both the SA25 and SAR groups decreased postexercise heart rates after 12 wk of training. A significant reduction in postexercise heart rates was observed in the SA25 and SAR groups. Typically, no changes or small decreases (2–5 bpm) in maximal heart rate after training have been reported in the literature (24). Thus, the decreases observed in the present study were not surprising. However, the magnitude of decrease was surprising based on the previous literature. One may question the effort put forth by the participants in the present study as submaximal during the graded exercise test. However, this was not the case. Of the criteria used for determination of maximal effort during ˙VO2 peak testing, RER values have been used. Recently, Duncan et al. (5) have shown that secondary to obtaining a plateau in oxygen consumption during maximal testing, RER and lactate values increase the likelihood that the highest ˙VO2 has been attained. In their study, only 10 and 40% of the subjects attained maximal predicted heart rate during discontinuous and continuous ˙VO2 testing, respectively. However, the RER and lactate criteria were reached in 90–100% of the subjects, indicating that heart rate may not be the best criterion. These authors concluded that the variability in maximal heart rate was too large to use as the sole criterion for ˙VO2 testing. In the present study, RER values were well beyond the accepted criteria of 1.15 (range, 1.27 to 1.45). Thus, our data indicate that peak ˙VO2 was attained and either are consistent with the study by Duncan et al. (5) indicating a high variability of heart rate during maximal testing or reflect a potential beneficial cardiovascular adaptation to BSA exercise.

Different from what might be expected from aerobic training (3), no significant changes in resting systolic blood pressure were observed in the present study indicating variable adaptations in normotensive women. However, the systolic blood pressure responses to maximal exercise were decreased in all training groups. Interestingly, both high-volume exercise groups (i.e., SAR and SA40) demonstrated decreased resting diastolic pressure (5–6 mm Hg), whereas the low-volume group (SA25) did not. These data are consistent with Kelley and Tran (16), who used a meta-analysis and reported a mean reduction of 3–4 mm Hg in diastolic blood pressure after an exercise program. From these data, it appears that the total volume of exercise may be an important factor in this specific cardiovascular adaptation. The addition of resistance training to 25 min of BSA provided a sufficient volume of exercise to enhance resting diastolic blood pressure. In addition, only the SAR group demonstrated a significant decrease in the diastolic blood pressure response to maximal exercise. This may be due to alterations in the pressor effects to the higher loads in the cycle test. Although resistance training is not typically thought to affect many cardiovascular adaptations, this investigation demonstrates that its influence is greater than previously demonstrated.

As might be expected, based on specificity of training, the results of the muscular strength assessments demonstrated that only the SAR group increased both squat and shoulder press 1-RM strength (7). The SAR group increased 1-RM squat and shoulder press by 27 and 17%, respectively, whereas the SA25 and SA40 groups increased squat 1 RM by 9% and 16%, respectively, and shoulder press 1 RM by 5% for both groups. These data do show that an aggressive BSA program will influence the maximal force production in the lower body, but not to the extent of a heavy resistance training program. However, a distinct lack of change in the upper body was evident even with rigorous arm use of the upper body movements with the BSA program. In a prior investigation, Koenig et al. (17) reported a significant decrease in quadriceps strength (i.e., knee extensions) and no change in hamstring strength (i.e., leg curls) following 10 wk of BSA. Differences in the two investigations may be partially explained by different exercise testing movements used in the study of Koenig et al. (17). In contrast, we used a squat exercise test, which as a closed kinetic chain exercise better reflects the movements used in BSA. The increases in the 1-RM squat strength represent a total-body structural strength increase that has ramifications for everyday functional abilities, bone health, and physical performance. The shoulder press was used as a marker of upper body strength changes. The BSA program consisted of only unloaded shoulder and upper body movements, which were obviously not adequate for improving upper body strength. Therefore, the addition of resistance exercises for the upper body resulted in significant increases in upper body strength in the SAR group beyond that observed from using unloaded upper body movements during the BSA program. With the importance of upper body training in women, our total body conditioning program was successful at improving this important element in strength fitness in women (23).

Based on the results of the present study, it does not appear that simultaneous training negatively impacts the fitness adaptations when adequate recovery between workouts is allowed. Inclusion of both resistance exercise and BSA did not limit any cardiovascular or muscular performance adaptations. This was the first study to show that in healthy women, higher-intensity simultaneous exercise training performed three times per week does not promote any type of exercise incompatibility or overtraining. We felt that this was the case in a prior study but did not have any direct experimental evidence to support this hypothesis (23). Using much lower intensities of exercise for strength and endurance training, Volpe et al. (35) previously found that endurance running did not interfere with lower body strength improvements achieved through weight training, nor did the strength training interfere with aerobic improvements. Previous investigations in men have shown a potential for incompatibility between mutual high-intensity strength and endurance training with the primary reason being attributed to potential acute overtraining phenomenon (11,22,28).

The results of this investigation demonstrated that all of the training groups significantly improved power output during both loaded conditions (30 and 60% of 1 RM). In the progression of the BSA program, additional power-type movements (e.g., jumps, deep knee bend jumps, and greater step height) were included. These data demonstrate that BSA alone can enhance power development in the lower body. Several factors may influence the power development observed with BSA. Previous investigations have shown vertical impact forces ranging from 1.4 to 1.87 times body weight during BSA (30). Vertical impact forces may increase if complex movements are performed, greater step rates are used, and if higher steps are used (29). Thus, these data demonstrate that a substantial impact force component is placed on the lower body musculature in a plyometric manner over longer durations. The aggressive stretch-shortening cycle nature of the BSA modality demonstrates an effective means for increasing muscular power (during loaded conditions) in women. Interestingly, only the SAR group demonstrated a significant increase in peak power during the unloaded vertical jump test. The BSA programs used in this study produced significant increases in power using the lightly (30%) and moderately (60%) loaded jumps tests. These data demonstrated that the BSA programs were more sensitive to the loaded conditions. It is quite possible that the BSA programs provided more loading than the typical vertical jump test due to mechanical forces in the dynamic stretch-shortening cycle (10). The addition of resistance training in the SAR group appears to have increased strength and power at the base of the vertical jump to augment the power equation component of force at the bottom of the jumping movement (25). This type of stretch-shortening cycle activity (i.e., plyometric training) has been shown to improve muscular power capabilities (9). With the importance of high-impulse activities to bone health in women, BSA combined with a resistance training program appears to offer an optimal combination of exercise stimuli.

Few data are available examining the effects of training on upper body power in women. In this investigation, upper body power significantly increased only in the SAR group. Concomitant with the improvements in 1-RM strength, this adaptation in the SAR group can be explained by specific training of the involved upper body musculature. No externally loaded movements were used for the upper body in the SA25 and SA40 groups. BSA movements were performed rapidly, but these data indicate that loading of the joint segment is vital for increasing muscular power. The addition of resistance training in the SAR group provided the external loading needed to make initial improvements in muscular power. Therefore, it appears that resistance training is warranted to increase upper body power in women and can be accomplished within the context of a classically targeted aerobic exercise program such as BSA.

Unique to this study was the examination of the lower body musculature morphological changes with BSA and resistance training using MRI technology. Our finding that the SAR group significantly increased the CSA of various muscles of the thigh represents a unique glimpse into the training effects of BSA and the actual influence of heavy resistance training using alternative equipment. From the experimental design perspective, it appears that the resistance training program contributed the primary stimulus for hypertrophy because few increases in CSA adaptations in whole muscle morphology were observed in the BSA programs. Yet some changes were observed, indicating that stretch-shortening cycle overload of the musculature may affect certain muscles more than others over a short-term training program of 3 months. Potteiger et al. (27) have previously shown in men that muscle fiber hypertrophy is possible in the vastus lateralis muscle with stretch-shortening cycle (i.e., plyometrics) training alone. Such data support our findings of hypertrophy in various muscles of the SA25 and SA40 BSA groups. The impact of longer-term training on muscle morphology with this plyometric-style training remains to be further examined. The efficacy of graduated rubber band resistances capable of implementing progressively greater resistance within a class format makes such a program possible without formal weight training equipment. Classical resistance exercise modalities (barbell and plate stack machines) have been shown to significantly increase muscle CSA in women, especially Type I fibers at the cellular level (10,33,34). Nevertheless, it appears that the great vertical impact forces produced during BSA alone do very little to stimulate dramatic hypertrophy in the thigh musculature. The lower magnitude of gains in strength and power following BSA alone may be mediated by neurological and quality of protein (e.g., shifts in myosin ATPase and myosin heavy chain proteins to faster types) adaptations that have been shown to take place during the first 2 wk of training (33,34).

Changes in body composition have been an important training feature in many physical fitness programs for women (7). Percent body fat decreased significantly in all of the training groups despite no direct control of nutritional intakes (i.e., diets remained constant throughout the study with no reductions in caloric intake). Decreases in the percent body fat are typical of both endurance and resistance training programs (33,34) and especially with a weight loss program in women (23). No differential effects of the training modality were apparent because the magnitude of decrease was not different between the groups. Therefore, these data indicate that the aerobic component of the exercise training program may be the most important element of program design to impact body fat stores over short-term training periods (22). Mechanisms related to resistance training may take a longer period of time to impact body fat stores without modulation of caloric intake (23).

There is a distinct need to optimize physical conditioning programs for women’s health. This investigation pointed to the importance of a resistance component in a typical aerobic conditioning program used by many women in gyms, health clubs, and fitness facilities. This investigation provided provocative evidence that the entire physical fitness can be enhanced with just the addition of a heavy resistance training program. Unique to this investigation, it was shown that this can be done within a class format of a BSA program with the use of alternate forms of resistance training equipment. Differential effects were observed among the three different programs, indicating training specificity for strength and power, body composition, and cardiovascular adjustments. The addition of resistance exercise to BSA appears to offer advantages for improving muscular performances greater than that of performing only BSA. This investigation confirmed the beneficial nature of this type of exercise training in women. Considering the importance of physical fitness and women’s health, this investigation demonstrates important new findings utilizing both BSA and resistance exercise training.

This research was supported in part by a grant from Nike Inc., One Bowerman Drive Beaverton, OR 97005-6453 to W.J.K. We would also like to thank Dr. Gordon Valiant of Nike for his support of this research program. In addition, the authors acknowledge Dick Hartzell, JumpStretch, Inc., for donating the FlexBands that gave us a unique resistance exercise equipment for this training program. We would like to give a special thanks to all of the subjects in this study—without their dedication and hard work, this study would not have been possible. We would like to thank Linda Silveri and David B. Corneal of the Athletic Clubs, State College, PA for their support of the project and Ms. Silveri for her hard work in developing the BSA program and heading up a super group of BSA exercise leaders; also to April Polito for her work in the testing and exercise leadership in the project. We thank Mr. and Mrs. John Fisher for their support of the HPL at Ball State University. Finally, we would like to thank all of the medical and research staffs who helped to make the many dimensions of this project work.

Address for correspondence: William J. Kraemer, Ph.D., FACSM, Director/Professor, The Human Performance Laboratory, Ball State University, Muncie, IN 47306. E-mail: wkraemer@bsu.edu.

REFERENCES

1. Blomstrand, E., F. Celsing, J. Friden, and B. Ekblom. How to calculate human muscle fibre areas in biopsy samples-methodological considerations. Acta Physiol. Scand. 122: 545–551, 1984.
2. Clapp, J. F., and K. D. Little. The physiological responses of instructors and participants to three aerobics regimens. Med. Sci. Sports Exerc. 26: 1041–1046, 1994.
3. Clausen, J. P. Effect of physical training on cardiovascular adjustments to exercise in man. Physiol. Rev. 57: 779–816, 1977.
4. Dudley, G. A., and R. Djamil. Incompatibility of endurance and strength training modes of exercise. J. Appl. Physiol. 59: 1446–1451, 1985.
5. Duncan, G. E., E. T. Howley, and B. N. Johnson. Applicability of VO2 max criteria: discontinuous versus continuous protocols. Med. Sci. Sports Exerc. 29: 273–278, 1997.
6. Engstrom, C. M., G. E. Loeb, J. G. Reid, W. J. Forrest, and L. Avruch. Morphometry of the human thigh muscles: a comparison between anatomical sections and computer tomographical and magnetic resonance images. J. Anat. 176: 139–156, 1991.
7. Fleck, S. J., and W. J. Kraemer. In: Designing Resistance Training Programs, 2nd Ed. Champaign, IL: Human Kinetics Publishers, 1997, pp. 183–197.
8. Francis, L. L. Step aerobics. ACSM Certified News. 2: 1–4, 1992.
9. Häkkinen, K., and A. Pakarinen. Serum hormones in male strength athletes during intensive short term strength training. Eur. J. Appl. Physiol. 63: 194–199, 1991.
10. Häkkinen, K., A. Pakarinen, and M. Kallinen. Neuromuscular adaptations and serum hormones in women during short-term intensive strength training. Eur. J. Appl. Physiol. 64: 106–111, 1992.
11. Hickson, R. C. Interference of strength development by simultaneously training for strength and endurance. Eur. J. Appl. Physiol. Occup. Physiol. 45: 255–269, 1980.
12. Hickson, R. C., M. A. Rosenkoetter,and M. M. Brown. Strength training effects on aerobic power and short-term endurance. Med. Sci. Sports Exerc. 12: 336–339, 1980.
13. Hickson, R. C., B. A. Dvorak, E. M. Gorostiaga, T. T. Kurowski, and C. Foster. Potential for strength and endurance training to amplify endurance performance. J. Appl. Physiol. 65: 2285–2290, 1988.
14. Humphries, B. J., R. U. Newton, and G. J. Wilson. The effect of a braking device in reducing the ground impact forces inherent in plyometric training. Int. J. Sports Med. 16: 129–133, 1995.
15. Jackson, A. S., M. L. Pollock, and A. Ward. Generalized equations for predicting body density in women. Med. Sci. Sports Exerc. 12: 175–182, 1980.
16. Kelley, G., and Z. V. Tran. Aerobic exercise and normotensive adults: a meta-analysis. Med. Sci. Sports Exerc. 27: 1371–1377, 1995.
17. Koenig, J. M., D. M. Jahn, T. E. Dohmeier, and J. W. Cleland. The effect of bench step aerobics on muscular strength, power, and endurance. J. Strength Cond. Res. 9: 43–46, 1995.
18. Kraemer, W. J., B. J. Noble, B. Culver, and R. V. Lewis. Changes in plasma proenkephalin peptide F and catecholamine levels during graded exercise in men. Proc. Natl. Acad. Sci. 82: 6349–6351, 1985.
19. Kraemer, W. J., B. J. Noble, B. W. Culver, and M. J. Clark. Physiologic responses to heavy-resistance exercise with very short rest periods. Int. J. Sports Med. 8: 247–252, 1987.
20. Kraemer, W. J., and L. P. Koziris. Muscle strength training: techniques and considerations. Phys. Ther. Pract. 2: 54–68, 1992.
23. Kraemer W. J., and A. C. Fry. Strength testing: development and evaluation of methodology. In:Physiological Assessment of Human Fitness, P. Maud and C. Foster (Eds.). Champaign, IL: Human Kinetics, 1995, pp. 115–138.
22. Kraemer, W. J., J. F. Patton, S. E. Gordon, et al. Compatibility of high-intensity strength and endurance training on hormonal and skeletal muscle adaptations. J. Appl. Physiol. 78: 976–989, 1995.
21. Kraemer, W. J., J. S. Volek, K. L. Clark, et al. Physiological adaptations to a weight-loss dietary regimen and exercise programs in women. J. Appl. Physiol. 83: 270–279, 1997
24. Lieber, D. C., R. L. Lieber, and W. C. Adams. Effects of run-training and swim-training at similar absolute intensities on treadmill VO2 max. Med. Sci. Sports Exerc. 21: 655–661, 1989.
25. Newton, R. U., W. J. Kraemer, and K. Häkkinen. Effects of ballistic training on preseason preparation of elite volleyball players. Med. Sci. Sports Exerc. 31: 323–330, 1999.
26. Olson, M. S., H. N. Williford, D. L. Blessing, and R. Greathouse. The cardiovascular and metabolic effects of bench stepping in females. Med. Sci. Sports Exerc. 23: 1311–1318, 1991.
27. Potteiger, J. A., R. H. Lockwood, M. D. Haub, et al. Muscle power and fiber characteristics following 8 weeks of plyometric training. J. Strength Cond. Res. 13: 275–279, 1999.
28. Sale, D. G., J. D. Macdougall, I. Jacobs, and S. Garner. Interaction between concurrent strength and endurance training. J. Appl. Physiol. 68: 260–270, 1990a.
29. Scharff-Olson, M., H. N. Williford, D. L. Blessing, and J. A. Brown. The physiological effects of bench/step exercise. Sports Med. 21: 164–175, 1996.
30. Scharff-Olson, M., H. N. Williford, D. L. Blessing, R. Moses, and T. Wang. Vertical impact forces during bench-step aerobics: exercise rate and experience. Percept. Mot. Skills 84: 267–274, 1997.
31. Siri, W. E. Body composition from fluid spaces and density: analysis of methods. In:Techniques for Measuring Body Composition, J. Brozek and A. Henschel (Eds.). Washington, D.C.: National Academy of Science, 1961, pp. 223–244.
32. Stanforth, D., P. R. Stanforth, and K. S. Velasquez. Aerobic requirement of bench stepping. Int. J. Sports Med. 14: 129–133, 1993.
33. Staron, R. S., M. J. Leonardi, D. L. Karapondo, et al. Strength and skeletal muscle adaptations in heavy-resistance-trained women after detraining and retraining. J. Appl. Physiol. 70: 631–640, 1991.
34. Staron, R. S., D. L. Karapondo, W. J. Kraemer, et al. Skeletal muscle adaptations during the early phase of heavy-resistance training in men and women. J. Appl. Physiol. 76: 1247–1255, 1994.
35. Volpe, S. L., J. Walberg-Rankin, K. W. Rodman, and D. R. Sebolt. The effect of endurance running on training adaptations in women participating in a weight lifting program. J. Strength Cond. Res. 7: 101–107, 1993.
Keywords:

STRENGTH TRAINING,; PHYSICAL FITNESS,; POWER,; MUSCLE MORPHOLOGY

© 2001 Lippincott Williams & Wilkins, Inc.