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Original Research

Physiologic and Metabolic Responses to a Continuous Functional Resistance Exercise Workout

Lagally, Kristen M; Cordero, Jeanine; Good, Jon; Brown, Dale D; McCaw, Steven T

Author Information
Journal of Strength and Conditioning Research: March 2009 - Volume 23 - Issue 2 - p 373-379
doi: 10.1519/JSC.0b013e31818eb1c9
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Abstract

Introduction

The term “functional training” describes multiplanar, multijoint resistance exercises that simulate movement patterns from everyday life and sport. Functional training is believed to enhance neuromuscular coordination, with the assumption that the neuromuscular improvements will enhance performance in activities of daily living (ADLs) or sport (4). However, although functional training has increased in popularity, the cardiovascular and muscular benefits have not been quantified. Most publications on functional training are primarily descriptive or provide anecdotal information (4,16). There is limited research documenting improvements in physiological response after training, and the only empirical evidence is on the effects of a functional exercise program on the performance of ADLs in older adults (6,18).

De Vreede et al. (6) have compared the effects of functional exercises vs. resistance exercises on daily living task performance in elderly women. The daily living tasks included movements with vertical and horizontal components, carrying an object, and changing between lying, sitting, and standing postures. The subjects in the resistance exercise group performed 30 minutes of resistance exercise training in the muscle groups deemed important for daily task performance. The exercises were performed in sets of 10 repetitions. The subjects in the functional training group performed activities that mimicked the target daily living tasks in sets of 5-10 repetitions, with resistance increased on the basis of subject tolerance. A control group maintained typical daily activity. At the end of 12 weeks of participation, the functional training group exhibited the greatest improvements in task performance (as measured by the Assessment of Daily Activity Performance), although the resistance exercise group exhibited the greatest improvements in strength. The functional training group also maintained their task performance gains 6 months after the program. The authors attribute their results to the enhanced specificity of the functional training over the resistance exercise training in terms of cognitive, perceptual, and motor functions.

Functional resistance exercise training tends to emphasize neuromuscular coordination, technique, posture, and core musculature engagement over the amount of resistance lifted, making it well suited for use in a continuous format with short or no rest periods, similar to circuit weight training. Previous research suggests that although circuit weight training can improve muscle fitness, it does not provide an adequate cardiovascular training stimulus or lead to large improvements in cardiovascular fitness (2,9-12,14,19). Performing functional resistance exercises in a continuous format has the potential to provide a better cardiorespiratory stimulus than circuit weight training through the use of dynamic traveling patterns within both upper and lower extremities. This allows continuous use of the large muscle groups, which is a recommended component of cardiorespiratory endurance exercise prescription (1). In addition, functional resistance exercises performed with a resistance imposing an overload are likely to improve muscular strength and endurance. An exercise mode incorporating both aerobic and resistance exercise components is highly desirable because combining both types of training would reduce the exercise session time requirement for participants, which could improve adherence to an exercise program (7). Given the increased availability of functional training equipment in fitness clubs, many participants would be able to perform functional exercise individually or in a group exercise format. With a paucity of research documenting the effects of functional training, the purpose of this investigation was to examine the physiological and metabolic responses to a single continuous functional resistance exercise (CFE) workout. We hypothesized that performing functional exercise in this format would meet the recommendations set by the ACSM for energy expenditure and cardiorespiratory training.

Methods

Experimental Approach to the Problem

Twenty women and men participated in baseline maximal oxygen consumption and strength testing before participation in 3 familiarization sessions and 1 data collection session during which they performed a 40-minute CFE routine. During the data collection session, oxygen consumption, respiratory exchange ratio (RER), heart rate, rating of perceived exertion (RPE), and blood pressure were measured throughout the functional exercise, and lactic acid concentration was measured pre- and postexercise. Caloric expenditure was calculated using oxygen consumption and RER values obtained during the exercise.

Subjects

Ten women and 10 men, ages 19-27 years old, volunteered to participate in this study. Subjects were recruited from kinesiology classes at a midwestern university. All subjects provided informed consent and completed a physical activity questionnaire (PAR-Q), medical history form, and an activity history questionnaire. Subjects self-reported being moderately trained, recreational weight lifters, with no functional training experience. A recreational weight lifter was defined as having lifted weights 2-3 times per week and having done so for at least 6 months. In addition, subjects reported that they were not taking performance-enhancing drugs at the time of the experiment and had no musculoskeletal disorders that would prohibit exercise testing. Subjects were required to abstain from food for at least 3 hours before testing and abstain from strenuous activity on the day of testing. The protocol was approved by the institutional review board of the university.

Procedures

Session 1: Assessments

Each subject was measured for height, weight, and body composition. Body composition was measured via skinfold caliper analysis, using the methods of Jackson and Pollock (13). After anthropometric data were collected, subjects underwent a maximal oxygen uptake test (o2max test) on a Quinton medical treadmill using the Bruce ramp protocol (1). Subjects were encouraged to exercise as long as possible. Oxygen uptake, blood pressure, and heart rate were monitored continuously throughout the test using a MedGraphics VO2000 portable metabolic system (St. Paul, Minn), a portable sphygmomanometer, and a Polar heart watch, respectively. o2peak was recorded as the highest oxygen uptake value obtained. The metabolic equipment was calibrated before exercise using autocalibration following the manufacturer's recommendation. Subjects also performed a submaximal (5-repetition maximum [RM]) test using the functional training equipment to identify the maximum resistance at which 5 repetitions of a single arm press could be performed while in a staggered stance. The criteria were to maintain proper form, defined as maintaining a neutral back and neck with a tight core, with no evident leaning, and no facial signs of physiological strain.

Sessions 2-4: Familiarization Sessions

After 2 days of rest, each subject participated in 3 familiarization sessions during which they followed a 40-minute videotaped routine of functional exercises choreographed and performed by a National Academy of Sports Medicine-certified master trainer using a FreeMotion cable column. The cable column has a pulley system that adjusts vertically from 36 to 213 cm, and contains a weight stack ranging from 5.5 to 110 kg, increasing by 5.5-kg increments. The cable allows 244 cm of travel. Cable attachments include 1 short and 2 long handles and an ankle cuff.

The routine included a 7-minute warm-up, 3 × 9.5-minute exercise segments, and a 4.5-minute cool-down. The format of the CFE workout was similar to circuit weight training in that the exercises were performed in succession. The total exercise time, not including warm-up and cool-down, was approximately 28.5 minutes. Each of the 3 exercise segments was performed with the cable secured at a different height on the column: low (36 cm), mid (127 cm), and high (213 cm). The routine, detailed in Table 1, included activities using whole-body movements and dynamic traveling patterns that reflect sport and activities of daily living-like characteristics. The warm-up and cool-down included basic arm and leg patterns and were performed with the cable secured at midheight. Warm-up exercises included overhead circles with a side lunge pattern, side-to-side rotation with a lunge pattern, and stationary overhead lift, all using light resistances. Each exercise segment included whole-body exercises with press, pull, and fly patterns for the upper body, and dynamic traveling patterns for the lower body, including side-to-side lunges, steps, or hops. Both the upper body and lower body were engaged for most exercises. A few exercises were highly sport-specific. For example, at the low height, subjects performed a “speed skater” movement with the resistance attached to the ankle cuff, and a tennis forehand and backhand with a travel pattern using a short handle attached to the weight stack of the cable column. Of the 21 total exercises, there were only 3 exercises that required the resistance to be attached to the ankle cuff. These were all performed at the low height. The remaining 18 exercises required the resistance to be lifted by the upper-body musculature in conjunction with lower-body movements or stabilization. Three exercises included single-leg stabilization while performing a fly or pull with the upper body. All exercises were performed for 10 repetitions on both the right and left sides and were performed in a continuous manner. The resistance was changed by the tester between exercises. There were 7 exercises performed at each handle height, and each exercise took approximately 1.5 minutes to complete.

Table 1
Table 1:
Exercise protocol.

During all familiarization sessions, subjects were monitored by a certified exercise specialist or personal trainer for correct form and technique. If subjects deviated from correct form, the trainer provided verbal and visual cues to correct the problem. During the first familiarization session, resistances were selected based on the ability of the subject to maintain proper form and adequately perform the exercise. In subsequent sessions, subjects were required to maintain the same pace as the video instructor and were encouraged to cover as much space as possible with their movements. The resistance was altered as deemed necessary by the trainer, based on subject performance and the subject's subjective tolerance of the resistance for a given exercise. For instance, if subjects were obviously struggling to maintain proper form and/or were performing the exercises at a slower pace than the video instructor, resistance was decreased. If subjects were moving too quickly or the cables were too slack, resistance was increased. Subjects gained skill across the 3 familiarization sessions and were all highly skilled by the final session; thus, the subjects were able to perform all exercises at the proper pace and with the proper form. This allowed a final determination of the target resistance for the data collection session by the third familiarization session. The mean resistance lifted for men was 11.2 ± 0.8 kg, and for women it was 6.5 ± 0.8 kg. Subjects were given at least 2 days of rest between each familiarization session and between the final familiarization session and the data collection session.

Final Session: Data Collection Session

For data collection, subjects performed the videotaped exercise routine used in the familiarization sessions. The final resistance from familiarization session 3 was used in this session. Subjects were fitted with a Polar heart watch and a belt that held the analyzer for the MedGraphics VO2000 system. Subjects also wore a neoprene mask connected by the sampling tubes to the analyzer. Oxygen uptake was monitored continuously via telemetry using the MedGraphics VO2000 portable metabolic system, calibrated as detailed above. Caloric expenditure was calculated using o2 and RER averaged for each minute of exercise in each segment. Heart rate was measured via telemetry using the Polar heart system. Blood pressure was measured pre- and postexercise using a portable sphygmomanometer. Ratings of perceived exertion for the overall body were assessed at the end of each exercise segment using the OMNI Scale for Resistance Exercise (OMNI-RES) to assess the subjects' exercise tolerance (15). Blood lactic acid was measured preexercise and 4 minutes postexercise by means of a finger prick and was measured with an Accusport portable lactate analyzer. Blood samples were taken from different fingers for the 2 measurements. As in the familiarization sessions, a certified exercise specialist or personal trainer monitored form and technique and changed the resistance, cable height, and attachments when necessary.

Statistical Analyses

Only data from the 3 exercise segments of the data collection session, not the warm-up and cool-down, were analyzed. Descriptive statistics (mean and SD) for subject characteristics, physiological, and metabolic variables were calculated for men, women, and all subjects combined. Independent t-tests were performed to compare men and women for RER, absolute and relative o2, % o2 reserve (% O2R), absolute and relative heart rate, average resistance lifted, average % 5RM lifted, difference in pre and post lactate values, overall RPE, energy expenditure (total kilocalories, kilocalories per minute, and kilocalories per kilogram per minute), percent fat, and body weight. The alpha level was adjusted using the Bonferroni procedure (0.05/15 = 0.003) where appropriate. Pearson correlations were calculated to examine the relationship between absolute and relative resistance lifted, relative o2, relative o2R, and absolute and relative energy expenditure. All analyses were carried out using SPSS software version 14.0 (SPSS, Chicago, Ill), and an alpha level of p ≤ 0.05 was used to establish statistical significance.

Results

The subject characteristics are presented in Table 1. Independent t-tests showed that there were significant differences between men and women in height, body weight, and percent fat. As expected, men were significantly taller and heavier and had significantly lower percentages of fat than women. There were no significant differences between men and women in age, maximum heart rate (HRmax), or o2max.

The descriptive statistics for the 28.5-minute CFE segment are presented in Table 2. As a group, subjects performed the functional workout at a mean o2 of 27.8 ± 5.4 ml·kg−1·min−1 (51.1 ± 9.7% o2peak and 47.8 ± 10.2% o2R) and a mean heart rate of 156 ± 13.9 bpm (82.7 ± 6.0% HRmax). The mean RER was 0.91 ± 0.05. The mean energy expenditure was 289.2 ± 82.2 kcal (10.2 ± 2.9 kcal·min-1, or 0.14 ± 0.03 kcal·kg−1·min−1). The mean post lactate value was 4.5 ± 1.3 mmol·L−1, and the pre-post lactate difference was 2.5 ± 1.4 mmol·L−1. Lactate data were not available for 1 subject because of equipment limitations. The mean RPE was 5.9 ± 1.5, or “somewhat hard.”

Table 2
Table 2:
Subject characteristics (mean ±SD).

Independent t-tests indicated no significant differences between men and women for RER, absolute or relative o2, % o2R, absolute or relative heart rate, relative resistance lifted (% 5RM), lactate difference, overall RPE, or energy expenditure when expressed as kilocalories per kilogram per minute. As would be expected, men lifted significantly (p < 0.001) heavier resistance than women when expressed absolutely (kg), and men also exhibited greater energy expenditure than women when expressed as kilocalories (p < 0.002) or kilocalories per minute (p < 0.002).

Pearson correlation coefficients were calculated with men and women combined and are presented in Table 3. The Pearson correlations indicate a moderate positive relationship between % 5RM lifted and % o2peak (r = 0.49, p < 0.05) and % o2R (0.50, p < 0.05) and between % 5RM lifted and energy expenditure in kilocalories per kilogram per minute (r = 0.50, p < 0.05). As expected, a strong positive relationship was found between energy expenditure expressed in relative terms (kcal·kg−1·min−1) and energy expenditure expressed in absolute terms (kcal·min-1 or kcal) (r = 0.68, p < 0.01). In addition, energy expenditure (kcal·kg−1·min−1, kcal·min−1, kcal) was related to both % o2peak (r = 0.75, 0.73, and 0.73, respectively; p < 0.01) and % o2R (r = 0.78, 0.74, and 0.74, respectively; p < 0.01). The correlation between absolute energy expenditure (kcal·min−1 or kcal) and absolute weight lifted in kilograms was also significant (r = 0.74; p < 0.01). No other significant correlations were found between absolute and relative resistance lifted, relative oxygen uptake, or absolute and relative energy expenditure (Table 4).

Table 3
Table 3:
Mean values (±SD) for physiologic and metabolic variables.
Table 4
Table 4:
Intercorrelation matrix between weight lifted, energy expenditure, and relative oxygen uptake (N = 20).

Discussion

The purpose of this investigation was to examine the physiologic and metabolic responses to a CFE workout. The format of the workout included dynamic functional exercises that engaged both the upper and lower body simultaneously and incorporated dynamic traveling patterns. It was hypothesized that the functional exercise performed in a continuous manner would meet the recommendations of the American College of Sports Medicine (ACSM) for energy expenditure and for improving cardiovascular fitness.

According to the ACSM, the recommended guidelines for improving cardiovascular fitness are to perform exercise at an intensity of 50-85% o2R (1). The ACSM also recommends an energy expenditure of 150-400 kcal·d−1 from physical activity (1). The CFE workout examined in this investigation meets the energy expenditure recommendations, with a mean expenditure of 289 kcal for 28.5 minutes of exercise. However, as a group, subjects performing the CFE workout did not meet the ACSM intensity recommendations for improving cardiovascular fitness, because the mean % o2R was 47.8%. It is important to note that maximal oxygen uptake was measured in a mode different from the exercise mode performed in the data collection session. A mode-specific o2peak value may have produced different results in terms of the relative oxygen uptake achieved during the CFE workout.

The individual average % o2R from the CFE workout ranged from 33 to 68% across subjects. Fifty percent of subjects performed the workout at an oxygen uptake value that fell within the ACSM recommendations of 50-85% o2R. This variation in oxygen consumption was not explained by the variation in absolute resistance lifted, because the correlation (r = 0.27) was low and nonsignificant. Thus, those who lifted heavier resistances did not necessarily have greater relative oxygen consumption. The correlation improved somewhat (r = 0.50, p < 0.05) when the relative resistance lifted (% 5RM) was correlated with the % o2R value achieved during the CFE workout. Although it was difficult to get a meaningful assessment of maximal strength specific to the equipment used, these results suggest that the relative resistance lifted explained about 25% of the variation in the oxygen requirement of the activity. Increasing the resistance lifted has been advocated by some researchers and practitioners as a method of increasing the aerobic requirement of circuit weight training (5), although others speculate that increasing resistance is not a viable option (8,20). In the present study, the average RPE was a 6, or “somewhat hard,” on the OMNI-RES. Thus, we would caution against increasing the resistance much more because it could result in poor technique, increased injury, and decreased adherence, particularly in individuals who are new to functional resistance exercise training. Although speculative, other factors that may have contributed to the higher relative oxygen uptake values seen in half of the subjects are the amount of space covered with the movements and the extent of core musculature engagement. We noted anecdotally that subjects who used larger movements and exhibited high core engagement tended to have higher o2 values during the workout. Because our design was limited in this aspect, future investigations should examine the impact that these factors have on oxygen consumption during functional resistance exercise.

The relative and absolute oxygen uptake values from the present study are similar or slightly higher than those reported for circuit weight training (2,8,11,12,19), the closest comparable activity. No previous investigations have reported oxygen uptake values as % o2R, and the highest % o2max value found in the circuit weight training literature was 50% o2max (8). This value was only attained after the completion of 3 exercise circuits, so oxygen consumption earlier in the circuit weight training workout was even lower. By comparison, the relative oxygen uptake values in the present study (51% o2max) were achieved within the first 5 minutes of exercise and were maintained for the duration of the training session.

In terms of caloric expenditure, as a group men expended more calories than women, but there was no significant difference between the sexes when caloric expenditure was expressed relative to body weight. For the group, the average caloric expenditure was 0.14 kcal·kg−1·min−1, resulting in an average expenditure of approximately 289 kcal for the 28.5-minute CFE bout. The mean expenditures in kilocalories per minute for women, men, and the group were 8.3, 12.0, and 10.2, respectively. This is higher than the caloric expenditure reported in studies examining either traditional resistance exercise (3) or circuit weight training (2,19), which found energy expenditures ranging from 5 to 9 kcal·min−1. As with oxygen uptake values, the higher energy expenditure values seen in the present study are likely related to the large amount of muscle mass involved in the functional activities. In addition, there was a modest energy contribution from anaerobic glycolysis, suggested by the post lactic acid concentration of 4.5 mmol·L−1 and the pre- to postexercise change in lactic acid concentration of 2.5 mmol·L−1. One circuit weight training study reported post lactate values of 8.8 mM (8), and another reported a post lactate value of 17 mM (12). Although the values from the present study are lower than those from circuit weight training, the post lactate value suggests blood lactate accumulation may be elevated enough to cause some muscle discomfort. As with circuit weight training, the lactate values after CFE are likely attributable to use of small muscle groups during exercise performance. These smaller muscles typically develop a high level of intramuscular pressure, restricting blood flow and causing the active muscle to depend in part on anaerobic metabolism (8,11,12).

The average percentage of HRmax achieved during the CFE workout was 83%. As in many studies examining resistance exercise and circuit weight training, the heart rate response was disproportionate to the oxygen consumption (2,8,11,12). Previous studies have attributed this elevated heart rate response during exercise engaging upper-body muscle mass to increased static muscular load, which can restrict venous return and reduce stroke volume (2,20). In this situation, heart rate may increase independently of oxygen uptake to maintain cardiac output. Approximately 95% of the exercises performed in the functional exercise workout required upper-body muscle mass to move the resistance. Thus, it is not recommended that heart rates from the CFE workout be used as valid indicators of cardiovascular intensity.

In summary, the results of this investigation indicate that CFE resulted in energy expenditure, but not oxygen uptake values, which meet the ACSM recommendations. In comparison with circuit weight training, CFE elicits higher oxygen uptake and energy expenditure values. This investigation examined a single, acute bout of CFE and, thus, could not assess changes in cardiovascular fitness, muscular strength, or endurance. In addition, our study was limited in that we did not measure mode-specific maximal oxygen uptake or assess the amount of space covered or core engagement during the exercises. Future research should examine the impact that these factors may have on oxygen uptake during functional exercise and the potential benefits of chronic participation in CFE to examine the cardiovascular and muscular fitness adaptations to CFE training. A training study that evaluates potential muscular strength and endurance adaptations from traditional resistance exercise and that compares them with those from functional exercise would be very useful.

Practical Applications

Although the CFE workout examined in this investigation did not result in oxygen uptake values that meet ACSM recommendations for improving cardiovascular fitness, it did meet the ACSM guidelines for energy expenditure, with a mean of 289 kcal for 28.5 minutes of exercise. Thus, CFE would be a reasonable cross-training option for individuals interested in weight loss or improving their overall health, and it can offer variety in an exercise program. Personal trainers may find that offering functional exercise in this format is desirable because it can be taught as group exercise, which is preferred by some participants and can maximize profits for trainers.

Acknowledgments

The authors thank Mitch Smith, certified personal trainer, for his help in developing and performing the functional resistance exercise routine used in this investigation.

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Keywords:

energy expenditure; cardiorespiratory response; oxygen uptake

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