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Physiological Changes with Periodized Resistance Training in Women Tennis Players

KRAEMER, WILLIAM J.1; HÄKKINEN, KEIJO6; TRAVIS TRIPLETT-MCBRIDE, N.3; FRY, ANDREW C.3; PERRY KOZIRIS, L.3; RATAMESS, NICHOLAS A.1; BAUER, JEFFREY E.3; VOLEK, JEFF S.1; MCCONNELL, TIM4; NEWTON, ROBERT U.2; GORDON, SCOTT E.3; CUMMINGS, DON5; HAUTH, JOHN5; PULLO, FRANK5; MICHAEL LYNCH, J.3; MAZZETTI, SCOTT A.2; KNUTTGEN, HOWARD G.3

Medicine & Science in Sports & Exercise: January 2003 - Volume 35 - Issue 1 - p 157-168
APPLIED SCIENCES: PHYSICAL FITNESS AND PERFORMANCE
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KRAEMER, W. J., K. HÄKKINEN, N. T. TRIPLETT-MCBRIDE, A. C. FRY, L. P. KOZIRIS, N. A. RATAMESS, J. E. BAUER, J. S. VOLEK, T. MCCONNELL, R. U. NEWTON, S. E. GORDON, D. CUMMINGS, J. HAUTH, F. PULLO, J. M. LYNCH, S. A. MAZZETTI, and H. G. KNUTTGEN. Physiological Changes with Periodized Resistance Training in Women Tennis Players. Med. Sci. Sports Exerc., Vol. 35, No. 1, pp. 157–168, 2003.

Purpose To compare the physiological and performance adaptations between periodized and nonperiodized resistance training in women collegiate tennis athletes.

Methods Thirty women (19 ± 1 yr) were assigned to either a periodized resistance training group (P), nonperiodized training group (NV), or a control group (C). Assessments for body composition, anaerobic power, V̇O2max, speed, agility, maximal strength, jump height, tennis-service velocity, and resting serum hormonal concentrations were performed before and after 4, 6, and 9 months of resistance training performed 2–3 d·wk−1

Results Nine months of resistance training resulted in significant increases in fat-free mass; anaerobic power; grip strength; jump height; one-repetition maximum (1-RM) leg press, bench press, and shoulder press; serve, forehand, and backhand ball velocities; and resting serum insulin-like growth factor-1, testosterone, and cortisol concentrations. Percent body fat and V̇O2max decreased significantly in the P and NV groups after training. During the first 6 months, periodized resistance training elicited significantly greater increases in 1-RM leg press (9 ± 2 vs 4.5 ± 2%), bench press (22 ± 5 vs 11 ± 8%), and shoulder press (24 ± 7 vs 18 ± 6%) than the NV group. The absolute 1-RM leg press and shoulder press values in the P group were greater than the NV group after 9 months. Periodized resistance training also resulted in significantly greater improvements in jump height (50 ± 9 vs 37 ± 7%) and serve (29 ± 5 vs 16 ± 4%), forehand (22 ± 3 vs 17 ± 3%), and backhand ball velocities (36 ± 4 vs 14 ± 4%) as compared with nonperiodized training after 9 months.

Conclusions These data demonstrated that periodization of resistance training over 9 months was superior for enhancing strength and motor performance in collegiate women tennis players.

1Human Performance Laboratory, University of Connecticut, Storrs, CT;

2School of Biomedical and Sports Science, Edith Cowan University, Joondalup, WA, Australia;

3Laboratory for Sports Medicine, The Pennsylvania State University, University Park, PA;

4Geisinger Medical Center, Danville, PA;

5East Stroudsburg University, East Stroudsburg, PA; and

6Neuromuscular Research Center, Department of Biology of Physical Activity, University of Jyväskylä, Jyväskylä, FINLAND

Address for correspondence: William J. Kraemer, Ph.D., FACSM, Human Performance Laboratory, Department of Kinesiology Unit-1110, University of Connecticut, Storrs, CT 06269-1110; E-mail: kraemer@uconnvm.uconn.edu.

Submitted for publication January 2002.

Accepted for publication July 2002.

The classical model of periodization of resistance training manipulates the intensity and volume of exercise over time with the intent to minimize boredom, prevent overtraining, and reduce injuries (25). Typically, it was used by strength/power sports to peak physical performance for major competitions. However, not all sports are pure strength/power sports, and many sports have multiple competitions and long seasons. Therefore, a nonlinear or undulating model has been proposed for use so that different training sessions can be rotated over a 7- to 10-d cycle (3,27). To date, although the theoretical basis of such training theory is well established, few data exist regarding its efficacy in comparison with the more traditional multiple-set resistance-training programs (12). Thus, there is a distinct need for research in this area of study, especially in women athletes.

A recent review of the literature supported the hypothesis that periodization of resistance training can result in greater maximal strength gains and may even result in greater motor performance adaptations when compared with traditional resistance-training programs with limited variation in the stimuli over long-term periods (11). Many resistance-training programs provide limited variation in the intensity and volume used (11). Furthermore, limited data are available in female athletes, especially over long-term training periods. It has been shown that female athletes respond favorably to long-term (i.e., 6 months) resistance training (4). Due to the importance of muscular power in the game of tennis, resistance training has become an important training tool to optimize the neuromuscular performance factors related to the primary strokes (20). Yet, no study has evaluated the potential advantage of using a periodized resistance-training program in women tennis players compared with a more traditional multiple-set program consisting of constant resistance and volume. Therefore, the purpose of this investigation was to examine whether nonlinear periodization of resistance training resulted in additive performance or physiological adaptations compared with a traditional resistance-training program performed in the context of an academic year in collegiate competitive women tennis players. Assessments of muscle strength, power, agility, speed, tennis ability, aerobic capacity, jumping ability, body composition, and resting hormonal concentrations were used to determine the effectiveness of the programs and to present a comprehensive view of such training in women tennis players.

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METHODS

Experimental design and approach to the problem.

To investigate the primary hypothesis of this study, we utilized a longitudinal research design, which allowed comparisons of two different resistance-training programs over 9 months (e.g., nonlinear periodized and nonperiodized). The nonlinear periodization model involved rotation of the training intensity and volume of exercise in a given week. Such nonlinear variation of training intensity has been proposed to be more conducive to sports with multiple competitions and longer seasons (27). In addition, the variation in the volume of exercise was greater in the nonlinear periodized program; however, the total training volume (i.e., number of sets multiplied by the number of repetitions performed) during each week was similar to the traditional resistance-training program. This was critical to study design as differences in the overall training volume between programs have been proposed to influence performance adaptations (3,11,34). Thus, we were able to examine the influence of nonlinear periodized resistance training on physical performance and physiological adaptations while avoiding the confounding effect of total training volume.

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Participants.

Thirty collegiate women tennis players from three universities, who were not currently involved in resistance training, were medically screened before the investigation and had no medical or orthopedic problems that would compromise their participation in the study (Table 1). Before testing, participants signed informed consent documents approved by the University’s Institutional Review Board for the Use of Human Subjects consistent with policies of the American College of Sports Medicine. Participants were matched based on their ranking in the United States Tennis Association (USTA) and were randomly placed into one of three groups: 1) nonlinear periodized resistance training (P, N = 9); 2) nonperiodized resistance training (NV, N = 10); or a control group not involved in any resistance exercise but who continued to perform regular activities associated with tennis practice (C, N = 8). Three women did not complete the study due to schedule demands, yielding complete data set from 27 women. Competitive tennis experience was similar among groups (8.1 ± 3.5 yr). No differences were observed among women’s groups in any experimental test variables before training.

TABLE 1

TABLE 1

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Experimental testing.

Participants were initially tested for body composition; anaerobic power; aerobic capacity (V̇O2max); speed and agility; grip strength; jump height; one-repetition maximum (1-RM) leg press, bench press, and shoulder press; ball velocities for the serve, forehand, and backhand tennis strokes; and serum insulin-like growth factor-1 (IGF-1), testosterone, sex-hormone binding globulin (SHBG), and cortisol concentrations. All women then participated in a 9-month study including collegiate tennis practice/play and resistance training (P and NV groups only) and were retested after 4, 6, and 9 months. All women were carefully familiarized with all testing and training protocols and procedures to eliminate acute learning effects (10). The tests utilized in this investigation demonstrated exceptional test-retest reliability with intraclass correlation coefficients ranging from 0.91 to 0.99. All tests were performed at the same time of day to reduce the impact of any diurnal variations. Participants were asked to maintain their same dietary and activity habits for 48 h before testing.

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Anthropometry and body composition.

Height (cm) and body mass (kg) were determined with a physician’s scale. Skinfold measurements were obtained from three sites (triceps, suprailiac, and thigh) on the right side of the body by the same investigator using a Lange skin-fold caliper (Country Technology, Gays Mills, WI). The average of two skinfold thicknesses within 2 mm was used as the skinfold value. Body density was subsequently estimated using the equation described by Jackson et al. (15), and percent body fat was determined using the value obtained for body density and the Siri equation (15,30). Fat-free mass (kg) was then calculated by subtracting fat mass from body mass.

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Anaerobic power.

After a 2-min warm-up using zero resistance, a modified 30-s Wingate cycle ergometer power test using a Monark Cycle Ergometer (Recreation Equipment Unlimited, Inc., Pittsburgh, PA) was performed to determine peak power output. Seat height was determined by a 10° right-knee angle when the right foot was in the pedal down position with the participant seated on the bike. The ergometer load setting was calculated as the participant’s body weight multiplied by a factor of 0.075. The participants were verbally encouraged to pedal as fast as possible throughout the entire 30-s test. Pedal revolutions were digitally counted throughout the test and recorded after each 5-s time frame. Peak power output (W) was then calculated according to previously established methods (16).

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Aerobic capacity (V̇O2max).

Maximal oxygen consumption (V̇O2max) was determined using a graded exercise test to volitional fatigue and/or attain of maximal heart rate with a modified Bruce protocol on a Quinton® (Seattle, WA) motorized treadmill (7). Oxygen consumption and carbon dioxide production was monitored via an online breath-by-breath computerized indirect spirometry with oxygen and carbon dioxide analyzers (Applied Electrochemistry S3A and CD3A Ametek Thermax Instrument Division, Pittsburgh, PA), and heart rates and ratings of perceived exertion were obtained for each minute of the test (36). Expired gases were closely monitored during the last 6 min of the test using an automated metabolic system using classical end points for determination identical to our prior work (21).

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Sprinting speed and agility.

Ten- and 20-m sprint times were obtained from a standing start using two photoelectric cells (Model ET3, Catalogic Optic Electronics, Cary, NC) adjusted to the hip level and connected to an automatic timing device (Automatic Performance Analyzer Model 741, Dekan Timing Devices, Carol Stream, IL). The photoelectric cells were positioned at the start and finish lines. The fastest time observed over three trials was recorded for each displacement.

A lateral agility test using regulation-sized tennis racquets modified from a USTA agility test protocol (33) was performed by each woman. Two weighted poles were positioned 2.44 m from the net. A tennis ball was suspended from each pole to hang at approximately waist level and to allow for 360° rotation after contact with the racquet. The distance between the tennis balls was 8.24 m on a horizontal line, which was parallel to the net. Participants began the test on the point halfway between the tennis balls and 12 m from the net. Two directional lights were placed behind the net and in full view at the baseline. The lights were attached to a delayed timer, which was controlled by the same investigator to prevent false starts. Participants were instructed to start from the center mark (equal distance of 4.12 m from both suspended tennis balls) on a horizontal line with the two balls. Upon illumination of either directional light, the participants were instructed to sprint first to their forehand side, make racquet contact with the ball, then sprint to their backhand side and make racquet contact with the ball, then immediately repeat this sequence a second time. Elapsed time was recorded from the time of illumination to the time of racquet contact of the second backhand. Each participant completed three trials, the fastest trial being used for analysis.

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Muscle strength.

Isometric handgrip strength was performed using a Jaymar model 30 J4 (Country Technology) handgrip dynamometer. The dynamometer was adjusted to the participant’s hand and the best of three maximal trials from each hand was used in data analysis.

1-RM strength was determined for a seated machine leg press, and free-weight bench press and shoulder press exercises according to the following methods described by Kraemer et al. (18). Two warm-up sets of 2–5 repetitions at approximately 50 and 80% of perceived 1-RM were performed separated by a 1-min rest interval. Three-to-four attempts separated by 3- to 5-min rest intervals were then performed until a 1 RM was attained. The same investigator during all tests judged successful 1-RM attempts, including complete range of motion of the exercise, for each individual.

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Vertical jump height.

Participants performed three countermovement vertical jumps and started each jump with both hands at eye level and the knees unlocked, and utilized a two-foot take-off with no approach steps permitted. Jump performance was assessed with a Vertec vertical jump tester (Sports Imports, Inc., Columbus, OH). Standing reach was determined while each participant stood flat-footed and reached maximally with the dominant hand. Trials were performed in triplicate and the highest vertical jump height (total jump height − standing reach) was recorded.

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Ball velocities.

The methods used to analyze the ball velocities during the serve, forehand, and backhand strokes have been previously described in detail (20). Briefly, two Panasonic 60-Hz model AG-450 video cameras were positioned facing each other along the baseline of the testing court. A line perpendicular to the camera along the center hash mark of the court was used as a reference plane, and a meter stick was recorded in the plane to determine a scale factor. After warming up, each participant performed the serve, forehand, and backhand until 10 acceptable strokes of each were filmed. An acceptable stroke was accomplished by hitting a ball into the singles’ court for ground strokes, and into the deuce court for right-handed players and the ad court for left-handed players. Participants were instructed to hit all of their shots as hard as possible and along the reference plane.

Ballvelocity values were determined by digitizing trials and analyzing frame-by-frame with the Peak 2D Motion Analysis system (Peak Performance Technologies, Englewood, CO). Three frames before impact, the impact frame, and three frames after impact were digitized for each trial. The data were expanded to represent collection at 240 Hz using a cubic spline interpolation routine without smoothing. During analysis, the researcher disqualified trials that did not appear maximal. Other possible disqualifying factors included balls hit at an acute angle relative to the reference plain or if a portion of the stroke occurred outside the field of view of the camera. The average ball velocity of the top three trials for each stroke was used as the value.

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Biochemical analyses.

Resting venous blood samples were obtained from a superficial arm vein using a needle, syringe, and Vacutainer setup with the participant in a slightly reclined, seated position. Women in the study had normal menstruation with a similar percentage of women in each group who were taking oral contraceptives. Resting venous blood samples were obtained from the women during the early follicular phase of the menstrual cycle, and blood was obtained at the same time of the day for each woman to reduce any possible effects of hormonal diurnal variations. Whole blood was processed, and serum samples were stored at −85°C until analyses were performed.

Total IGF-1 was analyzed in duplicate using a 125I liquid-phase double-antibody radioimmunoassay (RIA) with an octadecasylyl-silica preliminary column (acid-methanol) extraction to separate IGF from its binding proteins (IncStar, Stillwater, MN). Testosterone and cortisol were measured in duplicate using 125I solid-phase RIAs (Diagnostic Products, Los Angeles, CA). SHBG concentrations were determined in duplicate using a double antibody, liquid phase 125I RIA (Diagnostic Products). Intra- and inter-assay variances were between 2.0 and 5.0%. Immunoreactivity was measured with an LKB 1272 Clinigamma automatic gamma counter and on-line data reduction system (Pharmacia LKB Nuclear, Turku, Finland). Samples were thawed only once for analyses.

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Resistance-training programs.

Resistance exercise selection and order were identical between the two training programs (Table 2) and each group performed two-to-three sets of each separated by a 1.5- to 2-min rest intervals. Heavier loads (4–6 RM) required 3-min rest periods for optimal recovery. The C group participated in all tennis training and conditioning drills but did not perform any heavy resistance exercise. Subjects in the P and NV groups were individually supervised by an experienced personal trainer to ensure that all essential program characteristics were strictly enforced. Most important, the trainers in the study were responsible for the progression of training loads. It has been recently demonstrated that direct supervision of resistance training enhances strength performance adaptations via greater and faster training load progression (26). In either group, when a participant was capable of performing the required number of repetitions for three consecutive sets of a particular exercise, the training load was increased in increments of about 2–13 kg, depending on the absolute load being used. Both groups performed three workouts per week with one rest-day between sessions unless match play allowed only two per week. Complete (100%) attendance for all workouts was observed as make-up sessions were allowed.

TABLE 2

TABLE 2

Numbers of repetitions were preliminarily designed according to each specific training program and are shown in detail in Table 2. Because differences in training volume between resistance-training program designs have been proposed to influence maximal strength performance adaptations, the total number of sets multiplied by repetitions per week was equated between the P and NV training program designs (total sets × repetitions ≈ 830) (3,11,34). Thus, the major difference between the two programs was that the P group rotated loading schemes (4- to 6-RM with longer rest intervals, 8- to 10-RM, and 12- to 15-RM) over successive workouts on Monday, Wednesday, and Friday, respectively, whereas the NV group utilized a traditional moderate-intensity loading scheme (8- to 10-RM) where the relative intensity remained constant. It is crucial to note that within our study design, it was not conducive to include an additional nonperiodized, high-intensity (4- to 6-RM) resistance-training group due to various concerns associated with such uninterrupted, long-term heavy-resistance training in actively competitive women tennis athletes (e.g., injury, overtraining, etc.) (12). Another possible group, nonperiodized, low-intensity (12- to 15-RM) resistance training, was not used due to limitations in the number of competitive athletes available. Thus, the comparison is essentially one of similar volume with planned multiple loads to a program with only a single load training zone over time.

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Statistical analyses.

Data are presented as the mean ± SD. Statistical analyses for each dependent variable were accomplished with a separate two-way ANOVA with repeated measures. When a significant F-ratio was achieved, post hoc comparisons were accomplished via a Fisher’s least significant difference test. Statistical power for the various dependent variables examined ranged from 0.72 to 0.92 for the sample sizes used at the 0.05 alpha level (nQuery Advisor® software, Statistical Solutions, Saugus, MA). Significance in this study was defined as P ≤ 0.05.

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RESULTS

Body composition.

Fat-free mass increased and percent body fat decreased significantly after P and NV training, but no differences were observed among groups in any of the body composition variables at any time point (Table 3). Despite the lack of differences in body composition between groups, there was a trend (P = 0.09) for an interaction in fat-free mass values over time. Also, the absolute change (mean Δ ± SD) in fat-free mass over the 9 months was significantly greater in P (3.3 ± 1.7 kg) than NV (1.6 ± 2.4 kg).

TABLE 3

TABLE 3

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Anaerobic power and V̇O2max.

Peak anaerobic power increased significantly after 9 months in P and NV (Table 4). Peak power was significantly greater in the P group than the NV group after 4 and 6 months of training, but anaerobic power values were similar between the two groups after 9 months. Surprisingly, V̇O2max decreased significantly after 9 months in P and NV. However, no differences were observed among groups in V̇O2max at any time point.

TABLE 4

TABLE 4

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Speed, agility, and vertical jump.

Sprinting speed and agility did not change after P and NV training and no differences were observed among groups in 10-m or 20-m sprinting speed or agility at any time point (Table 5). Maximal countermovement jump height increased significantly during both P and NV training, but the percent increase in jump height after 9 months was significantly greater after periodized resistance training (≈50% vs 37%;Fig. 1). As a result, jump height was significantly greater in the P group than the NV group after 9 months of training.

TABLE 5

TABLE 5

FIGURE 1

FIGURE 1

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Muscle strength.

Dominant and nondominant handgrip strength increased significantly during P and NV training (Table 6). No differences were observed between the P and NV groups in grip strength at any time point. 1-RM leg-press performance increased significantly during 9 months of P (19%) and NV (17%) training, but the percent increase after 4 months was significantly greater during periodized resistance training (9.3% vs 4.5%;Fig. 2). 1-RM bench press performance increased significantly after 9 months of P (23%) and NV (17%) training, but the percent increase after 6 months was significantly greater during P training (≈22% vs 11%;Fig. 3). In terms of absolute 1-RM bench press performances, the P group was significantly greater than the NV group after 4 and 6 months of training. 1-RM shoulder press performance increased significantly after 9 months of P (24%) and NV (23%) training, but the percent increase after 6 months was significantly greater during P (≈24% vs 18%;Fig. 4).

TABLE 6

TABLE 6

FIGURE 2

FIGURE 2

FIGURE 3

FIGURE 3

FIGURE 4

FIGURE 4

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Ball velocities.

Ball velocities for all three tennis strokes increased significantly during both P and NV training, but the percent increases in the tennis serve (≈29% vs 16%), forehand stroke (≈22% vs 17%), and backhand stroke (≈36% vs 14%) after 9 months were each significantly greater after P (Figs. 5–7).

FIGURE 5

FIGURE 5

FIGURE 6

FIGURE 6

FIGURE 7

FIGURE 7

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Hormonal concentrations.

Resting serum concentrations of IGF-1, testosterone, and cortisol increased significantly during both P and NV training (Table 7). Resting serum concentrations of IGF-1 and cortisol were also significantly increased in the C group, suggesting an influence of collegiate tennis practice and competition on adaptations in the endocrine system (Table 7). Resting serum cortisol concentrations were significantly greater in the P group than both the NV and C groups after 4 and 9 months of training but not after 6 months (only greater than the C group).

TABLE 7

TABLE 7

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DISCUSSION

The primary findings of this investigation were that periodization of resistance training did produce greater magnitudes of improvements in strength and sport-specific motor performances than a traditional resistance-training program in collegiate women tennis players. Such differential adaptations in strength and power between the two training programs most likely contributed to greater improvements in jump height and ball velocities for the serve, forehand, and backhand tennis strokes. Furthermore, these differential adaptations between periodized and traditional progressive resistance-training groups occurred despite similar weekly training volumes, indicating the inclusion of variation as an important factor in a training program. In the past, it has been argued that the greater strength gains typically observed after periodized resistance-training programs were mediated by reductions in the training volume (i.e., tapering the number of sets and repetitions) (3,11,34). Thus, to our knowledge, these data are the first to demonstrate greater strength and motor performance gains in women athletes using similar volumes of exercise.

Because the variation of intensity during each week of periodized training was the major difference between the two training program designs, this appears to be the mediating factor in the additive effects observed in strength and power using this nonlinear periodized training strategy. This was most likely due to the ability to recruit more fast-twitch motor units with the inclusion of the heavier loading (i.e., 4–6 RM) (13,28,29). Training studies in men have shown that individuals exposed to heavier loads during training experienced greater improvements in maximal strength performance (2,9,10). The use of heavy resistance training was also shown to be effective for increasing strength in women athletes over 6 months (4). Therefore, variation in training intensity in the periodized resistance-training program to accommodate the rigors and schedule demands of tennis practice and competition was an effective method to facilitate the underlying neuromuscular and performance adaptations.

Although our data can only indicate the potential for other factors to be involved with the differential training effects among groups, both muscle hypertrophy and endocrine factors could produce such integrated effects. In the present study, the change in fat-free mass over 9 months tended to be greater in the P group (P = 0.08) than the NV group, reflecting enhanced body composition and muscle hypertrophy with periodized resistance training (3,35). Other training studies in women have demonstrated significant body composition changes in fat-free mass while reporting increases in strength performance similar to those reported in the present study (5,6,8). It appears the differential strength adaptations between periodized and traditional multiple-set resistance training may be due to a combination of neurological and muscular adaptations (28,29,31,32).

It is well documented that women’s upper-body strength differs from their lower-body strength in terms of initial strength levels and training adaptations (24,35). Wilmore (35) had demonstrated that women’s relative upper-body strength (i.e., in relation to fat-free mass) remains much less than men’s after 10 wk of training, whereas their lower-body strength relative to fat-free mass may equal or even surpass that of men’s. Classically, this has been indicative of the difficulty of making the same magnitude of gains in women’s upper body as observed in their lower body or in comparison with men. The majority of the strength gains in 1-RM bench-press performance occurred during the first 4 months in the P group in the present study. A similar plateau trend was also observed in the 1-RM shoulder press after six months in the P group. The inability to continually improve over the entire training program may have been limited by the upper limits of physiological adaptation possible during this time period in these competitive women tennis players. Of significance to the adaptational time course was the fact that the last 3.5 months of training were performed within the context of a competitive tennis season. This may have also influenced the magnitude of gains made in the upper body of these women. Conversely, in contrast with the upper-body adaptations was the ability of the lower body to continue to significantly increase strength and power over the entire training program in the P group. Such data demonstrate that there may be a need for further study of periodized training strategies specifically for the upper body in women.

From a sports-specific conditioning perspective, the observed findings of significantly improved ball velocities for the serve, forehand, and backhand tennis strokes in the P and NV groups demonstrated the importance of resistance training for sport. The greater magnitude of improvement observed after periodized resistance training supports the use of such a training strategy. In the present study, both training groups significantly increased 1-RM shoulder press and ball velocities. In addition, periodized resistance training induced small but significant continued improvements in ball velocities over the 9-month period, whereas nonperiodized training did not. It is possible that resistance training increased upper-body force production capabilities sufficiently to enable a better transfer into power and high-velocity force production necessary during the different tennis strokes (23,37). The increases in maximal strength in the shoulder musculature were important. Kraemer et al. (20) have previously reported that strength and joint laxity were the only significant contributors to ball velocities of different tennis strokes with the 1-RM shoulder press being more highly correlated (R = 0.69) to three ball velocities than the bench press (R = 0.30) (20). This indicates that the strength of the deltoids appears more important to the development of higher ball velocities than the pectoralis muscles of the chest. Nevertheless, a total sports-specific tennis-training program was used which ultimately contributes to the over all development of the neuromuscular capabilities needed in the sport.

It is interesting to note that lower-body strength performance increased over the entire 9-month experimental period. Because tennis strokes are dependent upon the entire closed kinetic chain of muscle, greater enhancements in hip and lower-body force/power production capabilities (i.e., 1-RM leg press, vertical jump) may also have contributed to the larger improvements in ball velocities during tennis strokes in the P group. It may be speculated that potential mediating mechanisms may be related to greater activation and synchronization of high force/power motor units, which have a higher recruitment threshold and/or enhanced inhibition of antagonist muscle activity (23,28,29). The inclusion of heavy training (4–6 RM) may have played an important role in the program design.

The interaction of different physical performance capabilities with training and competitive tennis remains complex. Tennis-induced upper-body strength imbalances have been documented in non-resistance-trained, collegiate women tennis players (20). Although no differences were observed between the P and NV groups, isometric grip strength did increase significantly in both groups, resulting in a diminishment of the imbalance between dominant and nondominant handgrip strength. The speed and agility results demonstrate that, despite the evident influence of resistance training on sport-specific motor performance, there is a much greater need for specific “speed training” beyond what would be inherent to typical tennis conditioning drills and strength training programs. Thus, more specialized training is necessary beyond resistance training if speed improvements are a training goal in competitive athletes. Interestingly, adaptations in peak anaerobic Wingate power output resulted in greater performances in the P group than the NV group after 4 and 6 months of training, but these differences were diminished after 9 months of training within the context of a competitive season. These data indicate the difficulty in continually improving during the rigors of a competitive season and may demonstrate the importance of maintenance training during this time. Surprisingly, aerobic power (V̇O2max) decreased in the two resistance training groups over the last 3 months of training during the major competitive season. The interplay between anaerobic and aerobic development and competitive tennis remains complex, but with the game focused on power and very short points, anaerobic power may be more important. Thus, our data appear to indicate that when peak anaerobic power is improved, aerobic capacity may be somewhat reduced due to a change in the priority of the body’s adaptations to higher force generation and toleration of glycolytic exercise metabolism (21). This may be especially true in tennis where “burst-like” power capabilities represent the new trend in the game of tennis. These data demonstrate the dramatic need for training programs, which are designed using the concepts of “specificity of training” relative to the desired sports-specific fitness goals of athletes (12).

The endocrine system underlies many of the physiological mechanisms of adaptation with resistance training (19). The changes in the resting concentrations of IGF-1, testosterone, and cortisol over the 9-month period reflected a variety of external stimuli including the influences of resistance training, tennis practice, and tennis competition that influenced the body’s environment. Some of these hormonal changes, in particular the increases in IGF-1 and small increases in testosterone concentrations during resistance training, may have helped to mediate observed adaptations in muscular performances and fat-free mass during both the P and NV training programs. In view of the proposed role(s) of these hormones in the hypertrophy of skeletal muscle (1,18), our data support an influence of resistance training and concomitant tennis conditioning on women’s resting hormonal concentrations over 9 months. The changes in resting IGF-1 concentrations also increased over the final 3 months in all groups (including the C group) showing that the stresses of training and/or a competitive season can influence hormonal mechanisms at the level of the circulation. These findings for IGF-1 are similar to the results recently reported by Koziris et al. (17), who also demonstrated that total and free resting IGF-1 concentrations, as well as IGF binding protein-3, were significantly enhanced with strenuous swim training over 6 months in women and men. Thus, strenuous training associated with collegiate tennis conditioning, especially the competitive season, appears to influence the neuroendocrine system sufficiently to require adaptive changes. Such changes in IGF-1 physiology may also occur locally to help mediate the changing needs of the muscle fibers and bone during strenuous training and sport competition (1,17,18).

The influence of the stress of tennis play and practice on the endocrine system was also evident in the cortisol results because increases occurred in all groups over the 9 months. Resting serum concentrations of cortisol in women have shown no difference after 16 wk of power training (14) and have shown decreases after 8 wk of high-volume resistance training (22). We had hypothesized a reduction in cortisol following resistance training in both groups, but it appears that tennis practice and competition have a greater influence on cortisol production than what can be off-set by a resistance-training program alone. The P group had a greater cortisol response that may have reflected a higher overall stress with the greater exposure to heavier lifting. The trophic influence of SHBG remained relatively stable yet the adrenal cortex appeared more sensitive in the P group after the first 3 months. Nevertheless, it remains unclear how the interaction of cortisol at the level of the receptor is affected by training. It may be that a reduction in the binding sites might be observed in the resistance training groups, which would mitigate any negative effects (e.g., protein degradation, immune suppression) of the higher cortisol concentrations being produced after the first 3 months of training, practice, and initial competitions. Thus, future study at the receptor level of cells remains important to improve our understanding of circulatory endocrine changes. These data do show that over a long-term resistance-training program and/or rigorous collegiate tennis training/competition program, hormonal adaptations become observable at the level of the circulation.

In summary, this investigation examined the additive effects of periodized resistance training on performance and hormonal adaptations in women tennis players. The results demonstrated that there are distinct differences between periodized and nonperiodized training programs. These differences are evident in both the rate of the observed adaptations as well as in the magnitude of changes. It appears that the use of a heavier resistance-training session rotated into a training sequence of different intensities may be essential for optimizing muscular force, endocrine, and performance adaptations. Although further work is obviously needed in this area of study (11), this is the first long-term study that has demonstrated that one style of periodization of resistance training can elicit significantly greater increases in lower- and upper-body 1-RM strength and motor performances in women tennis players. This gives important support to the hypothesis that periodization (variation in training) may be essential for optimization of resistance-training programs in women.

We would like to thank our dedicated subjects and a large group of research assistants. This study was supported in part by a grant from the United States Tennis Association, Key Biscayne, FL (USTA Grant to WJK). In addition, we would like to thank all of the laboratory staff and trainers who helped with the testing and training of these subjects, Jeff Connors for his help in the strength training programs and the various tennis coaches and athletes, including Coach Sue Whiteside, for their support.

Current addresses: Jeffrey A. Bauer, State University of New York College at Cortland, Cortland, NY, L. Perry Koziris, Department of Kinesiology, University of North Texas, Denton, TX. Andrew C. Fry, Ph.D., University of Memphis, Travis Triplett-McBride, Ph.D., Department of Exercise Science, University of Wisconsin-LaCrosse, LaCrosse, WI, J. Michael Lynch, Quincy University, Quincy, IL, and Howard G. Knuttgen, Harvard University, Cambridge, MA.

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Keywords:

NONLINEAR VARIATION; WOMEN’S HEALTH; MOTOR PERFORMANCE; TRADITIONAL STRENGTH TRAINING

©2003The American College of Sports Medicine