Dry-Land Strength Training vs. Electrical Stimulation in Sprint Swimming Performance : The Journal of Strength & Conditioning Research

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Original Research

Dry-Land Strength Training vs. Electrical Stimulation in Sprint Swimming Performance

Girold, Sébastien; Jalab, Chadi; Bernard, Olivier; Carette, Pierre; Kemoun, Gilles; Dugué, Benoit

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Journal of Strength and Conditioning Research: February 2012 - Volume 26 - Issue 2 - p 497-505
doi: 10.1519/JSC.0b013e318220e6e4
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Abstract

Introduction

In swimming, performance depends on many factors wherein some technical and physiological factors play a predominant role. For distances ranging from 50 to 200 m, the propulsive efficiency has a major impact on performance (51). This efficiency is mainly because of the involvement of muscle contractile qualities and muscle strength of the upper limbs (24,43). The lower limbs only participated very slightly (∼12%) in the propulsion of the swimmer (30,49).

Several conditioning training methods using swim bench, weight training, or in-water resistance have been described to improve swimmers' physical abilities (8,18,48). At high levels of practice and ability, program efficiency mainly depends on the training session intensity (4,37) and the specificity of the coming event (33,46).

Generally, gains in sprint performance are consistent within 1.3–4.4% (8,43,48). For example, Strass et al. (48) showed that press and draw exercises with barbells over a 6-week period at a rate of 4 sessions per week and an intensity of 90–100% in relation to 1 maximal repetition led to significant 4.4 and 2.1% increases in performance over 25 and 50 m, respectively. Hawley et al. (24) and Smith et al. (45) demonstrated a strong relationship (r = 0.82 and 0.93, respectively; p < 0.05) between upper body strength with respect to peak torque and sprint swimming performance over 25 yd and 50 m.

Pichon et al. (40) analyzed the effects of a 3-week electrical stimulation training program on the strength of the latissimus dorsi muscle and sprint swimming performance. They observed a significant increase in the peak torque of the arm extensors of, on average, 10–24% at different velocities (from −60 to 360°·s−1). They also observed an increase in sprint swimming performance of 1.3% for arm-stroking with a pull buoy over 25 m and 1.4% over a 50-m freestyle sprint. The increases in peak torque, measured in the eccentric condition (−60°·s−1), were correlated with increased performance. These results show that an electrostimulation program focused on the latissimus dorsi could increase sprint swimming performance.

An electromyography study undertaken by Clarys (6) revealed the extensive involvement of the latissimus dorsi in the front crawl throughout the propulsive phase, in lowering and adducting the arm, and in orienting the propulsive surfaces. This study also demonstrated the importance of the triceps brachii, deltoideus, and teres major muscles.

Surprisingly, although the efficiency of dry-land strength and electrical stimulation training methods on sprint swimming performance are both reported, to our knowledge, no randomized comparative studies have thus far been performed. Moreover, there is currently no information available regarding how long the effects of these training techniques may last.

Thus, the purpose of this study was to compare the effects of a combined dry-land strength training and swimming program with those of a combined electrical stimulation program with the same swimming program and to assess whether the observed effects last after the training period has ended.

In a context of time-consuming training, the addition of short-term effective methods to regular training may be attractive. Although it is believed that the more demanding the training is, the greater the benefit will be, one must also consider the training volume of the athletes in its entirety to avoid overtraining-related disturbances.

Methods

Experimental Approach to the Problem

The main purpose of this study was to investigate whether the dry-land and the electrical stimulation strength training methods were able to enhance the performances of swimmers in the 50-m sprint. It was thus decided to organize exercises such as pull-ups and draws with pulley in dry-land strength training conditions and to use of an electrical stimulation strength training program providing by an electrical stimulator for electrical stimulation strength training.

In dry-land strength training and in electrical stimulation training, short and intensive sets were performed to increase maximal strength and anaerobic power, respectively, and thus to improve sprint abilities over 50 m during a 4-week training period.

Subjects

A group of 24 national-level competitive swimmers (12 men, 12 women; mean ± SD, age 21.8 ± 3.9 years, height 174 ± 8 cm, body mass 66 ± 9 kg, arm span 175 ± 11 cm) took part in this study. The swimmers signed an informed consent form and participated in the study on a voluntary basis. This study was approved by our University Committee on Human Research. Swimmers trained an average of 10 × 2 h·wk−1 in water and an average of 3 × 1 h·wk−1 on dry land based on a specific conditioning program, in the same swimming club, and under the same conditions. Globally, the training volume was around 30 km·wk−1 for each of our swimmers. They were all swimmers sprinters and their personal records in 50 m were 27.8 ± 1.8 seconds (75.5% of world record). They were all French national 1 level swimmers who had been able to maintain their level at least for the last for 4 years.

Procedures

Before randomization, the matching was performed according gender, age, and performance (50-m sprint). Then, swimmers were randomly divided into 3 groups: (a) dry-land strength (S), (b) electrical stimulation (ES), and (c) control (C) groups. The average of best performance (expressed in seconds as mean ± SD) in 50-m freestyle for every group were 26.84 ± 1.90, 28.01 ± 1.27, and 28.57 ± 2.20, respectively. These times correspond to 78.5, 75.25, and 73.78% better world record for this distance; respectively. Each group performed 10 swimming training sessions per week for 4 weeks and the same aerobic dominant work. Normal dry-land training was substituted with an extra dry-land strength training program for the strength group (see below) and with an extra electrical stimulation training program for the electrical stimulation group (see below). The control group did not perform any dry-land training but followed the same swimming training program as the ES and S groups. Therefore, the training volume was exactly the same for S and ES (Table 1).

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Table 1:
Main characteristics of the S, ES, and C groups of French national 1 swimmers and their weekly training volume.*†

The swimmers were asked to follow their usual eating habits and not to add any dietary supplements. They got instructions as to how to behave during the entire study and were asked to keep a diary (to control hydration status, food intake, mood, and the amount of sleep).

This study was carried out far from any important competition and not over a too long period to keep the head coach seasonal training program and to assure the compliance of the swimmers and of their trainer. Moreover, we also wanted to investigate whether the effects of our intervention were maintained afterward. Therefore, we had to consider an 8-week period. Therefore, we decided to carry out this study in a nonspecific macrocycle at the beginning of the second part of the national French swimming season far from important competition and on a relatively short period to allow swimmers to work on other technical and physiological points in the other part of the cycle. In practice, the training program took place in April for 4 weeks, during the second macrocycle of the season. Our athletes were preparing for their national championships in June. During this macrocycle, there were no important competitions, and the strength training intervention ended 6 weeks before the championships.

Description of the Strength Training and Electrostimulation Sessions

The strength training program for S concentrated on increasing the muscular strength of the upper limbs, principally the latissimus dorsi. The strength training sessions were 15 minutes long and were preceded by a 10-minute warm-up using a skipping rope, which was considered as an all-around exercise. There were 3 strength training sessions per week, which were performed on Tuesday, Thursday, and Friday morning 1 hour before the swimming training sessions. The program was the same for each session. The program included 3 sets of 3 exercises with a 2 minutes of rest between each set. A maximum of 6 repetitions was performed for each exercise. The exercises included pull-ups and draws with pulleys. To perform the exercises under the most specific conditions, they were performed with the hand in a pronation grip and the distance between the 2 hands set at shoulder width. The swimmers were instructed to pull on the bar until it reached the level of the chest when performing pull-ups and first draw exercises. For the second draw exercise, swimmers were instructed to pull on the handle until it reached the level of the hips. For pull-ups, the swimmers' own body weight was used as resistance. For the draw exercises, the swimmers were seated on a bench with their legs locked under a bar to avoid any movement of the lower limbs. The intensity of the training varied between 80 and 90% of the maximal load for the draw exercises in relation to the 1RM tests performed before the start of the study. For each repetition, the swimmers were instructed to perform the concentric phase of the movement as fast as possible, maintain a 3-second isometric contraction and return to the initial position by slowing the movement (eccentric phase). The exercise rate was approximately 1 movement every 6 seconds.

The electrical stimulation training program for the ES group was performed at the same time as the strength training program after the same 10-minute warm-up using a skipping rope. The swimmers sat on a bench with their arms along the length of the body and elbows in contact with the trunk to avoid any movements. Electrostimulation was performed with a Compex® Mi Sport 500 (Compex Medical SA, Ecublens, Switzerland). Both latissimi dorsi muscles were simultaneously stimulated. The electrodes used for the electrostimulation were 2 mm thick, self-adhesive, and of the elastomer type. Double-pole stimulation was performed for each latissimus dorsi using 3 electrodes of different surface areas, 2 smalls electrodes of 22 cm2 (4 cm × 5.5 cm), and 1 large electrode of 66 cm2 (12 cm × 5.5 cm). The negative electrode (the large one) was placed 2 finger widths away from its proper anatomically described landmark. The positive electrodes were placed along the spine at a slight angle. To stimulate the paravertebral muscles, these electrodes were placed 2 finger widths from the spinous processes. Pulse currents of 100 Hz in frequency lasting 300 microseconds were used. The contraction time was 5 seconds, and the rest time was 15 seconds. The number of contractions per session was 45, for a total duration of 15 minutes. The intensity of the muscle contraction was controlled by the subjects and was designed to correspond on average to 80–90% of the maximal voluntary contraction according to their sensations.

As previously mentioned, the swimming training program was the same for all 3 groups and consisted of 10 sessions of 2 h·wk−1. These sessions comprised a combination of dominant aerobic work consisting of long sets at a moderate intensity, a short recovery period in the front crawl, and technical work in the medley. The training volume was 6,000 ± 500 m per session.

Swimming Velocity

Swimming velocity was measured before the training program (W0), after 4 weeks (W4) of training, and 4 weeks after the end of the training program (W8). These measurements were performed under the same conditions to evaluate whether the training effects lasted. The measurements were made on the same day of the week and at the same time of the day and were based on a 50-m front crawl, which was performed with a diving start following a starter's instructions, at maximal speed in a 25-m pool and about 15 minutes after a 2,000-m standardized warm-up. The swimmers performed their 50 m one by one, from the slowest to the fastest as it happened in competition, at a rate of approximately one departure every 35–40 seconds. Timing was manual.

Technical Parameters

All 50-m trials were video recorded with a digital cam Sony® miniDV (HDR-HC7, Sony, Japan) at a frequency of 25 Hz. Stroke rate and length were measured with the video analyzer software Pinnacle® (Studio Pinnacle System, Inc, Mountain View, CA, USA). A minimum of 3 complete stroke cycles was analyzed during each 25 m of the 50 m over a distance of 10 m, which corresponded to the field of the camera. The mean of the total number of cycles recorded during the 50 m was used to calculate stroke rate and length. Swimming velocity was calculated based on the stroke length and stroke time ratio. The camera was placed 12.5 m from the edge of the pool such that the recording started 7.5 m after the departure and lasted until 17.5 m of each 25 m to avoid any influence of starting and turning actions on swimming velocity. The camera was placed in a Plexiglas waterproof box (SPKHCC.CE8, Sony, Japan) at a depth of 0.15 m. A ruler designating every meter was placed in the field of the camera at a depth of 0.15 m in the swimmers' lane for calibration.

Muscle Strength Measurements

The extension peak torque (Newton meter) of the dominant arm was measured with an isokinetic dynamometer (CON-TREX®, Medimex Factory, Tassin la Demi Lune, France) at W0, W4, and W8. Before the measurements, a 10-minute standardized warm-up and familiarization period was performed with the apparatus at several submaximal velocities in concentric conditions (60 and 180°·s−1), isometric conditions, and eccentric conditions (−60°·s−1). These different angular velocities were selected because they are most representative for testing swimmers' shoulder torque (35,36). The angular range movement in concentric and eccentric conditions was performed at an average of 160° from the start to the end of the movement. In the isometric condition, the angle between the arm and the trunk was set at 90°. The measurements took place at the end of each week, 24 hours after the last training session. The swimmers laid down and were strapped at the shoulders and pelvis. The arm was maintained parallel to the CON-TREX's arm lever. The spindle of the motor was positioned in line with the center of rotation of the elbow joint. The subjects were asked to perform 5 maximal efforts. The best performance was retained. A 1-minute 30-second rest period separated each test. For the isometric action, the effort lasted 5 seconds, with a 2-minute rest period between repetitions. The angle between the arm and the trunk was set at 90°. Intraclass correlations (Rs) of the physical strength measurements were assessed using a coefficient of variation of 1.9% between 2 measurements.

Body Weight

No changes in the body weight and body composition were observed during the course of the training.

Statistical Analyses

All the results are presented with their mean and SD. The sample size calculation regarding the 50-m test was performed as previously described (18). Using a difference between the groups of 1.0 seconds, an SD of 0.68 seconds, a beta value of 0.80, and an alpha value of 0.05, 6 volunteers per group should be a sufficient number of subjects to detect a significant difference at the end of the training program, should this difference exist.

Analysis of variance (2-way repeated measurements (groups [S, ES, and C] × measures [W0, W4, and W8]) followed by the Tukey-Kramer posthoc test were used to compare the main characteristics, performance, muscular strength, stroke rate, and stroke length, of the 3 groups before and after training. For the whole group, correlation coefficients were calculated between performance and the different parameters measured. The Statistica 5.0 (SAS Institute Inc, Cary, NC, USA) program was used. A p value of 0.05 was considered statistically significant.

Results

Before training (W0), there were no significant differences in swimming velocity, technical parameters, muscular strength, or morphological parameters between the 3 groups (Table 2).

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Table 2:
Swimming performance and arm peak torque characteristics of the S, ES, and C groups of the French national 1 swimmers before the start of the training.*†

Effects of Training on Swimming Velocity

A significant improvement in the mean swimming velocity for 50 m front crawl (p < 0.05) at the end of the training period (W4) was observed in the S and ES groups when comparing the results with those obtained from the same groups at W0 (+2 ± 1.3 and +1.7 ± 0.5%, respectively) and the C group at W0 and W4. At W8, the delayed posttest demonstrated significant improvement (p < 0.05) was still exhibited by both S and ES groups. However, no significant differences were observed between the S and ES groups at any time point. No changes in performance were observed in the C group throughout the study (Figure 1).

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Figure 1:
Changes in performances over 50 m before the training (W0), after 4 weeks of training (W4) and 4 weeks after the end of the training (W8) in French national 1 level swimmers. S = dry-land strength group; ES = electrical stimulation group; C = control groups. *Denotes significance (p < 0.05). Values are expressed as mean ± SE.

Effects of Training on Stroke Length and Stroke Rate

After 4 weeks of training, stroke length was significantly (p < 0.05) increased during the 50 m in S but not in ES and C. At W8, the delayed posttest demonstrated that there was still significant improvement (p < 0.05) in stroke length in S but not in ES and C. There was no significant difference in technical parameter variation, expressed as a percentage of baseline, between the 3 groups after the 4-week training period (Table 3).

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Table 3:
Stroke rate and length in W0, W4, and W8 in the S, ES, and C groups of French national 1 swimmers.*†

Effects of Training on Muscle Strength

After 4 weeks of training, peak torque was significantly (p < 0.05) increased in the concentric condition at 60°·s−1 in S and ES, but not in C. Peak torque was significantly (p < 0.05) increased in the concentric condition at 180°·s−1 in the S and ES but not in C. Peak torque was significantly (p < 0.05) increased in isometric and eccentric conditions at −60°·s−1 in ES but not in S and C. At W8, the delayed posttest demonstrated a significant (p < 0.05) increase in the concentric condition at 60°·s−1 in S and ES but not in C. Peak torque was significantly (p < 0.05) increased in the concentric condition at 180°·s−1 in the S and ES but not in C. Peak torque was significantly (p < 0.05) increased in the isometric and eccentric condition at −60°·s−1 in ES but not in S and C.

When compared with baseline, the increases in peak torque after 4 weeks of training differed in the concentric condition at 60 and 180°·s−1 between S (11.2 ± 13.6%; 16.9 ± 11.7) and C (2.2 ± 7.4%; 1.2 ± 0.7%; p < 0.05), respectively, and between ES (14.8 ± 7.2%; 13.9 ± 5.6) and C (2.2 ± 7.4%; 1.2 ± 0.7%; p < 0.05), respectively, but not between S and ES. When compared with baseline, the increases in peak torque after 4 weeks of training differed in the isometric and eccentric conditions at −60°·s−1 between S (2.7 ± 2.1; 4.6 ± 6.1%) and ES (13.5 ± 10.9; 22.9 ± 6.6%; p < 0.05), respectively, and between ES (13.5 ± 10.9; 22.9 ± 6.6%) and C (1.6 ± 0.9; 6.1 ± 1.5%; p < 0.05), respectively but not between S and C.

Performance variation after the 4 weeks of training, expressed as a percentage of baseline, correlated with stroke length (r = 0.96; p < 0.05) and peak torque in the concentric condition at 60 and 180°·s−1 (r = 0.97; 0.97; p < 0.05) variations in S, but this relationship did not occur in ES and C. In addition, peak torque variations in the eccentric condition at −60°·s−1 (r = 0.99; p < 0.05) occurred in ES but not in S and C.

None of the parameters correlated with performance in C after 4 weeks of training (Table 4).

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Table 4:
Peak torque changes (%) in W4 and W8 in the S, ES, and C groups of French national 1 swimmers.*†

Gender Effect

There was a similar gender percentage in each group, and there were no significant differences in training effects between men and women among the 3 groups.

Discussion

The main findings of this study are as follows: (a) The 2 methods combining swimming and dry-land strength or swimming and ES were more efficient than the swimming program alone in increasing sprint performance. Muscle strength increased in S and ES, whereas stroke length increased only in S. (b) No differences in performance were observed between S and ES. (c) The training effects were maintained 4 weeks after the end of the training program in the S and ES groups.

After 4 weeks of training, no significant differences were observed in performance gain over 50 m between S and ES (Figure 1). The 2% increase in 50-m performance in the S group are comparable with the 2.1% gain reported by Strass et al. (48) over 50 m after a 6-week dry-land (strength) training period and to the 3.6% gain reported by Sharp et al. (43) over 25 yd after an 8-week dry-land (swim bench) training period. The 1.7% increase in 50-m performance in ES are close to the 1.3 and 1.4% gain reported by Pichon et al. (40), who used similar methods of electrical stimulation, for 25-m arm stroking with a pull buoy and the 50-m freestyle, respectively. The S and ES training methods were more efficient for increasing sprint performance than the swimming program alone. These results are in agreement with those previously reported by Pichon et al. (40) and Tanaka et al. (50), indicating that the combination of swimming and dry-land resistance training was more effective than swim training alone for improving swim performance.

The ES group exhibited a stronger increase in eccentric condition than did the S group (Table 4). In the ES group, the 22.9% increase in arm extensor isometric strength is close to the 24.1% gain reported by Pichon et al. (40) after 3 weeks of training. This suggests that ES training may be a useful means for developing muscular strength and swimming velocity in swimmers sprints. These findings are consistent with previous reports confirming that brief periods of ES training have beneficial effects on muscle strength (2,27,32,41) and specific abilities of highly skilled athletes (28,31,40).

It is generally accepted that neural adaptations predominate in short-term strength training (42) and ES training (7,14,32). For instance, Maffiuletti et al. (28) recently suggested that ES training would increase the neural drive from supraspinal centers, resulting in a greater number of recruited motor units. Therefore, strength gains observed after the present ES training during concentric test (60 and 180°·s−1) but more likely during eccentric (−60°·s−1) maximal voluntary isokinetic contractions could be partly attributed to neural adaptations.

Nevertheless, such a conclusion is only valid for a given angular velocity, and strength gains obtained for ES group would be primarily attributed to neural adaptations preferentially affecting fast-twitch fibers. Indeed, fast-twitch fibers have been suggested to be preferentially recruited during eccentric contractions ([16,39]; for a opposite view, see [47]) and increasingly recruited at high concentric velocities (9,13,17). Moreover, the effectiveness of supplementing training with electrical stimulation is based on the concept that fast-twitch fibers are activated first and to a greater extent than that predicted by Henneman's size principle (i.e., voluntary motor unit recruitment follows a progressive recruitment of small, typically slow, motor units followed in the order of increasing size to the larger, typically fast, motor units) (12,14,15,20,44). Therefore, ES can be used to activate fast motor units in addition to slow ones (i.e., “disorderly” recruitment), even at relatively low force levels (20,26).

In conclusion, the majority of evidence suggests that ES-induced motor unit recruitment is nonselective and that muscle fibers are recruited without obvious sequencing related to fiber types (20). This unique feature has important implications for the use of ES in the context of rehabilitation and sport training (26).

Nardone et al. (38) indicated that fast-twitch fibers are preferentially recruited during submaximal exercise in the eccentric condition. Moreover, Enoka (14) and Delitto et al. (11) stated that fast-twitch fibers could be preferentially recruited during electrostimulation. This statement was confirmed by the study performed by Andersen et al. (1) and Maffiuletti et al. (29), who observed a significant change in the relative content of myosin heavy chain isoforms of 22% for type 2A muscle fibers after short-term electrostimulation resistance training. These data could explain the results obtained in this study.

The peak torque gains measured in the concentric conditions for S and ES are in agreement with the results of Häkkinen et al. (21). Indeed, they indicated that a training program in concentric and isometric conditions increases concentric and isometric strength, respectively, but not the strength of other forms of contraction. In contrast, Häkkinen et al. (21) observed that an eccentric training program induced an increase in physical strength at each contraction regimen. Indeed, the swimmers who performed the strength training program (S) in our study were asked to generate maximal intensity during the concentric phase of the movement and to maintain their effort during the isometric and eccentric phases for 3 seconds, which was certainly too short to obtain significant adaptation to these forms of contraction. In addition, the ability of electrical stimulation to enhance eccentric strength, as reported by several studies in other sports (20,27,32), by preferentially recruiting fast-twitch fibers could explain why ES peak torques increased for each condition.

The stroke length increased only in S (Table 3). This result is in agreement with those values reported by Craig et al. (10), indicating that stroke length increases were probably related to the ability to develop the force necessary for overcoming resistance to forward movement. In this study, the significant increase in physical strength in concentric conditions was correlated with the performance increase in S. Thus, this strength gain may explain the increase in stroke length. Moreover, peak torque gain was most important in the concentric condition at 180°·s−1, which is in agreement with our previous results (18) and underscores that, to be efficient, a 50-m swimmer has to generate maximal strength at high movement speed.

In this study, improvement in 50-m performance in S was correlated with improvement in concentric strength at 60 and 180°·s−1, and in ES, the same gain was correlated with the gain in eccentric strength at −60°·s−1. These data are in agreement with those of previous studies (23,24,48) showing a strong relationship between the power of the upper limbs and sprint swimming performance. Moreover, the relationship between the gain in performance and the gain in eccentric strength for ES confirms the results of Pichon et al. (40). Indeed, they reported that the variations in peak torque of the arm extensors, measured in the eccentric condition at −60°·s−1, were related to variations in performance (r = 0.77; p < 0.05) after a 3-week period of electrostimulation training. This relationship could be explained, on the one hand, by the ability of electrical stimulation to enhance eccentric strength (20,27,32), so the importance of fast-twitch fibers in strength development during eccentric contractions. On the other hand, sprint swimming performance requires both explosive force and fast-twitch fibers. The gain in performance for S was also correlated with the increase in stroke length. Several studies have demonstrated the importance of stroke length in swimming (5,8). In a 50-m sprint, stroke length is a key factor even if it is less than that observed for other swimming distances. As previously mentioned, the 50-m swimmer has to generate maximal strength at a high stroke rate to be efficient (18), and physical strength will directly influence stroke length (10).

All training effects were maintained 4 weeks after the end of the training program. These results confirm those reported by Häkkinen et al. (22), indicating that no change in strength and power occur during short periods of detraining. They also confirm the results obtained by Gondin et al. (19) concerning the preservation of maximal strength after 4 weeks of detraining subsequent to an 8-week electrical stimulation training program. Lemmer et al. (25) also reported that strength loss only occurred after 12 weeks of detraining subsequent to a 9-week strength training program.

Both the S and ES groups demonstrated significant improvements in performance as a result of their specific training. Though the improvement may stem from different signaling pathways, neither program provided such a different stimulus that the outcome was different. However, a longer period of training might lead to more variations in improvement. Further research is required to assess this question.

Practical Applications

This study shows that the methods combining swimming and dry-land S or swimming and ES were more efficient for increasing sprint performance in a 50-m front crawl than the swimming program alone. No differences in performance gain were observed between dry-land strength training and electrical stimulation training methods.

These training methods are both interesting and can be used during the entire swimming season. However, electrical stimulation misses many of the inherent characteristics of tissue stimulation related to the connective tissue and its role and compression and strain rates. In addition, little work has been done concerning connective tissues, which play an important role in kinetic chain function. However, during periods of high training volume and competition (or when the swimmer suffers from fatigue because of the accumulation of high training load or in the case of influenza, etc.), electrical stimulation may be a good replacement for dry-land strength training. The use of electrical stimulation instead of strength training during periods of high training volume and competitions may help to lower the risk of injury because of an overload of movement on the shoulder joint. Indeed, the swimmer's shoulder is the most exposed joint in water, and frequent injuries such as shoulder tendonitis are reported (34). More recently, Brushoj et al. (3) pointed out that shoulder pain is the most common musculoskeletal complaint in competitive swimmers, principally consecutive to labral pathology and subacromial impingement.

Acknowledgments

The authors wish to thank the swimmers for their voluntary participation and their enthusiasm in the training program. The authors warmly thank The club “Stade Poitevin Natation” and its board for their very inspiring atmosphere, their interest in applied research, and for making this study possible.

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Keywords:

weight training; stroke technique; muscular strength

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