International Journal of Sports Physiology and Performance, 2016, 11, 33  -39 http://dx.doi.org/10.1123/ijspp.2014-0310 © 2016 Human Kinetics, Inc.

ORIGINAL INVESTIGATION

Relationship Between Fatigue and Changes in Swim Technique During an Exhaustive Swim Exercise Natália M. Bassan, Tadeu E.A.S. César, Benedito S. Denadai, and Camila C. Greco Purpose: To analyze the relationship between the responses of isometric peak torque (IPT) and maximal rate of force development (RFDmax) with the changes in stroking parameters in an exhaustive exercise performed in front crawl. Methods: Fifteen male swimmers performed, on different days, the following protocols: maximal 400-m trial, strength tests before and after an exhaustive test at 100% of the mean speed obtained during the 400-m test, and the same procedures on day 2. Results: The IPT of elbow flexors (79.9 ± 19.4 and 66.7 ± 20.0 N·m) and elbow extensors (95.1 ± 28.0 N·m and 85.8 ± 30.5 N·m) was decreased after the swim test, as was RFDmax (521.8 ± 198.6 and 426.0 ± 229.9 N·m/s; 420.6 ± 168.2 and 384.0 ± 143.5 N·m/s, respectively). Stroke length decreased during the swim test (1.96 ± 0.22 and 1.68 ± 0.29 m/stroke), while stroke rate increased (37.2 ± 3.14 and 41.3 ± 4.32 strokes/min). The propulsive phases increased while the nonpropulsive phases decreased during the test. Significant correlation was found between the changes in IPT and stroke length, stroke rate and recovery (elbow flexors), and entry and catch phase (elbow extensors). In addition, significant correlation was found between the changes in RFDmax of elbow flexors with the changes in pull and recovery phases. Conclusion: Changes in swim technique during an exhaustive test can be, at least in part, associated with fatigue of the arm muscles. Keywords: neuromuscular, swimming, front crawl, evaluation and training. In swimming, high levels of power output and propelling efficiency, as well as reduced drag, are important to develop high swim speeds.1 In front-crawl swimming, 85% of the propulsion is produced mainly by arm movements.2 Specifically, the triceps brachii and the biceps brachii muscles are important for propulsion during the underwater phase of the stroke.3 To develop a given speed, the swimmers may adopt different combinations of stroke rate (SR) and stroke length (SL), with the latter being considered one of the best indexes for swimming-performance prediction.4 In addition to expressing propulsive efficiency,5 SL has been shown to be decreased during fatigue.6 During competitive races7 or tests that simulate a swim event,6,8,9 there is a gradual decrease in SL and SR, which results in reduced swim speed. However, during exhaustive constant-speed tests,10 there is a gradual decrease in SL and an increase in SR in an attempt to maintain the speed. Alberty et al10 observed that in absolute values, the duration of the nonpropulsive phases decreased and the propulsive phases were maintained during tests performed at 95%, 100%, and 110% of 400-m performance (V400). In addition, there was a significant increase of index of coordination (IdC), indicating a reduced gap between propulsive actions. The increased SR and IdC during these conditions allows longer duration over which the propulsive force is applied to maintain the swimmer’s speed.10 In both self-selected and constant-speed conditions, fatigue (ie, an exercise-induced decline in the capability of the muscle to generate force or power)11 seems to be an essential aspect to explain the swim-technique adjustments, particularly the reduction of SL. The authors are with the Human Performance Laboratory, São Paulo State University, São Paulo, Brazil. Address author correspondence to Camila Greco at [email protected].

Thus, the compromised capacity to generate force to overcome drag has been suggested to contribute to the decrease in SR and SL.7 Indeed, using a swim bench, Aujouannet et al8 showed reduced values of maximal isometric force after a maximal 4 × 50-m swim test. Moreover, Ikuta et al6 and Figueiredo et al9 demonstrated significant changes in electromyography parameters during a maximal 4 × 50-m swim test and a maximal 200-m front-crawl swim test, respectively. Although researchers have identified a significant correlation between the change in electromyography activity and the variation in swim speed and angular arm velocity,6 no studies have determined the relationship between changes in muscle strength/ power (ie, fatigue) and swim technique in exhaustive swim tests. Therefore, the main objective of this study was to analyze the relationship between the responses of isometric peak torque (IPT) and maximal rate of force development (ie, explosive muscle strength) (RFDmax) with the changes on stroking parameters in an exhaustive exercise performed in front crawl. We hypothesized that an exhaustive test would lead to changes in swim technique, maximal force, and explosive force and that a direct relationship might exist between the changes in swim technique with the changes in muscle force. However, to monitor muscle fatigue and training interventions in regional-level competitive male swimmers, reliable measures of neuromuscular parameters (ie, maximal force and explosive force), technical indexes (SR and SL), and stroke phases are essential. The greater the reliability of the measure, the higher the probability that a meaningful change would be detected. Thus, the second aim of this study was to analyze the reliability of the following parameters: maximal force (IPT) and explosive force (RFDmax) of elbow flexors and elbow extensors before and after an exhaustive swim test; SR, SL, and stroke phases during the exhaustive swim test; and time to exhaustion at 100%V400 in regional-level competitive male swimmers.

33

34  Bassan et al

Methods

Downloaded by University of Exeter on 10/13/16, Volume 11, Article Number 1

Participants Fifteen regional-level competitive male swimmers (mean ± SD age = 24 ± 5 y, stature = 1.77 ± 0.06 m, body mass = 74.4 ± 0.09 kg) volunteered and gave written informed consent to participate in the current study, which was approved by the local ethics committee of São Paulo State University (Protocol 128/13). Participants were competing in several regional- and national-level meets over middle to long distances (400–1500 m) and had trained for at least 3 years, around 5 times a week. Their mean 400-m front-crawl performance (V400) at the time of the study was equal to 71.8% ± 5.0% of the mean speed of the short-course world record. The participants were instructed to refrain from intense training sessions at least 48 hours before the experimental sessions. In addition, they were instructed to be fully rested and hydrated at least 3 hours postprandially when reporting to the laboratory and to refrain from using caffeine-containing food or beverages, drugs, alcohol, cigarettes, or any form of nicotine 24 hours before testing.

Design The participants were required to visit the laboratory on 3 different occasions, separated by at least 48 hours, within a period of 2 weeks. The first testing was a familiarization session, and the 2 subsequent visits were the experimental trials. Familiarization included anthropometric assessments (body mass and height) followed by a practice of the isometric tests that would be completed during the experimental trials. In addition, participants performed a maximal 400-m trial in a 25-m swimming pool to determine V400. On the second visit, participants performed maximal isometric contractions using an isokinetic dynamometer (Biodex System 3, Biodex Medical Systems, Shirley, NY) to calculate their IPT and RFDmax. This test was performed immediately before and after (≤3 min) a constant-speed test to exhaustion at 100%V400. On the third visit, participants performed the same procedures as on the second visit. The tests were performed in a 25-m outdoor swimming pool (29°C), using front crawl from a push start. A standard warm-up was consistently performed before each test. Testing occurred at the same time of the day (± 2 h) to minimize the effect of circadian variation on performance. Determination of Muscle Strength.  Participants were placed in a sitting position, securely strapped into the test chair. Extraneous movement of the upper body was limited by 2 crossover shoulder harnesses and an abdomen belt. The trunk/thigh angle was 85°. All subjects had been familiarized with the test procedures on the isokinetic dynamometer in a separate session, to avoid strength underestimation.12 Warm-up consisted of a set of 5 submaximal isometric contractions for each muscle group (ie, elbow flexors and elbow extensors). Two maximal isometric voluntary contractions of 3 seconds, with 3 minutes rest between, were performed to determine the IPT of elbow flexors and elbow extensors. The participants were instructed to perform a maximum effort for each trial, and strong verbal encouragement was provided by the investigators. For elbow-flexor and elbow-extensor muscle contractions, a plastic molded wrist brace was worn to limit synergist activity of the forearm muscles. For elbow-flexor muscles, the forearm/wrist of the participant was strapped to a firmly padded arm attachment that was fastened to the dynamometer handle, and the participant pulled on the apparatus to perform the contraction. The arm was positioned at 30° of flexion, with 0° being full extension, and the

hand was in a supine position. The procedures used to measure elbow-extensor muscles were similar, with the hand positioned in prone. The shoulder position was 45° of external rotation and 45° of anatomic position. The tests for elbow flexors and elbow extensors were performed in a randomized order. However, the sequence of tests was the same before and after the exhaustive swim test. Data Processing.  The torque data of the contractions were

collected at a 1000-Hz frequency by a biological-signal-acquisition module (EMG System) synchronized with the isokinetic dynamometer. The data were filtered (Butterworth filter, lowpass, fourth-order, with a 15-Hz cutoff frequency) and analyzed in MATLAB 6.5 software (Mathworks, USA). The isometric peak torque was considered the highest value in the torque–time curve. RFD was obtained by the slope of the isometric contraction torque–time curve. RFDmax was calculated as the steepest point of the torque–time curve (ie, Δtorque/Δtime). The onset of muscle contraction was defined as the point where the torque–time curve exceeded 2.5% of the difference between baseline moment and peak isometric moment.13

Determination of 400-m Performance.  The participants were instructed to swim the 400-m front crawl at their maximum effort; they were not instructed to swim at a constant speed. The time taken to swim the distance was recorded using a manual chronometer. V400 was calculated as the ratio of distance (ie, 400 m) to time. Determination of Time to Exhaustion.  The constant-speed tests

were performed at 100%V400 until voluntary exhaustion or when the participant did not maintain the imposed swim speed, even with verbal and visual stimuli. During the exhaustive constant-speed test, the swimming speed was controlled using an mp3 player attached to each swimmer’s goggles (MP120B/F, Oregon Scientific). A regular audible signal enabled the swimmer to maintain the target pace. Red marks were traced every 5 m on the bottom of the pool and the swimmer was instructed to pass his feet across the marker on each “beep.” The test continued until the swimmer’s head showed behind the red mark. The difference between predicted and actual swim speed was lower than 2% in all tests. Time to exhaustion was recorded using a manual chronometer.

Swim-Technique Parameters.  The swimmers were filmed during

all tests by 2 cameras, 1 above the surface of the water (Samsung, operating at 60 Hz) and 1 below (Go Pro Hero 3, operating at 60 Hz and contained in a waterproof box). The time to complete 5 stroke cycles was recorded to calculate the SR. This procedure was performed at the beginning (between the first 25th and 50th meters) and the end (last 25 m swum at the imposed speed) of the constantspeed test. The speed was recorded using a manual chronometer, and the SL was calculated as the ratio of speed to SR. A distance of 12.5 m, between 10 and 22.5 m, was considered for the analyses. The last pool length considered was that preceding 2 consecutive laps with the speed lower than 97.5% of the imposed pace.14 Three arm strokes were analyzed at the beginning and the end of the constant-speed test. The stroke phases were quantified following the methodology proposed by Chollet et al.15 Briefly, each arm stroke was divided into 4 distinct phases, defined as entry and catch, pull, push, and recovery, expressed in seconds. The duration of a complete arm stroke was the sum of the 4 phases. The lag time between the beginning of propulsion in the first right-arm stroke and the end of propulsion in the first left-arm stroke defined IdC1 (ie, arm coordination to the left side), which was expressed as a percentage of the duration of a complete stroke. The lag time between the beginning of propulsion in the second left-arm stroke

IJSPP Vol. 11, No. 1, 2016

Fatigue and Swim Technique   35

and the end of propulsion in the first right-arm stroke defined IdC2 (ie, arm coordination to the right side), which was also expressed as a percentage of the duration of a complete stroke. IdC was thus the mean of IdC1 and IdC2.

Downloaded by University of Exeter on 10/13/16, Volume 11, Article Number 1

Statistical Analysis Data were presented as a mean ± SD. The normal distribution of all dependent variables was examined by Shapiro-Wilk test. Student t test for paired data, intraclass correlation coefficient (ICC), confidence interval (CI), and coefficient of variation (CV) were calculated according to Hopkins16 to determine test–retest reliability. CV represented the variation in a participant’s test score from measurement to measurement.16 CIs were calculated to determine the limits of agreement between trials. Reliability was classified in accordance with ICC values as poor (.75).17 A Student t test for paired samples was used to compare pretest and posttest conditions for each variable. Considering that the participants performed a familiarization session, and the IPT and RFD presented moderate to excellent test–retest reliability, the first day was used for analysis of the relationship between the responses of IPT and RFDmax with the changes in stroke parameters. The correlations between the changes in mechanical muscle function (IPT and RFDmax) and stroke parameters were performed using Spearman correlation test. The significance level was set at P ≤ .05.

Results The mean ± SD value of V400 was 1.35 ± 0.15 m/s. The times to exhaustion on the first (227.5 ± 29.2 s) and second (219.5 ± 35.1 s) days were similar (P = .22). The reliability of time to exhaustion was moderate (ICC = .73, CI95% = .24–.90, CV = 12%). The descriptive information of the reliability of the IPT and RFDmax values obtained before and after the exhaustive swim test is presented in Table 1. No significant difference was found between day 1 and day 2 for IPT and RFDmax values obtained before and after the exhaustive swim test (P > .05). The results of the ICC coefficients indicated moderate to excellent test–retest reliability on all measures for both elbow flexors and elbow extensors. The CVs for these variables ranged between 4.5% and 31.8%. The descriptive information on the reliability of SR, SL, and stroke phases—entry and catch, pull, push, and recovery—obtained during the exhaustive swim test is presented in Table 2. No significant difference was found between day 1 and day 2 for any variables (P > .05). The CV for these variables ranged between 2.4% and 11.8%. The results of the ICC coefficients indicated excellent test–retest reliability for SR and SL and poor to excellent reliability for the stroke phases. IPT and RFDmax of elbow flexors (16.1% and 18.4%, respectively) and elbow extensors (9.8% and 8.6%, respectively) were decreased after the exhaustive swim test (P < .05) (Figure 1).

Table 1  Intraclass Correlation Coefficient (ICC), 95% Confidence Interval (CI95%), and Typical Error of Measurement Expressed as a Coefficient of Variation (CV) for Isometric Peak Torque and Maximal Rate of Force Development of Elbow Flexors and Elbow Extensors, Measured Before and After the Exhaustive Swim Test, N = 15 Pretest ICC

CI95%

Posttest CV (%)

ICC

CI95%

CV (%)

Elbow flexors   isometric peak torque

.98

.95–.99

4.5

.89

.64–.96

9.8

  maximal rate of force development

.91

.74–.97

15.0

.54

–.14 to .82

31.8

  isometric peak torque

.98

.94–.99

6.1

.90

.69–.96

11.5

  maximal rate of force development

.79

.37–.93

11.7

.80

.42–.93

23.8

Elbow extensors

Table 2  Intraclass Correlation Coefficient (ICC), 95% Confidence Interval (CI95%), and Typical Error of Measurement Expressed as a Coefficient of Variation (CV) for Stroke Rate, Stroke Length, Entry and Catch, Pull, Push, and Recovery Phases at Initial and Final Parts of the Exhaustive Swim Test, N = 15 Initial

Final

ICC

CI95%

CV (%)

ICC

CI95%

CV (%)

Stroke length

.97

.89–.99

2.4

.98

.92–.99

3.6

Stroke rate

.78

.35–.92

4.9

.92

.75–.97

4.1

Entry and catch

.96

.85–.98

10.3

.96

.87–.99

11.8

Pull

.41

–.35 to .76

11.4

.95

.84–.98

8.2

Push

.92

.75–.97

4.2

.92

.74–.97

4.2

Recovery

.80

.41–.93

6.2

.73

.25–.90

5.9

IJSPP Vol. 11, No. 1, 2016

36  Bassan et al

Downloaded by University of Exeter on 10/13/16, Volume 11, Article Number 1

Figure 1 — Mean ± SD values of isometric peak torque (IPT) and maximal rate of force development (RFDmax) of elbow flexors and extensors before (Pre) and after (Post) an exhaustive swim test, N = 15 *P < .05 in relation to Pre.

SR increased (37.2 ± 3.14 vs 41.3 ± 4.32 strokes/min) and SL decreased (1.96 ± 0.22 vs 1.68 ± 0.29 m/stroke) between the beginning and final parts of the exhaustive swim test (P < .05). Stroke-phase durations, expressed as absolute values, were significantly different between the beginning and final parts of the test (P < .05). The pull (17%) and push (7%) phases increased significantly, while the entry and catch (27%) and recovery (22%) phases significantly decreased (P < .05). When expressed as relative values, the responses of the stroke phases were similar. The pull (beginning = 26.5 ± 4.1%; final = 33.3% ± 7.0%) and push (beginning = 21.1% ± 3.7%; final = 24.9% ± 4.8%) phases significantly increased, while the entry and catch (beginning = 27.2% ± 8.7%; final = 20.8% ± 11.6%) and recovery (beginning = 25.0% ± 3.68%; final = 20.1% ± 3.20%) phases significantly decreased (P < .05). IdC significantly increased (beginning = –3.17% ± 13.7%; final = 8.48% ± 15.4%; P < .05) (Figure 2). Table 3 indicates the relationships between the change in IPT of elbow flexors and elbow extensors and the changes of stroke parameters and stroke phases. There were significant correlations between the change in IPT of elbow flexors and the changes in SR and SL (P < .05). However, no significant correlation was found for RFDmax (P > .05). In addition, no significant correlations were found between the changes in IPT and RFDmax of the elbow extensors with changes in SR and SL (P > .05). Considering the changes in stroke phases, there were significant correlations between the change in IPT of the elbow flexors and the changes in recovery phase, as well as between the change in RFD of the elbow flexors and the changes in pull and recovery phases (P < .05). For the elbow-extensor muscles, there was significant correlation between the change in IPT and the change in the entry and catch phase (P < .05). No significant correlations were found for the changes in RFDmax and stroke phases (P > .05).

Discussion The main objective of this study was to analyze the relationship between the responses of neuromuscular parameters (ie, maximal force and explosive force), technical indexes, and stroke phases in an exhaustive exercise performed in front crawl. Similar to previous studies, it was demonstrated that both technical indexes10 and

Figure 2 — Mean ± SD values of the duration of the stroke phases at the beginning and the final part of the exhaustive swim test, N = 15. *P < .05 in relation to beginning.

neuromuscular parameters8 were impaired during the maximal constant-speed test. However, the main original finding of the current study was that the reductions in muscle capacity to generate force and power (ie, fatigue) were associated with the changes in SR, SL, and stroke phases (ie, entry + catch, recovery, and pull). These findings confirm and extend the notion that fatigue affects swim technique and temporal organization of the arm-stroke cycle during maximal constant-speed tests.8,10 Thus, fatigue could explain the compensatory strategy between SR and SL aiming to maintain swim speed.10 With the exception of elbow-flexor RFDmax after the exhaustive exercise (ICC = .54), the IPT and RFDmax values presented excellent reliability (ICC > .75) for both elbow flexors and elbow extensors, irrespective of condition (ie, before or after exhaustive swim exercise). However, similar to past research,18,19 the test– retest typical error was less for IPT (4.5–11.5%) than for RFDmax (11.7–31.8%). Several studies have shown that the factors influenc-

IJSPP Vol. 11, No. 1, 2016

Fatigue and Swim Technique   37

Table 3  Coefficient of Correlation (r) Between the Changes (Δ) of Isometric Peak Torque (IPT), Maximal Rate of Force Development (RFDmax), Stroke Rate (SR), Stroke Length (SL), Duration of Entry and Catch Phase, Pull Phase, Push Phase, and Recovery Phase, N = 15 ΔSR

ΔSL

Δentry and catch

Δpull

Δpush

Δrecovery

–.54*

.69*

.18

.09

.35

.52*

.32

.42

–.10

–.48*

.44

.46*

  ΔIPT

.21

–.28

.70*

.36

.13

–.02

  ΔRFDmax

–.09

.09

–.16

.11

–.25

.39

Elbow flexors   ΔIPT   ΔRFDmax Elbow extensors

Downloaded by University of Exeter on 10/13/16, Volume 11, Article Number 1

*P < .05.

ing IPT and RFDmax are not exactly the same.20–22 RFDmax is obtained at the early phase of muscle contraction (

Relationship Between Fatigue and Changes in Swim Technique During an Exhaustive Swim Exercise.

To analyze the relationship between the responses of isometric peak torque (IPT) and maximal rate of force development (RFDmax) with the changes in st...
548KB Sizes 0 Downloads 8 Views