Possible Hormone Predictors of Physical Performance in Adolescent Team Sport Athletes : The Journal of Strength & Conditioning Research

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Original Research

Possible Hormone Predictors of Physical Performance in Adolescent Team Sport Athletes

Martin, Alanna C.1,2; Heazlewood, Ian T.1; Kitic, Cecilia M.3; Lys, Isabelle4; Johnson, Liam5,6

Author Information
Journal of Strength and Conditioning Research 33(2):p 417-425, February 2019. | DOI: 10.1519/JSC.0000000000002014
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Abstract

Introduction

Team sports, such as Australian football (AF), basketball, field hockey, and netball, require athletes to perform game-related skills in combination with various movement patterns. These include rapid accelerations, decelerations, and changes of direction, often with jumping or leaping movements, sustaining high levels of intensity with little opportunity for sufficient recovery (19). Talented adolescents (aged 15–19 years) involved in team sports often represent school and club teams at numerous levels, as well as completing training commitments for state teams, and in some cases state institutes or academies (4). Training loads are not often coordinated across different commitments potentially exposing athletes to high physical and psychological loads (4). Selection into national squads even as a junior athlete often results in talented adolescent athletes competing year round without an off-season. Traditionally, monitoring of adolescent athletes to predict performance, injury risk, or overtraining/overreaching has involved training diaries and physical test batteries. These methods add an additional load to athletes who may already be at risk of being overloaded. Saliva analysis of specific hormones related to performance provides another possible tool for monitoring adolescent athletes.

The use of biochemical markers for both short- and long-term monitoring of exercise stress is widespread in adults. Testosterone and cortisol levels and the testosterone to cortisol ratio (T:C ratio) have been identified as markers of training stress (20). A decrease in testosterone levels and an increase in cortisol levels, or a reduction in the T:C ratio, are thought to indicate an increase in catabolic activity, representative of a state of overstrain or insufficient recovery (20). Increases in performance, however, have been identified in professional soccer players during high-intensity training despite a significant decrease in salivary T:C of over 30% (10). The authors suggested that a decrease in T:C ratio may not necessarily lead to a decrease in performance or a state of overtraining, but instead may reflect an optimal state (10). During adolescence, steroid hormone secretion is increased to meet the developmental demands of the body (Kerrigan and Rogol, 1992). Increased demands on the hormones during adolescence may result in different relationships between changes in hormone levels and changes in performance in adolescents than in adults. In adolescent soccer athletes, changes in testosterone levels have positively correlated with changes in countermovement jump (CMJ) height (r = 0.48), drop jump height (r = 0.40), and relative V̇o2max: (r = 0.32) and negatively correlated with changes in 30-m sprint speed (=0.34) (16). These results suggest that testosterone levels may influence performance in adolescent athletes, but more research is needed to confirm this result and to identify whether other hormones also influence performance.

In addition to their use as biomarkers in the monitoring of exercise stress, steroid hormones have been identified as predictors of motor performance. Testosterone has been identified as a predictor of CMJ performance (33%) and yo-yo intermittent recovery test (yo-yo) performance (21%) in adolescent male soccer athletes (13). Testosterone was also identified as a predictor of CMJ performance (16%) in adolescent male AF athletes, however, had no relationship with multistage fitness test (MSFT), speed, or agility performance (14). In the adolescent male AF athletes, progesterone and estradiol were both identified as predictors of speed and agility, though predictive power was greatest when both hormones were factored into the analysis (10 m speed: 19.1%, 20 m speed: 20.2% and agility: 30.9%) (14). The above studies suggest that pre-exercise hormone levels may be related to motor performance in adolescent team sport athletes; however, more information is needed in this area particularly on female participants.

This study had 2 main aims: first to establish whether a predicitive relationship exists between salivary hormone (testosterone, cortisol, estradiol, and progesterone) levels and physical performance in state-level adolescent team sport athletes, and second, to assess whether individual changes in hormone levels provided stronger predictive markers of changes in physical capacity than baseline values alone. Three hypotheses were developed: (a) progesterone level would be a predictor of speed, and progesterone, estradiol, and the progesterone to estradiol ratio (P:E ratio) would be a predictor of agility, (b) testosterone levels and the T:C ratio would be predictors of endurance and power, (c) stronger hormone predictors of performance would be evident when individual changes in hormone levels and motor performance were analyzed than when predictors were calculated for the pooled data.

Methods

Experimental Approach to the Problem

The aim of this prospective cohort design was to establish hormonal predictors of physical performance in state-level adolescent team sport athletes. We used athletes who were undergoing their routine testing by the Tasmanian Institute of Sport (TIS).

Between April 2013 and February 2015, team sport athletes were evaluated at their prescheduled physical testing sessions. Information on the frequency of testing and the tests completed by each sporting group is listed in Table 1. The physical performance tests were selected and conducted according to the national protocols for each sport (19) and were administered by the TIS physiologists assigned to that sport by the TIS. Although not included in the national protocol, netball athletes also completed a repeat agility test and AF athletes completed an isometric handgrip test for strength.

T1
Table 1.:
Performance testing frequency, time, and tests performed by sport.*

Participants arrived at the testing venue at approximately 10 am On arrival at the testing venue participants completed anthropometry testing then provided a saliva sample. Participants completed a warm-up of approximately 15 minutes consisting of low-intensity running followed by a series of dynamic warm-up exercises including lunge walks, butt-kicks, and leg swings and then short accelerations. Participants then completed the physical tests in the order listed in Table 1.

Before actual testing, participants were thoroughly familiarized with all testing equipment and procedures. For all testing days, participants were asked to refrain from exhaustive physical activity for 48 hours preceding testing.

Subjects

One hundred and fourteen (n = 114) adolescent athletes were recruited to participate in this study (mean ± SD; male n = 77, age 16.87 ± 1.2 years, height 184.5 ± 6.6 cm, body mass 77.1 ± 6.5 kg; female n = 37, age 16.4 ± 1.1 years, height 175.0 ± 5.9 cm, body mass 68.9 ± 9.8 kg). All participants were members of the TIS or their state sporting organization representative squads for either AF, basketball, hockey, or netball. Participants were included if they were uninjured and free from any medical conditions. Details of hormonal contraceptive use, including the type and brand of contraceptive, were obtained with the participant's permission from the TIS athlete database. The study was approved by the Charles Darwin University Human Research Ethics Committee (Approval Number: H12155). The subjects were informed of the benefits and risks of the investigation before signing an institutionally approved informed consent document to participate in the study. Parental or guardian signed consent was also obtained when participants were under the age of 18 years.

Procedures

Anthropometry

Body mass and height were measured with standard techniques to the nearest 0.1 cm and 0.1 kg, respectively, for each participant. To estimate adiposity, skinfold thicknesses were measured at 7 sites on the right side of the body (triceps, biceps, subscapular, supraspinale, abdominal, calf, and thigh) using a Harpenden skinfold caliper (British Indicators Ltd., Luton, United Kingdom). The same International Society for the Advancement of Kinanthropometry (ISAK)-accredited investigator took all measurements at each test occasion.

Countermovement Jump

The CMJ height was used as a test of explosive leg power and was determined with Yardstick jumping device (Swift, Brisbane, Australia). Participants were required to stand with their feet together side on to the Yardstick. Keeping their heels on the floor and looking straight ahead, they were required to reach upward with their dominant hand as high as possible, fully elevating the shoulder to displace the Yardstick vanes. This value was recorded as the reach height. The participant then performed a CMJ with no preliminary steps (except for the basketball athletes who as per the national protocol were permitted one preliminary step) or shuffling with the aim of displacing the highest vane possible. At least 3 trials were performed with the participant continuing to jump when they felt they were ready until missing 3 consecutive times. The highest vane displaced was recorded as the jump height. The CMJ height was then calculated as the difference between reach height and jump height (cm). Tasmanian Institute of Sport reliability scores are high for this test where intraclass correlation coefficient (ICC) is r = 0.89.

Sprints

The participants were instructed to run as fast as possible in a straight line through electronic light gates (Fusion Sports, Australia, serial number 70019522) spaced at 10, 30, and 40 m on a synthetic turf for field hockey athletes and spaced at 5, 10, and 20 m on an indoor wooden basketball court for AF, basketball, and netball athletes. Participants were instructed to start from a stationary position with their front foot touching the edge of the start line and to ensure that their first movement was in the forward direction (i.e., no rocking). Participants were able to start in their own time once they were informed that the timing system was ready and were instructed not to slow down until they were 5 m past the final timing gate. Sprint times began when the participant passed the laser positioned across the start line and concluded when they passed the laser positioned across the final marker. The fastest 5-, 10-, and 20-m time for the AF basketball and netball athletes and the fastest 10- and 40-m time for the hockey athletes were used for analysis. Tasmanian Institute of Sport reliability scores are high for this test where ICC is r = 0.97.

Multistage Fitness Test

The MSFT was used as a measure of aerobic endurance in the AF and hockey athletes. Participants were required to run back and forth on a measured 20-m synthetic turf hockey field track keeping in time with a series of audio signals from an mp3 provided by the Australian Institute of Sport and validated against the MSFT compact disc (Australian Coaching Council, Belconnen, ACT, 1998). Each end on the 20-m track was marked with cones. A test administrator was positioned at each line to ensure that the athlete placed a foot on or over the line before the audio signal and to ensure that the participant did not attempt the next shuttle until the audio signal had sounded. Participants received a warning the first time they failed to reach the line before the audio signal and were eliminated the second consecutive time. The total distance covered in meters that was reached in time with the audio signal was recorded as their final score. Tasmanian Institute of Sport reliability scores are high for this test where ICC is r = 0.97.

Yo-Yo Intermittent Recovery Test (Yo-Yo)

The yo-yo test was used as a measure of aerobic endurance in the basketball and netball athletes. Participants were required to run 40 m on an out and back course (20 m each way turning around at a line marked by cones) in time with an audio recording. On reaching the start point, the participants were to walk around a set of cones 5 m away before returning to the start line to await the next audio cue indicating to begin the next shuttle. The time between the audio cues gradually decreased. Participants received a warning the first time they failed to reach the start line before the audio signal and were eliminated the second time. The total distance covered in meters was recorded as their final score. Tasmanian Institute of Sport reliability scores for this test are r = 0.75.

Sit and Reach

The sit and reach test was used as a measure of combined hamstring and spinal flexibility in the basketball athletes. Participants were required to sit on the floor with their legs extended out in front of them placing their bare feet against the edge of the sit and reach box (Flextester, Novel Products, IL USA). Keeping one hand directly on top of each other the participant was then required to slide their hands along the top of the sit and reach box and hold the end-stretch for 2 seconds while maintaining straight legs. The distance of the fingers past the toes as marked on the sit and reach box was recorded to the nearest 0.5 cm. Tasmanian Institute of Sport reliability scores are high for this test where ICC is r = 0.98.

Basketball Agility (Agility Left and Right)

A schematic diagram of the agility test is presented in Figure 1. The agility test involved maximal effort trials of a predetermined course consisting of four 30 cm × 30 cm taped “pivot boxes” and was timed using electronic timing lights (Fusion sports, Australia). Basketball athletes completed 3 maximal trials beginning first with the front left box and then 3 trials beginning with the front right box with at least 30 seconds recovery between trials. The fastest of the 3 trials for each direction was recorded. Tasmanian Institute of Sport reliability scores are high for this test where ICC is r = 0.85.

F1
Figure 1.:
Schematic diagram of the basketball agility test.

Line Drill

The line drill was used as a test of anaerobic capacity in the basketball athletes. Participants were required to run as fast as possible to the closest free throw line (5.8 m), back to the base line (5.8 m), to the center line (14 m), back to the base line (14 m), to the distant free throw line (22.2 m), back to the base line (22.2 m), to the opposite base line (28 m), and finally to the base line where the test commenced (28 m). Electronic light gates (Fusion sports, Australia) positioned on the base line recorded the start and finish time (seconds). Each participant completed one trial, with the time taken to complete the trial recorded as the final score. Tasmanian Institute of Sport reliability scores for this test are r = 0.78.

Planned Agility

The planned agility test was completed by the netball and AF athletes. It involved maximal effort trials around a predetermined course with poles comprising 3 left and 2 right 90° turns and was timed using electronic timing lights (Fusion sports, Australia) placed at the start and finish lines. Athletes completed 3 maximal trials with at least 2 minutes recovery between trials. The fastest of the 3 trials was recorded. Figure 2 is a schematic of the planned agility test. Tasmanian Institute of Sport reliability scores are high for this test where ICC is r = 0.94.

F2
Figure 2.:
Schematic diagram of the planned agility test.

Repeat Agility Test

The repeat agility test (4 × planned agility circuit on a 20-second cycle), which measures anaerobic capacity, was also completed by the netball participants. The total time in seconds of the 4 agility trials was used as the repeat agility score.

Handgrip Strength

The handgrip strength of the AF athletes was measured bilaterally using a handheld dynamometer (Original Smedley Dynamometer 100 kg; TTM, Tokyo, Japan). The participants performed 3 maximal effort contractions with a rest period of 15–20 s between each effort. The maximum value from the 3 trials was recorded (ICC r = 0.98) (11).

Saliva Analysis

The participants were instructed to refrain from eating, drinking fluids other than water, or brushing their teeth for one hour before saliva collection to avoid sample contamination. Approximately 2 ml of saliva was collected by the passive drool method in sterile containers immediately before the participants' warm-up. All samples were coded and kept at −80° C until analysis. After thawing, the samples were centrifuged at 4,000 rpm for 5 minutes. The samples were then analyzed in duplicate for testosterone, cortisol, progesterone, and estradiol by commercially available kits as per manufacturer's instructions (Salimetrics LLC, State College, Pennsylvania, USA). The minimum detection limit was 1.0 pg·ml−1 for testosterone (mean 4.6% coefficient of variation [CV]), 0.003 μg/dl for cortisol (5.2% CV), 0.1 pg·ml−1 for estradiol (5.2% CV), and 5 pg·ml−1 for progesterone (6.1% CV).

Statistical Analyses

All variables were tested for normality using the Shapiro-Wilk test before analysis. Nonnormally distributed data were log transformed before analysis to create a normal distribution when possible. Because of well-known sex differences in human physiology (see (3) for a comprehensive review), data for males and females were analyzed separately. During analysis, the female participants' results were grouped according to whether the subject was taking hormonal contraceptives at the time of testing (NOC = not taking oral contraceptives, OC = taking oral contraceptives), as the exogenous hormones found in oral contraceptives are able to bind to other steroid receptors and either inhibit the receptor activation or induce transactivation (18). Associations between baseline and relative changes in hormone levels (change [Δ] in absolute values from session 1 to each subsequent test session) and physical performance were determined using Pearson's correlation for normal data and Spearman's correlation for nonnormal data. Correlations were considered very strong if r = 0.90 to 1.0 or −0.90 to 1.0, strong if r = 0.7 to 0.9 or −0.7 to −0.9, moderate if r = 0.5 to 0.7 or −0.5 to −0.7, and weak if r = 0.3 to 0.5 or −0.3 to −0.5 (17). Statistical analysis was performed using SPSS software (version 16; SPSS Inc., Chicago, IL, USA), with significance set at p ≤ 0.05.

Results

Over 22 months, 161 samples (male, n = 90; female NOC, n = 39; female OC, n = 32) were collected. Mean saliva hormone values and physical test results for the male and female participants (including NOC and OC groups) are presented in Table 2. In males, agility (n = 56) was weakly correlated with estradiol levels (r = 0.47, p = <0.001), P:E (r = −0.43, p = 0.001), and T:E ratios (r = −0.35, p = 0.01). Weak correlations were evident between 10-m (n = 78) and 20-m speed (n = 64) and the P:E (10 m r = −0.36, p = 0.002; 20 m r = −0.34, p = 0.002) and T:P ratios (10 m r = 0.33, p = 0.003; 20 m r = 0.37, p = 0.001). Handgrip strength (n = 34) was weakly correlated with estradiol levels (r = −0.48, p = 0.04) and the T:E ratio (r = 0.35, p = 0.04), and running left vertical jump height (n = 56) was weakly correlated with the T:E ratio (r = −0.35, p = 0.01). In the NOC group, distance covered in the MSFT was strongly correlated with the T:E ratio (r = −0.76, p = 0.01) and moderately correlated with the T:P ratio (r = −0.68, p = 0.02). In the NOC group, 1-step CMJ height (n = 10) was correlated with estradiol (r = 0.81, p = 0.01), agility left (n = 10) was correlated with estradiol (r = −0.71, p = 0.01) and the T:E (r = −0.82, p = 0.01) and T:P ratios (r = 0.71, p = 0.03), and the line drill performance (n = 10) was correlated with estradiol (r = −0.86, p = 0.001), progesterone (r = −0.79, p = 0.01), and the T:P (r = 0.70, p = 0.04) and T:E ratios (r = 0.78, p = 0.01). In the OC group, repeat agility total time (n = 20) was strongly correlated with estradiol levels (r = −0.71, p = 0.001) and moderately correlated with progesterone levels (r = −0.51, p = 0.01) and the T:E ratio (r = 0.63, p = 0.004).

T2
Table 2.:
Hormone levels and ratios by test group (mean ± SD).*

Mean individual changes in saliva values and physical test results over time for the male and female participants (including NOC and OC groups) are displayed in Table 3. Correlations between individual changes in physical performance and individual changes in salivary hormone parameters are presented in Table 4. In males, strong correlations were evident between a Δ in planned agility time and a Δ in estradiol levels (p = 0.02), and a Δ in CMJ height and a Δ in the T:C ratio (p = 0.01). In the NOC group, a strong correlation was evident between a Δ in CMJ height and a Δ in the T:P ratio (p = 0.02), and a moderate correlation was evident between a Δ in CMJ height and a Δ in the T:E ratio (p = 0.03). A moderate correlation was also evident between a Δ in 10-m speed and a ∆ in testosterone levels (p = 0.003). In the OC group, a Δ in the distance covered in the yo-yo test was strongly related to a Δ in the T:E ratio (p = 0.01) and moderately related to a ∆ in estradiol levels (p = 0.02) and the P:E ratio (p = 0.05). A strong correlation was evident between a Δ in 20-m speed and a Δ in the T:P ratio (p = 0.01), and moderate correlations were evident between a Δ in 20-m speed and a Δ in the T:C ratio (p = 0.03), and a Δ in 5-m speed and a Δ in the T:P ratio (p = 0.04).

T3
Table 3.:
Individual change in hormone levels and physical test performance by test group (mean ± SD).*
T4
Table 4.:
Correlations between individual changes in physical performance and individual changes in salivary hormone parameters.*

Discussion

The aim of this study was to determine possible hormone predictors of physical performance in adolescent team sport athletes and to assess whether individual changes in hormone levels provided stronger predictive markers of changes in physical capacity than discrete values. Our results identified some significant hormonal predictors of physical performance. Individual changes in estradiol levels were a stronger predictor of planned agility performance than pooled estradiol levels in the male athletes.

Published research on adolescent AF athletes identified estradiol and progesterone as predictors of 10- and 20-m sprint speed (14). Given this, we hypothesized that salivary progesterone levels would be positively associated with speed and power test performance in our sample of adolescent athletes. This is the first study of its kind to identify a positive association between the P:E ratio and speed and agility performance, and a negative association between the T:P ratio and speed in males. It is proposed that this finding may be due to progesterone's antagonistic effects of estradiol at a receptor level. Progesterone functions as an inhibitor of estrogen (21) and estrogen receptors (12). Progesterone represses estrogen receptor transcriptional activity, antagonizes estrogen action at the molecular level, and prevents estrogen induction by downregulating estrogen protein concentration (12). Progesterone has also been found to affect estrogen-stimulated responses, though the mechanisms in which this occurs are unclear (5–7). In the female OC and NOC groups, progesterone levels were not associated with speed and agility; however, moderate to strong negative associations between changes in speed and salivary testosterone levels, T:C, and T:P ratios were identified in both groups. To the best of our knowledge, no study has directly investigated possible associations between speed or agility and testosterone levels in females, though a study on male Rugby Union athletes did identify a positive relationship between both salivary testosterone levels and T:C ratio and speed (8). This result in male Rugby Union athletes contrasts with our finding in female team sport athletes. Recent research suggests that testosterones responses during exercise may be mediated by cortisol levels; however, the mechanisms are yet to be elucidated (9). The finding that cortisol levels may mediate testosterone responses complement findings in behavioral studies. Behavioral studies have reported testosterone relationships that are mostly positive when cortisol levels are low and negative when cortisol levels are high (15). Female participants in this study had notably higher cortisol levels (NOC = 12.8 ± 7.6 nmol·L−1, OC = 11.2 ± 4.6 nmol·L−1) than the male Rugby Union athletes (Backs = 5.1 ± 2.4 nmol/L, Forwards = 7.3 ± 3.5 nmol·L−1) in the study by Crewther, Lowe, Weatherby, Gill, and Keogh (8) which may explain why the T:C ratio in our study had a negative relationship with speed, whereas the relationship was positive in the male Rugby Union athletes.

In contrast to previous findings in male adolescent athletes (1), individual changes in the T:C ratio were negatively associated with individual changes in CMJ height in male participants. A decrease in the bioavailable T:C ratio has been previously linked to overtraining (20); however, increases in performance have been identified in professional soccer players during high-intensity training despite a significant decrease in salivary T:C of over 30% (10). It has been suggested that a decrease in T:C ratio may not necessarily lead to a decrease in performance or a state of overtraining, but instead may reflect an optimal performance state (10). Rather than a measure of overtraining, the T:C ratio may be indicative of training stress (20). Training stress is necessary to induce positive changes in response to training; however, the optimal level of stress required, and how it is reflected in the T:C ratio, remains unknown.

This study is not without limitations. Interpretation of our results is limited by the small sample size for some of the physical performance tests. The results of this study are restricted to the population of athletes tested and may not be indicative of the general population or other athlete groups. For research outcomes to be adopted and used effectively within sports, they must be proven to be feasible and effective in real-world settings (2). As a consequence of this concept, the researchers were interested in identifying hormone predictors of performance that were independent of other factors such as training phase, diet, clothing, and sleep patterns. As a result, training phase, diet, clothing, and sleep patterns were not reported or considered in the analysis of this study.

In conclusion, the current results showed that in adolescent team sport athletes, the P:E, T:E, and the T:P ratios are important predictors of motor performance in tests of physical capacity. The current findings also allow us to indicate that estradiol and progesterone have a role in the physical performance of adolescent male team sport athletes. Contrary to the initial hypothesis, in most cases, analysis of individual changes in hormone levels did not act as stronger predictors of performance than discrete values.

Practical Applications

This study provides insights into possible hormone predictors of performance in adolescent team sport athletes. Coaches and support staff should keep in mind when using hormone levels to predict athlete performance that monitoring changes in hormone levels and performance, and looking at discrete variables of hormones and performance do not yield identical results. In adolescent female team sport athletes, the preferred method of monitoring should be individual changes in hormone levels (testosterone, P:E, T:P, and T:E ratios) and performance. It is also important to note whether female athletes are taking hormonal contraceptives at the time of testing, as the exogenous hormone contained in hormonal contraceptives may affect the results. In adolescent male team sport athletes, the method of prediction should depend on the variable being predicted. The results of this study indicate that changes in estradiol levels may provide a useful biomarker of agility and support the use of the T:C ratio as a marker of training stress in adolescent male team sport athletes. In addition, discrete measurements of the P:E ratio may be useful in predicting speed and agility in adolescent male team sport athletes. This has possible implications as an initial screening tool for talent identification models applied in different sports.

Acknowledgments

This project was funded by Charles Darwin University under a 2012 project grant. The authors thank the Tasmanian Institute of Sport and the University of Tasmania for their contribution. They also thank the participants, coaches, physiologists, AFL Tasmania, and Netball Tasmania for their assistance with this study. The results of this study do not constitute endorsement of the product by the authors or the NSCA.

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Keywords:

testosterone; estradiol; progesterone; cortisol; exercise

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