In the United States, older adults (>65 years) represented 14.1% of the population in 2013 and are expected to reach 21.7% of the population by the year 2040, with the majority being women (1,38). Aging leads to reduced muscle mass, muscular strength, muscular power, and increased rate of fatigue, leading to functional limitations among older adults (5). As muscular strength and power decline, the ability to perform activities of daily living (ADLs) such as grocery shopping and household chores also deteriorates.
Functional performance among older adults is highly correlated with muscular strength, and recent evidence suggests that muscular power may be a greater predictor of mobility when compared with muscular strength among this group (7,19). While strength and power both decline with age, power declines at a faster rate after 50 years (27). Leg power is a strong indicator of functional ability and limitations in older adults (9,35); therefore, declines in power within older individuals is an aspect that leads to a loss of independence as well (29,31). Muscular power may be assessed by vertical jump, isokinetic dynamometry, and the Wingate anaerobic cycle test. The 30-second Wingate protocol is a valid measure of power and anaerobic capacity in women athletes (25,40). Measures of anaerobic capacity are an important factor in determining the explosiveness of an athlete. These measures translate into many aspects of sports such as change of direction and sustaining power throughout long rallies during competition indicative of sports such as tennis. Within the sport of tennis, the ability to maintain power throughout the entirety of a set is highly important. Therefore, the appropriateness of using the Wingate to assess the athlete's ability to sustain power throughout the length of the test has the potential to translate into match length and the ability to sustain power throughout competition.
Master athletes (MA) are a cohort of older adults that are continually seeking avenues with which they can participate in higher-level sport-based competitions. The number of competitive older adults participating in the United States Senior Games has increased by more than 500% since its inception in 1987 (18). As this group strives to participate at the highest level of competition, they also compete with the detrimental effects of aging. The aging process causes many physiological changes, such as loss of muscular strength and power that impairs ADLs or even loss of physical independence. Age-related physiological changes such as losses in muscular strength and power, as well as an increased rate of fatigue causes levels of physical activity and exercise performance to decline (32). As performance measures deteriorate, certain aspects such as strength and power become more difficult to maintain even with regular exercise training being performed (22,34,37). With MA becoming an ever-growing group of exercisers, it is important to compare performance measures of MA with younger individuals to determine whether continued competitive is an effective mechanism to thwart age-related decrements in physical performance. Tennis is one of the most popular sports worldwide, and requires various physical performance attributes for success (23). Grip strength is important for maximal power when contacting the ball with the racket, during both the serve and volley of any match (10,16). Explosive power, like that measured during the vertical jump, isokinetic measures, and anaerobic cycling, is also very important when observing the attributes of tennis as these power measures are used throughout a given match (33). Anaerobic capacity is also an important factor when taking into account the possibility of long rallies that occur throughout a tennis match; having the ability to sustain performance throughout these situations allows for optimal opportunities for success (24). Therefore, the purpose of this study was to determine whether MA tennis players have the ability produce similar performance measures as younger recreationally active (RA) women.
Experimental Approach to the Problem
The current cross-sectional investigation aimed to compare the performance outcomes of young, RA, and master athlete female tennis players. Participants reported to the human performance laboratory on the university campus on 2 separate days for all trials. A balance beam scale and stadiometer (Detecto, Webb City, MO, USA) were used to assess body mass and height, respectively. Body fat and lean mass were measured by dual-energy x-ray absorptiometry (DXA; General Electric, Fairfield, CT, USA). For the DXA, proper calibration procedures and quality assurance analysis were followed as previously described (10). The second day's visit involved performance measures consisting of grip strength, vertical jump, isokinetic strength measures, and anaerobic cycling performance, in that respective order. A 10-minute active recovery on an exercise bike was used after the isokinetic testing. After the active recovery the participant was then placed on the Wingate for a 5-minute warm-up before beginning the anaerobic testing. Depending on the competition or organization, age cutoffs for masters competition can vary from 30 (39) to 50 years (20,28) and for the purposes of this investigation, the average (40 years) was used as the minimum age cutoff for the MA.
This study included 15 RA (Mean ± SD 20.6 ± 0.8 years) and 17 MA (Mean ± SD 50.5 ± 8.6 years) (age range: 19–22 years and 40–68 years) women from the Southern region of the United States (Table 1). Previous investigations using women (11) determined that for significant differences to be found between 2 dependent mean values, with a power of 0.8 and alpha level of 0.05, a minimum a priori sample of 15 participants would be required per group (G*Power version 184.108.40.206; Universität Düsseldorf, Kiel, Germany). The inclusion criteria consisted of the following: categorized as low-risk by the American College of Sports Medicine (2), and playing tennis at least 2 times per week over a minimum 2-year period; with RA playing 4.2 ± 1.7 days per week and MA: 3.4 ± 0.9 days per week, whereas RA and MA had 7.3 ± 4.6 and 10 ± 8.2 years of training experience, respectively (Table 2). All participants also refrained from vigorous exercise, alcohol, and caffeine 24 hours before the trial. The initial visit included the signing of an approved informed consent, completion of a health history questionnaire, demographic assessments, body composition measurements, and familiarization of the exercise protocols. The University of Arkansas' review board approved all measures and procedures before testing.
Isometric grip strength was assessed by trained technicians and measured in kilograms (kg) using a handheld dynamometer (Takei Scientific Instrument Co., Niigata City, Japan). All grip strength measurements were performed on the preferred hand with the subject standing, arm hanging at the side, wrist in a neutral position, and the middle joint of the index finger maintained at 90°. Participants maximally squeezed the dynamometer for 5 seconds while standard encouragement was provided. Participants completed 3 separate trials with a 60-second rest between (13). Maximum grip strength (GripMAX) was determined using the highest measurement of the 3 repetitions. High test-retest reliability (ICC = 0.95) for the HG strength test has been previously recorded (6).
Maximal vertical jump height was measured using the Vertec Jump Trainer (Sports Imports, Columbus, OH, USA). Participants performed as many trials as necessary to reach maximal vertical jump height, defined as 2 unsuccessful attempts. Subjects started by standing directly beneath the Vertec and reaching up as high as possible with the preferred hand to establish a “zero” height where the jump assessment would begin. When ready, the subject performed a counter-movement jump and pushed their hand through the highest achievable vane (15). Once maximal vertical jump height was determined, it was used to calculate peak (PVP) and average vertical power (AVP) based on the following previously validated equations by Johnson and Bahamonde (21) (equations 1 and 2):
The Biodex system II Isokinetic Dynamometer (Biodex Medical, Inc., Shirley, NY, USA) measured isokinetic (ISO) strength and endurance of the knee flexors and extensors. The subject was seated on the dynamometer with the back flat against the chair and stabilized using thigh, pelvic, and shoulder straps. The chair and dynamometer settings were recorded to ensure similar positioning for all testing trials. The mechanical axis of the dynamometer was aligned with the lateral femoral condyle of the preferred leg. Before testing, all subjects received instructions to extend and flex the knee joint through full range of motion during each repetition. Subjects fully extended and flexed the knee maximally during 2 separate testing protocols. The first involved 5 repetitions (muscular strength) with flexion/extension movement parameters set at 60°·s−1. The second involved 50 repetitions (muscular endurance) with flexion/extension movement parameters set at 180°·s−1. Subjects had a 5-minute rest period between the 2 protocols (14). Variables assessed during these protocols included peak torque (PkTq), peak torque body weight (PkTqBW), total work (TotWK), and fatigue index (FI). To ensure that maximal effort was given during the evaluation, standardized verbal encouragement was provided throughout each testing session in a consistent inflection and volume level for all participants (3). Biodex system II Isokinetic Dynamometer validity (8) and reliability (ICC = 0.95–0.97) (17) have been previously demonstrated.
Anaerobic Cycling Performance
Peak power (PPWR), average power (APWR), and fatigue rates (FI) were evaluated during a traditional 30-second Wingate cycling test as previously used by Glenn et al. and others (4,12,30). During this protocol, the subject was given a 5-minute warm-up period in which they pedaled at a self-selected cadence (RPM) at a resistance of 50 watts (W). The subject was instructed to increase their cadence during the final 20 seconds of the warm-up and was given a countdown during the final 5 seconds for the subject to increase their cadence to maximal levels. At this point, the subject began the Wingate protocol and pedaled as fast as possible with maximal effort for 30 seconds at 7.5% of their bodyweight (4). Peak power (W) was determined to be the highest amount of power produced by the participant during the Wingate protocol. Average power (W) was assessed by totaling the amount of power produced by the individual during the entire protocol and then dividing that value by the total trial time (30 seconds).
SPSS version 23 (IBM, Amrok, NY, USA) was used to analyze all data. Independent sample t-tests were used to assess the differences between the RA and MA. An alpha level of p ≤ 0.05 defined statistical significance.
Independent variables included the groups assessed (RA vs. MA). Dependent variables included grip strength, vertical power, isokinetic measures, and anaerobic cycling performance. Maximum measurements were analyzed for grip strength, whereas maximum and average measures were analyzed for vertical power. Isokinetic measures included extension and flexion for a 5-repetition strength protocol, and a 50-repetition endurance-based protocol. Anaerobic cycling performance analyzed PPWR and APWR, total work (WRK) completed, as well as FI.
There were no significant differences observed for demographic information (height, weight, and body fat percentage), outside age (p ≤ 0.01), between the 2 groups (Table 1). There were no significant differences observed for years training and hours playing per week (p > 0.05); however, there was significance found for times playing per week (p ≤ 0.01) between the 2 groups (Table 2).
Strength and Power Measures
There were no significant differences observed between the RA and MA groups for GripMAX measures (Table 3, p > 0.05). There was a significant difference observed between groups for PVP and AVP (Table 3, p ≤ 0.05) measures with 9.2 and 16.4% differences in PVP and AVP, respectively, in favor of the RA group.
There were no significant differences observed between groups for any measures assessed during the Wingate anaerobic power test (Table 4, p > 0.05). However, there was a trend for APWR and WRK during the Wingate test for both measures (p = 0.09).
For PkTq, peak torque to body weight (PkTqBW, and TotWK, there was a 23.9, 27.2, and 20.9% difference, respectively, in favor of the RA for ISO 5 REP extension measures and during the ISO 5 REP flexion measures at a 14.9, 18.9, and 19.1% difference for PkTq, PkTqBW, and TotWK, respectively (Table 5, p > 0.05).
When observing the differences between groups for ISO 50 REP extension measures, there was a 17.6, 27.9, 16.9, and 4.4% difference in favor of RA for PkTq, PkTqBW, TotWK, and FI, respectively. When observing the ISO 50 REP flexion measures, there was a 22.4 and 6.5% difference for TotWK and FI in favor of the RA, respectively (Table 6, p > 0.05).
The purpose of this investigation was to examine the differences in PPWR, APWR, total WRK, and FI between RA younger adults and MA women during anaerobic cycling exercise. Master athletes were able to maintain performance values similar to the younger RA during handgrip and Wingate tests, whereas RA slightly outperformed the MA during the vertical power and isokinetic measures. This indicates that MA may be more comparable to RA than originally suspected in measures of physical performance (36).
Our study indicates that MA are able to produce similar power during a Wingate muscular power assessment as individuals half their age. Although it is inevitable that muscular power decreases with age, MA may be able to attenuate the natural declines by way of an active and competitive lifestyle (39). Petrella et al. (30) found that older women (≥60 years) produced a PPWR value 44% less than a younger cohort. Master athletes in our trials produced power rates that were only around 10% less than that of our younger RA cohort.
There were no differences between groups when observing handgrip strength. Handgrip strength is positively correlated with overall physical mobility in older adults (31,34) and has been found to decrease on average by 3 and 5% per year for men and women, respectively (5). Maintaining a grip strength that is not significantly different from those of younger age cohorts is an important indicator that maintaining physical activity levels in a competition-based environment with age can help preserve grip strength over the course of time.
The values observed for vertical power measures indicated significant differences between the RA and MA groups. However, when examining the percent differences between the RA and the MA regarding PVP and AVP, we found that the RA was superior to the MA by 9.2 and 16.4% for PVP and AVP, respectively. This indicates that the groups are actually quite close to one another than the values observed may have suggested. This is promising for MA as others have found that power differences between younger and older women were upward of 61% different in favor of the younger women (26) indicating that maintaining a physically active lifestyle throughout the course of one's lifetime allows for an attenuation of the decline in strength measures associated with age. The findings of lower-body power being extremely close between the MA and RA is an important piece in illustrating the importance of lower-body muscular power and strength. As we age, lower-body muscular power and strength are important because these are key factors in determining independence with age, if we lose too much we risk losing our independence (7).
An interesting aspect that did not have any significance between the RA and MA was the variable of FI. This indicates that the MA were able to maintain their level of performance in an anaerobic-based setting at the same rate as that of the RA. On a consistent basis, the RA performed, statistically, at a superior level on the isokinetic assessment when compared with the MA. However, when reviewing the percent differences between the groups, we noticed that the MA differences were small compared with RA. Although RA performed 15–30% superior on isokinetic measures, FI between the groups was only different by 4.4%. These findings indicate that although statistically significant from RA in some aspects, MA were still able to perform comparably to that of the RA. Master athletes' ability to produce performance values so closely related to RA, suggesting that being physically active on a regular basis attenuates age-related physiological declines.
Overall MA were similar to the RA women during the handgrip and Wingate tests, whereas RA slightly outperformed the MA during the vertical power and isokinetic measures This highlights the importance of MA training not only benefitting the outcomes of their competition but simultaneously attenuating the normal effects aging has on values of muscular strength, muscular power, and rate of fatigue when performing the exercise. These findings also indicate the importance of a physically active lifestyle and the benefits obtained that differentiate the MA not only from the RA but also from individuals in a similar cohort that do not adhere to a physically active lifestyle. Therefore, more research is needed that uses MA and RA to compare the different effects regular physical activity can have on the processes of aging using different variables.
Potential limitations that were outside the control of the researchers may have played a part in the results of the study. If the individuals had any change in their competitive playing time or extracurricular exercise regimens before the trial, there is a possibility the individual experienced transient muscle fatigue in the lower body. Differences in training schedules and length of sport participation could also have implications on outcomes for the variables assessed.
Because MA are an ever-growing population, it is important to understand the differences or similarities between them and their younger counterparts. These data allow for advancements in exercise training and performance outcomes for the MA population. Results from this investigation indicate MA can maintain anaerobic physical parameters similar to healthy, young women. This presumably allows for training protocols initially characterized for a younger athlete population to be adapted comparably for that of a MA population.
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