The number of aging individuals worldwide is increasing rapidly. By 2030, it is estimated that 20% of the U.S. population will consist of individuals aged 65 years or older (1), reaching about 65.7 million seniors (36). For older adults, maintaining a physically active lifestyle has been associated with an increased quality of life and ability to perform activities of daily living (26); however, as the aging process continues, many individuals, termed masters athletes (MA), have a desire to continue to participate in sport-based competition (18).
Participation in the United States Senior Games has increased over 500% since its inauguration in 1987 (25) and as this exponential influx in participation continues, so does the associated degree of competition (25). Unfortunately for MA, as they strive to compete against this growing field of athletes, they must also fight the decline in physical ability associated with the natural aging process. Even with intensive training, all performance indices decline with age (28), and certain aspects, such as strength, are even more difficult to maintain (35).
Between 40 and 50 years of age, muscle mass can decrease up to 8% (19) and strength declines at even faster rates (14). As a result, it becomes increasingly important for MA to find techniques to maintain and even increase physical performance. One method that has been used to increase anaerobic exercise performance is the use of supplemental beta-alanine (BA) (34). Physiologically functioning as the precursor to the dipeptide carnosine (6), BA is gaining ground as an ergogenic aid based on research indicating performance benefits from longitudinal (e.g., 28+ days, as acute doses have proven ineffective) supplementation on anaerobic performance (7,16). During exercise, carnosine functions as an intramuscular pH buffer, increasing removal of metabolic byproducts (H+) from lactate metabolism, and this increased buffering capacity will ultimately result in enhanced exercise performance lasting >60 seconds (17).
When examining the effects of BA on isokinetic exercise, subjects significantly increased torque production during the latter bouts of maximally exhaustive repeated knee extensions (7). However, this is in contrast to another investigation reporting no beneficial effects from BA on ISO (isokinetic) performance (20). Interestingly, the positive results reported by Derave et al. (7) were observed with an athletic male population, whereas those reported by Kendrick et al. (20) used an untrained male population. This possibly explains why Derave et al. (7) found ISO was improved with BA supplementation, as trained muscle is reported to have a more pronounced response to BA supplementation compared with untrained muscle (4).
When evaluating baseline levels of intramuscular carnosine, females have naturally lower levels compared with males (11) and experience greater relative increases in intramuscular carnosine from the same BA dosage (31). Taken together with the fact that trained muscle is more responsive to BA supplementation (4) and carnosine levels naturally decrease with advancing age (11), this suggests older trained females may exhibit augmented responses from long-term supplementation. Therefore, the purpose of this investigation was to evaluate the effects of 28-day BA supplementation on ISO performance, isometric strength, and body composition in female MA. It was hypothesized that 28 days of BA supplementation would improve isokinetic strength in female MA.
Experimental Approach to the Problem
The ergogenic effects of BA on exercise performance are well established in younger individuals; however, there is no evidence investigating these effects in masters-aged female competitors (age > 47 years). This investigation used a 2-group, double-blind, randomized design consisting of a 28-day supplementation intervention. To determine the efficacy of BA supplementation in female MA, subjects were randomly divided into 2 groups (n = 11 per group) and ingested the assigned supplement (placebo [PLA] = 8 g dextrose; BA = 800 mg + 8 g dextrose) 4 times per day throughout the 28-day intervention (totaling 3.2 g BA per day for subjects in the intervention group). ISO and HG were assessed at the baseline, 7-, 14-, 21-, and 28-day intervals. Dual-energy x-ray absorptiometry (DXA) was assessed at baseline and on the 28th day. Testing protocols were completed in the same order for all subjects.
Twenty-two female MA (all cyclists) from the southern United States participated in this investigation (Table 1). Cyclists were recruited as the push/pull nature of lower-body isokinetic exercise relates to muscle pattern activation used during cycling exercise (30). Masters athlete classification requirements were used based on those set forth by USA Cycling and World Masters Cycling. Masters athletes were required to fit the following criteria: (a) an age ≥30 years, (b) not classified as an elite cyclist or competitor in an elite event based on the international cycling federation (Union Cycliste Internationale, UCI) standards, and (c) not a member of a registered team under the UCI. Masters athletes must also have competitively cycled at least 2 years for 3 days per week (15). Although the USA Cycling and World Masters Cycling cutoff age for MA is ≥30 years, carnosine levels are significantly decreased 47 years of age (11); therefore, 47 was established as the age cutoff. All measures and protocols were approved by the institutional review board before testing and subjects reported to the Human Performance Laboratory on the University campus for all trials. Subjects were recruited through e-mail, fliers, and visits to local cycling clubs and organizations and were required to read and sign the approved University Institutional Review Board informed consent before participation.
Baseline testing was completed over 2 days. Day 1 consisted of signing an informed consent and completion of a health history questionnaire to ensure all subjects met the inclusion criteria. Body mass was assessed with a balance beam and height with a stadiometer (Detecto, Webb City, MO, USA). Body fat and lean mass were also measured by DXA (General Electric, Fairfield, CT, USA) on the initial visit. For the DXA, proper calibration procedures and quality assurance analysis were followed as previously described (13). Day 2 consisted of isometric handgrip strength (HG) and dominant leg ISO, in respective order. Subjects ingested the assigned supplement (PLA = 8 g dextrose; BA = 800 mg + 8 g dextrose) 4 times per day throughout the 28-day intervention (totaling 3.2 g BA per day for subjects in the intervention group). HG and ISO were assessed again at the 7-, 14-, 21-, and 28-day intervals. DXA was also reassessed on the 28th day. Testing protocols were completed in the same order for all subjects.
Subjects were instructed to maintain the same training intensity throughout the study and completed weekly exercise logs at the baseline, 14th, and 28th days. Investigators visually evaluated subject exercise logs to ensure subjects did not experience dramatic changes in training intensity. Food logs were distributed to all subjects at the baseline, 14th, and 28th days to be completed on 2 nonconsecutive weekdays and 1 weekend day (29) and analyzed for total kilocalorie and individual macronutrient consumption (Nutritionist Pro, Redmond, WA, USA). A 3-hour fast was required before each trial on testing days (33). All subjects had never ingested exogenous supplementary BA and refrained from vigorous exercise, alcohol, and caffeine 24 hours preceding each trial. Subjects replicated similar attire for all trials and were allowed to use their own shoes and clips.
Subjects were randomly assigned to either PLA or BA groups. As previously recommended for good practice in supplement research (17), the BA provided for this investigation (Powder City, York, PA, USA) was third-party laboratory tested for supplement purity and authenticity. To ensure the double-blind design was maintained, a separate investigator not participating in the data collection process completed supplement assignments. Conditions included PLA (8 g dextrose, 4 times per day) or BA (800 mg BA + 8 g dextrose 4 times per day). Individual doses of 800 mg were used to circumvent the potential occurrence of paresthesia (20,21), which would ultimately remove the double-blind design. Subjects were instructed to consume the supplement in 16 ounces of water (32).
Isometric Grip Strength Testing
HG testing was used as a measure of isometric strength because it is highly correlated with overall strength (23). All HG measurements were administered by a trained technician and measured in kilograms using a hand-held dynamometer (Creative Health Products, Ann Arbor, MI, USA). All measurements were performed on the dominant hand with the subject standing, arm down at the side, wrist in neutral position, and interphalangeal joint of the index finger maintained at 90°. Subjects maximally squeezed the handle for 5 seconds as standard encouragement was provided. The test was repeated 3 times on the dominant hand with 60-second rest between attempts. The greatest of the 3 attempts was used as the final strength measurement. High test-retest reliability (intra-class correlation [ICC] = 0.95) for the HG strength test has been previously recorded (5).
Isokinetic Strength Analysis
The Biodex system II Isokinetic Dynamometer (Biodex Medical, Inc., Shirley, NY, USA) measured ISO using a 50-repetition protocol with 240° eccentric/180° concentric movement parameters. Subjects sat upright with the dynamometer axis of rotation aligned with the axis of rotation of the dominant knee. Secured belts stabilized the trunk, pelvic girdle, and thigh to the Biodex chair to prevent additional body movement. The chair and dynamometer settings were recorded to ensure positioning for all testing remained the same between trials. Before testing, the dominant limb was weighed, so that it could be added and subtracted from torque values when working against and with gravity, respectively. Subjects fully extended and flexed the knee maximally during the 50-repetition testing period. To ensure maximal effort was given during the evaluation, strong verbal encouragement was provided throughout each testing session (3). All outcome variables were calculated using the Biodex system II Isokinetic Dynamometer software. Validity (8) and reliability (ICC = 0.95–0.97) (12) of the Biodex system II Isokinetic Dynamometer have been previously demonstrated. Before testing, calibration of the dynamometer was performed according to manufacturer specifications.
Blinding Efficacy and Side Effects
On completion of the 28-day intervention, subjects were asked which supplement they believed that they had consumed. Subjects were also asked whether they experienced any side effects throughout the course of the study related to the supplement ingested.
SAS version 9.4 (Cary, IN, USA) was used to analyze all data. To assess the effects of supplementation on HG and ISO variables between groups, investigators used within and between repeated-measures analyses of variance (ANOVAs) (group [2; BA vs. PLA] × time [5; baseline, weeks 1, 2, 3, and 4]) for each variable. For statistically significant F scores, simple main effects were analyzed with factorial ANOVAs for each time point. An alpha level of p ≤ 0.05 defined significance. To determine the participant's ability to determine which supplement they had ingested through the design, Fisher's exact test (2 [supplement guess] × 2 [accuracy]) was used. All data were reported as mean ± SE.
There were no initial significant differences between groups for demographic variables (Table 1). When examining dietary logs between BA and PLA, no significant differences were observed for overall total kilocalorie intake or individual macronutrient breakdowns (carbohydrate, fat, protein) within or between groups at any time point (Table 2).
Isokinetic Lower-Body Exercise
There were no significant differences at baseline between groups for all flexion and extension variables measured during ISO (Table 3, p > 0.05). Repeated-measures ANOVA revealed that there was a significant group-by-time interaction during the extension component for average peak torque generated throughout the test (p = 0.012) and the flexion component for total work performed during the final third of the exercise assessment (p = 0.008). When comparing BA and PLA, at 28-day time point, average peak torque (F = 7.398, p = 0.014; 8.1 vs. 1.4% change, respectively) and total work performed during the final third of exercise (F = 5.942, p = 0.024; 24.0 vs. −16.8% change, respectively) significantly increased from baseline (Figures 1 and 2, respectively). No differences existed for any variable during the intermittent weeks (p > 0.05).
Isometric Grip Strength
Handgrip strength was not affected by BA supplementation (Table 4). Repeated-measures ANOVA indicated that there were no group-by-time interactions throughout the course of the 28-day intervention (F = 0.62, p = 0.65).
Body composition (regional and total) was also not affected by longitudinal BA supplementation (Table 5). Repeated-measures ANOVA indicated that there were no group-by-time interactions throughout the course of the intervention (all p > 0.05).
Blinding Efficacy and Side Effects
Fisher's exact test indicated that the subjects were unable to accurately assess which supplement they had consumed based on a 2 (supplement guess) × 2 (accuracy) analysis (p = 0.31). Accurate guesses for the BA, and PLA groups were recorded as 23 and 32%, respectively. Only 1 subject reported feelings of paresthesia throughout the course of the intervention. All analyses were conducted with and without the subject who experienced side effects during the trials. No changes were detected for any analysis, and as a result, the subject was included in the final statistical models.
This is the first study evaluating the longitudinal effects of BA supplementation on isokinetic exercise, isometric grip strength, and body composition in female MA. Results from this investigation indicate that exogenous BA supplementation in female MA increases indices of lower-body ISO, without subsequent changes in HG or body composition.
The increases in ISO indices among female MA were unique to the current investigation. Previous data examining BA as an aid to increase isokinetic strength have been inconclusive (7,20); however, these previous results were collected from males of differing training levels. In the current investigation, female MA experienced significant increases in lower-body ISO after the 28-day BA intervention. Subjects consuming BA increased average peak torque (8% from baseline) and total work performed during the final third of exercise (24% from baseline) compared with age-matched controls consuming PLA. As average peak torque is the overall average of the peak torque measurements from each repetition performed throughout the isokinetic testing protocol, this indicates that cyclists consuming BA for 28 days were able to maintain a higher peak torque for each repetition compared with PLA. Work performed during the final third of exercise also significantly increased after 4 weeks of BA supplementation, indicating female MA were able to produce more work during the latter component of ISO. Results from this study were in line with the work by Derave et al. (7) indicating BA supplementation significantly increases ISO performance, but contradictory to the work of Kendrick et al. (20). The reason for the discrepancy between the studies may be attributed to the training status of the subjects involved, as Derave et al. (7) used trained subjects, whereas Kendrick et al. (20) evaluated previously untrained males. Of further interest is the fact that Derave et al. (7) actually used a lower supplementation dose (4.8 g·d−1) compared with Kendrick et al. (20) (6.4 g·d−1) over the same 28-day protocol. This increases support for the previously reported concept that training status may play a significant role regarding the effectiveness of BA supplementation (4), as similar significant results were observed in the current investigation when using trained masters-aged females.
As previously mentioned, BA supplementation directly increases intramuscular carnosine (9), which ultimately increases the ability to remove byproducts (H+) of lactate metabolism (6). Therefore, these increases in ISO performance were most likely due to an increased buffering capacity directly related to elevated carnosine concentrations (27).
Although ISO improved through longitudinal BA supplementation, there were no significant effects on isometric grip strength among female MA. It has been proposed that increases in intramuscular carnosine can have beneficial physiological effects on exercise outside of increased buffering capacity (17). One of these benefits is an increase in Ca2+ sensitivity of the muscle fibers, potentially leading to greater force of contraction (10). However, this did not translate into increases in handgrip strength at any time point during the intervention. This may have been because the evaluation was not long enough to elicit the onset of fatigue (as with the ISO exercise); therefore, future investigations should use longer duration isometric evaluations when examining this component of BA supplementation.
Analogous to previous investigations (20,22,29), longitudinal BA supplementation demonstrated no significant changes in body fat percentage among female MA. Although our results were similar to the aforementioned studies (20,22,29), it is important to note that each previous investigation used male subjects with healthy percentages of body fat (24). Estimated averages from each study were as follows based on reported subject demographics at pretesting: Smith et al. (29), = 14.9%, Kern and Robinson (22), = 8.7%, and Kendrick et al. (20), = 10.2%.
The overall results of this study were based on the premise that performance increases during ISO directly relate to increases in concentrations of intramuscular carnosine, although it is important to note carnosine was not directly measured in this investigation. It has been well established that consumption of BA significantly increases carnosine concentrations after at least 28 days of supplementation (16,21), and the current investigation used a dosing protocol previously reported to be effective for these increases to occur (17). Another limitation included the collection of dietary and exercise information. Although subjects reported maintenance of regular training programs and dietary analyses revealed no differences between BA and PLA groups for total kilocalorie or macronutrient intakes, this is reliant on accurate recordings and honesty by the subjects.
Longitudinal (28 days) BA supplementation (3.2 g per day) in female MA increased lower-body ISO, independent of changes in HG or body composition. Although carnosine was not directly measured in this investigation, it can be hypothesized that increases in the dipeptide from exogenous BA consumption was responsible for the beneficial effects on ISO. Because intramuscular carnosine is lower in females and aged individuals (11), female MA represent a population that may be more sensitive to increases in carnosine from BA supplementation and subsequently lead to improvements in exercise performance.
The primary results of this study suggest that BA (1.6 g per day) for 28 days is an effective method for increasing lower-body ISO. The use of BA supplementation seems to be well tolerated with minimal side effects related to long-term use. As a result, it provides a feasible method with which to increase strength performance, specifically in female MA cyclists. Cyclists are constantly pedaling throughout competition, and this pedaling intensity increases near the race's end (2). The ability to generate increased peak torque during not only an individual repetition but throughout multiple pedaling repetitions (as replicated by the ISO exercise in our study) could potentially lead to an increase in overall performance times. This is also important for cyclists as they near the end of a race when anaerobic metabolism is predominantly used in an attempt to hold or advance their finishing position. The ability to produce more work toward the end of a race may also potentially allow competitors to increase performance times due to increased sprinting ability.
The authors thank Powder City for donating the beta-alanine used in this investigation. They also thank Mikaila Davis, Aaron Martinez, Landon Lavene, Carly Arnold, and Lauren Wethington for their help with study preparation and during collection of data. The authors declare they have no conflicts of interest associated with this investigation. The results of this study do not constitute endorsement of the BA used in this investigation by the authors or the National Strength and Conditioning Association.
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