As an organic osmoprotectant and source of methyl groups betaine is involved in diverse cytoprotective and metabolically beneficial pathways in plants, animals, and prokaryotes [1, 2]. Recent human research has also examined the ergogenic potential of betaine in endurance and resistance exercise [3–6].

Armstrong et al. [3] reported non-significant trends (21% and 16%) toward longer sprint duration performed at 84% VO₂ max to volitional exhaustion in male runners following acute ingestion of 5 g betaine combined with water or a carbohydrate-electrolyte fluid, respectively, compared to corresponding control trials. In the only study published to date on the effects of prolonged (14-15 days) betaine supplementation (1.25 g twice per day) on power performance, Hoffman and coworkers [6] reported no significant differences between betaine and placebo groups in the total repetitions performed to exhaustion at 75% 1RM, or in the number of repetitions performed at 90% of both peak and mean power, in the bench press exercise. However, the number of repetitions performed in the squat exercise was greater (p < 0.05) on days 7-8 of betaine ingestion, and showed a similar trend (p = 0.06) on day 14-15, compared to the placebo group. There were no differences between groups in vertical jump power, in bench press throw power, or in the Wingate anaerobic power test.

Though little is yet known about the mechanisms, there is some evidence that betaine supplementation may positively affect exercise performance through favorable lactate and preferential fatty acid substrate metabolism [3, 5]. Additionally, betaine may be involved in defending intracellular volume [7, 8] and protecting enzymes of the citric acid cycle [2], which are challenged in progressive dehydration and hyperthermia associated with exercise. Less definitively, betaine's relationship to choline, methionine, serine, vitamin B metabolism, and methyl donating reactions may all contribute to its ergogenic efficacy [2].

Considering the known importance of dietary betaine, the safety of betaine supplementation [2], and prevalence of betaine in foods typical of affluent American diets [9], this study aimed to further investigate the yet undefined ergogenic effects of betaine on resistance exercise, particularly on strength and power performance. To this end, we conducted a carefully controlled randomized crossover design study using recreationally active men with at least three months of resistance training experience. We hypothesized that betaine supplementation would be associated with improved strength and power in these individuals, thus demonstrating the potential efficacy of betaine in improving performance and recovery in strength and power exercise.

Subjects reported that they could not distinguish which treatment (P or B) they received in either of the two phases of supplementation. All subjects reported similar physical activity and diet prior to each exercise test and throughout study participation. Subjects exhibited no significant change in weight over the course of the study, or between treatment periods (P Pre = 80.1 ± 10.5 kg, B Pre = 80.2 ± 11.5 kg, P Post = 80.3 ± 11.8 kg, B Post = 80.6 ± 11.3 kg).

Additionally, prior to each treatment phase, subjects exhibited no differences in hydration state determined by measures of urine specific gravity, averaging 1.019 ± .008 pre-testing during D1 and D2 for both the P and B conditions [13].

After 14 days of B supplementation, plasma betaine concentrations were significantly greater than corresponding baseline and placebo (48 ± 10 μmol/L) levels.

There were no differences in power output measures (W) for the four vertical jumps performed on D1 or Day 2 before P or B supplementation, or after 14 days of P supplementation. However, following the 14 days of B supplementation there were significant increases in power output for two of these four vertical jumps performed on D1 (4980 ± 61 and 5085 ± 137 W, respectively) and D2 (4811 ± 77 and 5068 ± 529 W, respectively) compared to corresponding D1 (4545 ± 114 and 4452 ± 130 W, respectively) and D2 (4476 ± 96 and 4848 ± 91 W, respectively) pre-supplement values.

Subjects exhibited decreased or similar force production in the isometric squat before and after P, but this was significantly improved on D1 and D2 after 14 days of B supplementation compared to pre supplement measures. Figure 1 illustrates these differences.

Squat jump power was not significantly different between P and B, nor was it different from pre- to post- testing for either treatment. There was also greater sample variation among individuals with respect to this test as can be seen in Figure 2.

Figure 3 shows improvements in isometric bench force following B supplementation. This B versus P difference was approximately 800 N greater on D1 and approximately 400 N greater on D2.

Figure 4 illustrates that bench throw power also significantly improved following 14 days of B supplementation on both D1 and D2 testing.

Hematocrit (%), hemoglobin (g/dL), and plasma osmolality (mOsm/kg) were significantly greater at post-squat (49 ± 1, 15.7 ± 1.0, 303 ± 4, respectively) and immediately after REC (48 ± 1, 16.0 ± 1.0, 303 ± 3, respectively) compared to pre-exercise values (43 ± 1, 14.3 ± 0.8, 289 ± 3, respectively) during D1 and D2 testing, but these values were not significantly different between the P and B trials.

Plasma glucose was not different before P or B supplementation (5.1 ± 0.6 and 5.0 ± 0.7 mmol/L, respectively) or at any time in response to the REC protocol (averaging 5.1 ± 0.5 and 5.1 ± 0.8 mmol/L, respectively) after P or B supplementation. As expected, plasma lactate showed significant increases above average pre exercise (1.4 ± 0.4 mmol/L) values throughout the REC protocol on both D1 and D2 testing days, and this increase (8.7 ± 2.2 and 8.8 ± 1.8 mmol/L, respectively) was the same for P and B exercise testing sessions.

There is an increased interest in the study of betaine as an ergogenic supplement for the neuromuscular system. In the current study, the primary effect of the betaine supplement was observed in the upper body, with enhanced bench press force and power production, but no change in the dynamic squat exercise performances. Additionally, the improvements in the bench press performances were observed on D2, demonstrating the efficacy of betaine as a potential aid to recovery. This is in contrast to the recent findings by Hoffman et al. [6] who demonstrated improvements in squat exercise endurance (i.e., number of repetitions to failure at 90% of the 1 RM yet not at 75% of the 1RM), but no changes in these measures in the bench press or for the lower body Wingate test. This disparity in results is likely due to a host of differences in the study design and dependent variables. Firstly, we utilized a within versus between group experimental design allowing greater control of statistical variance. Secondly, our study employed a different sequence of exercises and repetitions and our primary dependent variables were the peak force and power, rather than the force and power specific to local muscular endurance defined by the number of repetitions to failure at 75% and 90% of the 1RM. However, we did find that high force production improved with betaine supplementation which reflects some similarity to the study by Hoffman and coworkers. While the muscle groups in the two studies were apparently different in their mediating mechanisms, both studies provide evidence for the potential positive influence of B supplementation for strength, power and local muscular endurance in the context of demanding strength/power exercise protocols.

In the present study, the larger lower-body muscle group data was more varied within the subject sample and significant differences were less obvious, although patterns of B mediated increases may be suggested. For example, isometric squat force was enhanced by B supplementation. The REC protocol utilized maximal vertical jumps prior to the squat exercises which might have impaired the neuromuscular performance of high power production as recently noted by Drinkwater et al. [14], indicating that order of exercises is an important element in training program design. In this case, the betaine supplement was likely not able to offset the neural effect and partially explains the lack of improved power production in the squat. However, force production may have been facilitated via a post activation potentiation effect of some type [15]. While speculative, the upper body musculature was not inhibited by such an inhibitory neuromuscular influence of high velocity power movements as was the lower body in this exercise testing sequence. Thus, it appears that the mediating mechanisms of betaine supplementation may be more operational in the absence of high frequency neural fatigue.

From the non-significant differences in body fluid related variables between the B and P trials, due to the experimental controls for hydration employed in this study, it seems that betaine's established role as an osmoprotectant [2, 7, 8] was not a likely candidate for any ergogenicity. This does not, however, minimize the potential role of betaine given the intensity of the REC, as organic osmolytes have been shown to accumulate in cells under varying stressful conditions to help maintain biochemical function [16–18]. Additionally, plasma glucose and lactate results in this study indicate that betaine was either 1) not acting through glucose or lactate processing, or 2) the pre-existing differences among subjects masked any betaine effects on these dependent variables. The use of the very demanding REC might have overwhelmed the ability of betaine to offer any measureable differences, which in the case of the enhanced performances would most likely be related to phosphagen metabolism. Furthermore, the link between betaine as a methyl donor and improved exercise performance can only be speculated to be related to such variables as methionine, choline, and creatine [5, 19–23]. The contribution of betaine to these specific relationships should be examined in future studies.

Betaine has been shown to have numerous, diverse, positive effects [2] and in the current study betaine supplementation corresponded positively with gains in bench throw power, isometric bench press force, some measures of vertical jump power, and isometric squat force. However, precise mechanistic inferences will require further direct investigation while accounting for neural inhibitory factors. Considering the previous results from our laboratory demonstrating the effect of betaine on high intensity exercise performance in hot environments [3], and those recently reported by Hoffman et al. [6] on the quality of power test repetitions and endurance during power tests, it seems that betaine ergogenicity merits further research in both endurance and strength/resistance exercise.