Predicting the ergogenic response to methylphenidate.

PURPOSE: Methylphenidate (MPH) and other stimulants have been shown to enhance physical performance. However, stimulant research has almost exclusively been conducted in young, active persons with a normal BMI, and may not generalize to other groups. The purpose of this study was to determine whether the ergogenic response to MPH could be predicted by individual level characteristics. METHODS: We investigated whether weekly minutes of moderate-to-vigorous physical activity (MVPA), age, and BMI could predict the ergogenic response to MPH. In a double-blind, cross-over design 29 subjects (14M, 15F, 29.7 ± 9.68 years, BMI: 26.1 ± 6.82, MVPA: 568.8 ± 705.6 min) ingested MPH or placebo before performing a handgrip task. Percent change in mean force between placebo and MPH conditions was used to evaluate the extent of the ergogenic response. RESULTS: Mean force was significantly higher in MPH conditions [6.39% increase, T(25) = 3.09, p = 0.005 118.8 ± 37.96 (± SD) vs. 111.8 ± 34.99 Ns] but variable (coefficient of variation:163%). Using linear regression, we observed that min MVPA (T(25) = -2.15, ß = -0.400, p = 0.044) and age [T(25) = -3.29, ß = -0.598, p = 0.003] but not BMI [T(25) = 1.67, ß = 0.320 p = 0.109] significantly predicted percent change in mean force in MPH conditions. CONCLUSIONS: We report that lower levels of physical activity and younger age predict an improved ergogenic response to MPH and that this may be explained by differences in dopaminergic function. This study illustrates that the ergogenic response to MPH is partly dependent on individual differences such as habitual levels of physical activity and age.

Methylphenidate alters brain connectivity after enhanced physical performance.

Muscle fatigue is a disturbed homeostatic state characterized by a temporary inability to maintain force output and has lasting effects on the brain in the period immediately after exercise, such as decreased interhemispheric functional connectivity (FC). Stimulants that increase dopamine and norepinephrine neurotransmission can enhance performance during muscle fatiguing exercise (i.e. are ergogenic). We recently demonstrated that methylphenidate (MPH) increased force output and increased FC between the insular (IC) and hand motor cortex during a fatiguing handgrip task. However, whether resting FC is altered in the recovery period after enhanced force is unknown. The objective of these follow-up analyses was to examine the effects of performing a fatiguing handgrip task with MPH on subsequent resting state FC. In a double-blind counter-balanced design, participants ingested placebo or MPH and in a magnetic resonance imaging scanner performed: a six-minute pre-task resting scan, a fatiguing handgrip task during scanning, and then a six-minute post-task resting scan. We investigated task-related force and resting state FC pre- and post-task between: (1) interhemispheric motor cortices (M1) and (2) the right IC and left hand motor area. We found 1) a post-task reduction in M1 interhemispheric FC and that the extent of reduciton was negatively correlated with enhanced mean trial force in MPH conditions. 2) MPH but not placebo increased post-task FC between the right IC and left hand motor area. This study demonstrates that using MPH during a muscle fatiguing task has lasting effects on the brain that are markedly different from drug naïve conditions.

The COMT val(158)met polymorphism in ultra-endurance athletes.

UNLABELLED: Chronic levels of physical activity have been associated with increased dopamine (D2) receptors resulting in increased sensitivity to dopamine release. The catechol-O-methyltransferase enzyme, responsible for dopamine degradation, contains a functional polymorphism, which plays an important role in dopamine regulation within the prefrontal cortex. This polymorphism has previously been shown to affect human cognition and personality. However, the effect of this polymorphism has not been shown in ultra-endurance athletes. AIM: To examine the association of the COMT val(158)met variant with personality traits (harm avoidance, novelty seeking, reward dependence, resilience) and psychological distress (K10) of habitual physically active Ironman athletes compared to recreationally active controls. METHODS: 51 ultra-endurance Ironman athletes and 56 recreationally active controls were genotyped for the catechol-O-methyltransferase val(158)met polymorphism. Of the 107 participants, 55 ultra-endurance athletes and 32 recreationally active controls completed online personality questionnaires (harm avoidance, novelty seeking, reward dependence, resilience) and a psychological distress questionnaire (K10). RESULTS: The personality trait, harm avoidance (p=0.001) and psychological distress (p=0.003) were significantly lower in Ironman athlete participants. Novelty seeking was significantly higher (p=0.02) in Ironman athlete participants with a significantly higher (p=0.04) score in Met(158) homozygous allele carriers. CONCLUSION: Chronic levels of physical activity, as seen in ultra-endurance athletes, show increased novelty seeking scores in Met(158) homozygous allele carriers.