Methylphenidate alters brain connectivity after enhanced physical performance

ADHD Prescription Medications and Their Effect on Athletic Performance: A Systematic Review and Meta-analysis

BACKGROUND

Stimulant medications used for the treatment of Attention Deficit-Hyperactivity Disorder (ADHD) are believed to provide a physical advantage in athletics, but several of these medications are not regulated by the World Anti-Doping Association. Given the prevalence of ADHD among the athlete population and concern for abuse of ADHD medications, this review and meta-analysis aimed to evaluate effects of ADHD medications on athletic performance, thereby appraising the validity of claims of performance enhancement.

METHODS

A search of MEDLINE, Embase, CINAHL, and Cochrane Review databases was performed for all randomized controlled trials evaluating athletic performance after ingestion of placebo or ADHD treatment medications from August 2020 through November 2020. All RCTs identified from these search criteria were included for screening, with exclusion of any animal studies. Two reviewers (JB, CK) assessed methodological quality and risk of bias using CONSORT 2010 and Cochrane Collaboration tools. Study results were compiled with corresponding p values for each finding. Effect sizes (Cohen's D) for athletic performance and physiological changes were aggregated for each study. Studies were further screened for homogeneity that would allow for meta-analysis. Heterogeneity was calculated using I2.

RESULTS

A total of 13,033 abstracts evaluating amphetamine, methamphetamine, methylphenidate, and bupropion were screened. The final analysis included nine studies, six of which found significant improvement in athletic performance with use of stimulant medications (p < 0.05). Methylphenidate and amphetamine were consistently identified to have a performance effect. Secondary effects identified included significant increase in heart rate, core temperature, and elevation of various serum hormone levels (p < 0.05). Effect size evaluation found seven studies demonstrating small to large effects on physical performance, as well as in categories of cardiometabolic, temperature, hormone, and ratings of perceived exertion, to varying degrees. A meta-analysis was performed on two studies, demonstrating conflicting results.

CONCLUSIONS

Dopaminergic/noradrenergic agonist medications appear to have a positive effect on athletic performance, as well as effects on physiological parameters. Further consideration of medications currently not regulated, i.e. bupropion, is warranted given evidence of athletic performance enhancement. PROSPERO trial registration number: CRD42020211062; 10/29/2020 retrospectively registered.

On the functional connectivity between heart, muscle, and frontal brain cortex during exercise fatigability

We analyze the functional connectivity of the cortico-cardiac-muscular network during muscle fatigability due to exercise. For our experiments, we recruited ten volunteers who performed two cycling routines. Our volunteers were classified according to physical activity level as active or sedentary. First, we measured the electromyography (EMG) signal of the vastus lateralis muscle to find the volunteer's individualized physical workload capacity at the fatigue threshold. Two to three days later, we measured the volunteers' EMG, electrocardiography, and electroencephalography (EEG) data during the development of muscle fatigue with the individualized pedaling load previously obtained. We analyzed the EEG to identify the brain rhythm with highest power, then functional connectivity was assessed by computing the pairwise partial directed coherence of our measurements at such rhythm. Finally, we assessed significant changes in functional connectivity from start to finish of the exercise. Our results indicate that the sedentary group showed a significant decrease in connectivity, while the active group showed an increase in left-frontal connectivity. This might be explained in terms of frontal asymmetry phenomena which, for the case of active volunteers, may be a reflection of positive emotional states. Additionally, the active group showed increased self-regulatory processes in heart and muscle, while the sedentary group showed a decreased connectivity from heart to muscle together with a reduction in the muscle's self-regulation. These last results may be explained by a preference of the body in the sedentary group to attend vital requirements instead of exercise.

Structural brain differences between ultra-endurance athletes and sedentary persons

Participation in ultra-endurance events has increased in recent years and requires extreme levels of moderate to vigorous physical activity (MVPA). Moderate levels of MVPA have been associated with increased brain volume but the effects of extreme levels of MVPA on brain volume is unknown. As a result, we sought to compare the brains of those who engage in extremely high levels of MVPA with those who are sedentary using magnetic resonance imaging. We performed whole brain volumetric analyses and voxel-based morphometry on 12 ultra-endurance athletes (1078.75 ± 407.86 min of MVPA/week) and 9 sedentary persons (18.0 ± 56.9 min of MVPA/week). Whole-brain analyses revealed that those who participate in ultra-endurance training have increased grey (p< 0.0001), white (p = 0.031), and total matter volume (p < 0.0001), while regional analyses revealed that ultra-endurance athletes have smaller regional grey matter volume in the right primary sensory and motor cortex, inferior and middle frontal gyrus, and left thalamus. Future research is warranted to determine why ultra-endurance athletes have lower regional volumes in these areas despite having overall increased grey and white matter volumes.