The effect of obesity on central activation failure during ankle fatigue: a pilot investigation

Background: In a forward-directed oscillation, individuals who are obese may be at higher risk of falls due to weaker ankle dorsiflexor muscles as the prime controllers of the balance recovery. Muscle recovery may be negatively affected by fatigue at either the central (activation) and/or peripheral (contraction) levels. Additional body weight support, as required with obesity, may increase lower extremity muscle fatigue development. Purpose: The objective of this pilot study was to quantify the relationship between body mass index (BMI) and fatigue symptoms quantified as endurance time, torque loss, and central activation failure for the tibialis anterior. Methods: Twenty-two young males (mean BMI = 27.0 kg/m²; range: 20.5–36.7 kg/m²) completed maximum voluntary isometric contractions (MVICs) of the ankle dorsiflexors before (pre-MVIC) and after (post-MVIC) a sustained isometric fatiguing task at 60% of their strength. Electrical stimulation was superimposed during each MVIC to identify central activation failure. Results: Pre-fatigue central activation was equivalent across participants. However, BMI and pre-MVIC explained 59% of the variation in central activation failure after the fatiguing task as well as 29% of the variation in endurance time. In fact, a significant effect of obesity on central activation failure was observed with fatigue. Finally, 43% of the torque loss following fatigue variation was explained only with pre-MVIC. Conclusions: The findings of this pilot investigation indicate that endurance and central activation after fatigue may be impaired with increased BMI. This finding may aid in the evaluation of falls mechanisms and the development of falls prevention strategies.