The effect of 6-day fasting on physical performance and neuromuscular control in healthy men

Understanding physical functioning during fasting is critical for both survival and everyday performance. Thus, the main aim of the present study was to determine the effects of a 6-day fasting period on fine motor skills, drop jump (DJ) performance, and neuromuscular properties of the ankle plantar flexors in healthy, physically inactive men. Non-obese men (n = 14) completed a 6-day fast followed by 7 days of habitual diet. Changes in mood state, fine motor skills, reflexes (V-wave, H-wave and M-wave), involuntary muscle torque, maximal voluntary contraction (MVC), central activation ratio (CAR) during MVC, and DJ performance were measured. Fasting had no effect on physical performance (i.e., fine motor skills and DJ) and MVC; however, it increased subjective perceived fatigue, and reduced the H_max/M_max and V_sup/M_max amplitude ratios after both 4 and 6 days of fasting (P < 0.05). In contrast, a decrease in CAR and an increase in H-reflex latency were observed only after 6 days of fasting (P < 0.05). Following the return to a habitual diet, CAR and reflexes returned to prefasting values (P > 0.05), while improvements in mood, including decreased perceived fatigue and depressive symptoms, and increased vigor were accompanied by enhanced fine‑motor performance (P < 0.05). To conclude, despite adaptive modifications at both supraspinal and spinal levels and increased fatigue, MVC, jump performance, and fine‑motor skills were preserved after prolonged fasting. After resuming a habitual diet, changes at supraspinal and spinal level returned to baseline, and mood improvements coincided with enhanced fine-motor performance.Trial registration Retrospectively registered on ClinicalTrials.gov (NCT05545943).