The effect of caffeine chewing gum on muscle performance and fatigue after severe-intensity exercise: isometric vs. dynamic assessments in trained cyclists.

This study investigated the effect of caffeinated chewing gum (GUM_CAF) on muscle fatigue (isometric vs. dynamic) after severe-intensity cycling bouts. Fifteen trained male cyclists participated in four visits. Each visit involved two severe-intensity cycling bouts (Δ₁ and Δ₂) lasting 6 min, separated by a 5-min recovery period. Muscle fatigue was assessed by isometric maximal voluntary knee extension contraction (IMVC) with twitch interpolation technique and dynamically by 7 s all-out cycling sprints. Assessments were performed before GUM_CAF (Pre-GUM) and after the cycling bouts (Post-Exercise). GUM_CAF and placebo gum (GUM_PLA) were administered in a randomized double-blind procedure with participants receiving each gum type (GUM_CAF and GUM_PLA) during two separate visits. The results showed no significant interaction between gum types and time for the isometric and dynamic measurements (p > 0.05). The percentage change in performance from Pre-GUM to Post-Exercise showed no significant difference between GUM_CAF and GUM_PLA for either the dynamic-derived T_MAX (~ -17.8% and -15.1%, respectively; p = 0.551) or isometric IMVC (~ -12.3% and -17.7%, respectively; p = 0.091) measurements. Moderate to large correlations (r = 0.31-0.51) were found between changes in sprint maximal torque and maximal power output measurements and isometric force, for both gum conditions. GUM_CAF was not effective in attenuating muscle force decline triggered by severe-intensity cycling exercises, as measured by both isometric and dynamic methods. The correlations between IMVC and cycling maximal torque and power output suggest caution when interpreting isometric force as a direct measure of fatigue during dynamic cycling exercises.