Author(s): WEIPPERT, M., BIELITZKI, R.2, WELZ, M.1, SCHIFFER, J.1, HENNING, S.1, JOHN, H.1, SCHLEGEL, M.1, MAU-MOELLER, A.1, BRUHN, S.1, Institution: UNIVERSITY OF ROSTOCK, Country: GERMANY, Abstract-ID: 2246

INTRODUCTION:
Cognitive fatigue can negatively affect exercise intentions, performance as well perceived effort, pain, fatigue, and motivation. The menstrual cycle (MC) may further modulate these exercise related perceptions. However, it remains unclear whether caffeine can alter exercise intentions, behaviour, and perceived fatigue in women under cognitive fatigue and if the potential effect depends on the MC phase. This study investigated the effect of caffeine on exercise intention, performance and perceptual responses during a 30 min run or walk after a cognitively fatiguing task in young untrained eumenorrheic females during the late follicular (LF) or mid-luteal (ML) phase.
METHODS:
Using a randomized, double blind, placebo-controlled design, 34 females (LF group = 17, ML group = 17) completed a 50 min continuous performance task (CPT) to induce cognitive fatigue after receiving either caffeine (3 mg*kg-1) or placebo. Following the CPT, participants completed a 30-min treadmill run or walk at self-selected speed. Intended exercise intensity, covered distance as well as the temporal dynamics of perceived effort, affective valence, motivation, and fatigue during exercise were assessed. Data were analysed using a repeated-measures ANOVA with MC group as between-subject factor.
RESULTS:
Perceived cognitive fatigue increased after the CPT (p < 0.001; ηp² = 0.556) in both MC groups and conditions. Neither an effect of condition nor an interaction effect of condition × MC was evident for covered distance or the change in the intended exercise effort after the CPT. In contrast, a trend towards a condition × MC interaction was observed for perceived effort during exercise (p = 0.060, ηp² = 0.106). A significant condition × time × MC interaction was found for motivation (p = 0.003, ηp² = 0.131). Perceived motor fatigue during exercise was significantly lower in the caffeine condition (p = 0.034, ηp² = 0.133), with significant condition × time (p = 0.015, ηp² = 0.091) and condition × time × MC (p = 0.012, ηp² = 0.095) interactions. A significant condition × time interaction was found for affective valence (p = 0.038, ηp² = 0.076), while there was no interaction with MC (p = 0.869, ηp² = 0.010).
CONCLUSION:
Caffeine did not influence exercise intention and behaviour after a cognitively fatiguing task. In contrast, the decrease in affective valence during exercise was alleviated by caffeine. Furthermore, perceived effort and the decrease in motivation were lower after caffeine ingestion, but only in the ML group. Similarly, the mitigation of the exercise associated increase in perceived fatigue after caffeine ingestion was significantly more pronounced in the ML group. Thus, we cautiously conclude that the ergogenicity of caffeine under cognitive fatigue in women is limited to exercise-associated perceptions and – in part – dependent on the MC phase.