Author(s): DEL VAL MANZANO, M., MONTALVO-ALONSO, J.J., LÓPEZ-SAMANES, A., MARTÍN-LÓPEZ, J., VALADÉS, D., FERRAGUT, C., PÉREZ-LÓPEZ, A., Institution: UNIVERSIDAD DE ALCALÁ, Country: SPAIN, Abstract-ID: 2072

INTRODUCTION:
Neuromuscular performance variations have been reported at different times of day in different sports modalities. The morning reductions in performance can be observed in complex and continuous motor control tasks (e.g., tennis serve or swimming), but the changes in motor performance associated with circadian rhythm have been mostly described for long- and medium-term effects, mainly depending on endurance performance. However, how the circadian rhythm affects short-term events that rely on muscle strength and power output remained poorly studied. Therefore, this study aimed to examine the effect of the time of day on muscular strength, power and endurance in resistance-trained individuals.
METHODS:
Thirteen resistance-trained males (age: 26.3±6.7 years; resistance training experience: 4.3±3.1 years; 1RM/kg bench press: 1.22±0.21; 1RM/kg back squat: 1.82±0.32) participated in a randomized cross-over and counterbalanced trial, performing in the morning (9:00h) and the evening (18:00h) a muscular strength and power assessment for bench press and back squat exercises at 25%, 50%, 75%, 90% and 100% of 1RM, performing 3, 2, 1, 1 and 1 repetitions, respectively. Muscular endurance was then assessed for both exercises at 65% 1RM, performing one set until task failure.
RESULTS:
In muscular strength and power, no statistically significant differences between groups (morning vs evening) or interaction (group by load) were found in the bench press or back squat exercise for mean, peak and time to reach peak velocity and power output (ANOVA, P>0.05). Only, in the back squat exercise, higher performance was found in the evening compared to the morning at 25%1RM in mean (13%, 1084+/-259 vs 956+/-163 W/kg, P=0.031, g=1.91) and peak power output (11%, 2417+/-450 vs 2183+/-262 W, P=0.018, g=2.2). Similarly, in muscular endurance, no statistically significant differences were found between morning and evening trials for the number of repetitions, mean, peak, time to reach peak velocity, and power output (P>0.05).
CONCLUSION:
Some evidence suggests a performance reduction in complex motor control tasks involving muscular power (e.g., tennis or volleyball) in the morning compared to the evening. However, in this study, no differences in muscular strength, power, or endurance were found in the bench press or back squat exercises performed from 25% to 100% of 1RM. Therefore, if circadian rhythm affects short-term tasks, this effect may occur in action performed with light loads (<25%1RM).