Daily physical activity behavior: a compensatory factor to physical adaptations variability following a 12-week power training in older men

Physical activity (PA) is effective to counteract age-related declines. However, inter-individual variability in training adaptations may limit prediction of individual responses and intervention optimization. Daily PA behavior may contribute to this variability. The objective was to examine daily PA behavior through a 12-week supervised power training (PT) and its associations with clinical adaptations in 36 older men. Time of PA, step count, total (TEE) and active (AEE) energy expenditure, metabolic equivalents of task (METs), and sedentary time were assessed using a 3D accelerometer for three days surrounding PT sessions (Day-PT-1, Day-PT and Day-PT+1) at pre-(T0) and mid-intervention (6-week; T6). Physical performance, body composition and muscle function were assessed pre-(T0) and post-(T12) intervention. PA behavior outcomes did not change between T0 and T6, except for METs which decreased by 0.2 METS (T0:1.44{+/-}0.34 vs. T6:1.25{+/-} 0.18; p=0.003 [13%]). At T6, day-to-day fluctuations were observed for PA behavior on Day-PT-1 and Day-PT+1 compared with Day-PT (all ps<0.05). Following the intervention, body composition and muscle characteristics improved significantly. Between T6-Day-PT-1 and T6-Day-PT, greater increases in time of PA were associated with lower Fast Timed Up and Go speed adaptation (p=0.02), and greater reductions in step count were associated with greater reductions in muscle power (p=0.02). Finally, increases in step count and time of PA were associated with greater upper limb strength (p=0.04) and muscle pennation angle (p=0.02). PA behavior appears modulated during a 12-week PT intervention in healthy older men. Thus, PA behavior surrounding training sessions could be an important compensatory factor contributing to adaptations variability.