The choice of the outcome ( daily number of steps -LSB- STEPS -RSB- , time spent in at least moderate physical activity -LSB- TMA -RSB- , mean metabolic equivalents of task level -LSB- METS -RSB- , and activity time -LSB- ACT -RSB- ) , impact of weekends , number of days of assessment , postprocessing techniques , and influence of duration of daylight time ( DT ) on the sample size to achieve a power of @ were investigated .