Do effects of verbal encouragement exceed day-to-day variability during strength and endurance performance testing in CrossFit-athletes? A randomized controlled crossover trial

Purpose: The aim of this randomized controlled crossover study was to investigate whether effects of verbal encouragement (VE) during strength and endurance performance testing in CrossFit-athletes occurs and, if so, would exceed day-to-day variability.
Methods: Nine-teen experienced CrossFit-athletes, 7 females (age 23.7 ± 3.9 years) and 12 males (age 23.7 ± 5.4 years), performed a standardized and typical 1 RM Crossfit squat test and a 12-minute endurance workout (as much repetitions as possible, AMRAP) on four different days over a 2-week period. Athletes performed the tests twice, either with VE or without (CON).
Results: Univariate comparison for mean squat strength revealed significantly (p = 0.009) higher strength values with VE (107 ± 33 kg) compared to CON (105 ± 33 kg). However, magnitude-based inference analyses revealed a most likely trivial effect in favour of VE for both strength and endurance testing. Very good to excellent relative day-to-day reliability (0.87< p <0.99) was observed for both strength and endurance parameters. Intraclass correlation values (ICC) were slightly higher for strength. Coefficient of variance (CoV) values for endurance with VE were slightly lower than for CON.
Conclusion: Despite reaching significance level, no meaningful effects of VE on strength or endurance have been found. CrossFit-specific strength and endurance performance testing proved to be very reliable. However, the trivial effects of VE do not notably exceed day-to-day variability during CrossFit-specific performance testing.