The Effects of Small Changes in Power Output Below and Above the Maximal Lactate Steady State in Performance Fatigability in Older Females and Males

Purpose: In young adults, performance fatigability is affected by sex even with minor power output (PO) changes around the maximal lactate steady-state (MLSS). This study investigated whether these sex- and intensity-dependent effects persisted in older adults. Methods: 9 females (65±5 yrs) and 10 males (67±4 yrs) performed three 30-min constant-PO exercise bouts at MLSS, 10 W below (MLSS−10), and 10 W above (MLSS+10), each followed by a time to task failure (TTF) test at 80% peak-PO. Performance fatigability was assessed via knee extensor isometric maximal voluntary contractions (IMVC), voluntary activation (VA), and potentiated 100 Hz doublet torque (Db100) before, immediately after the constant-PO and the TTF bouts. Results: IMVC declined less after MLSS−10 (-18±8%) than MLSS+10 (-22±8%; p=0.04), but neither differed from MLSS (-20±8%). Similarly, Db100 decline was smaller at MLSS−10 (-14±6%) than MLSS+10 (-19±9%; p=0.03) but similar to MLSS (-15±0%). VA decreases were similar across all intensities (-6-7%; p>0.05). No sex differences were found for any fatigability variables (p>0.05). Despite the shorter TTF with increased in intensity at the end of each 30-min constant-PO (p<0.001), performance fatigability parameters at failure were similar across conditions (p>0.05), without sex-related differences. Conclusions: Unlike previous reports in younger populations, older males and females exhibited similar fatigability profiles after slight manipulations in PO around the MLSS, suggesting sex-based differences in muscular endurance diminish with age.