Physical Working Capacity at Fatigue Threshold (PWC_FT) is Associated with Sarcopenia-Related Body Composition and Measures of Functionality in Older Adults

The relationship between physical working capacity at fatigue threshold (PWC_FT) and common measures used to assess sarcopenia in older adults were examined. Fifty-eight older adults (age: 71.1±6.2 y; BMI: 28.0±5.4kg/m²) completed the testing procedures. Sarcopenia-related body composition was measured by dual-energy x-ray absorptiometry and participants performed a discontinuous cycle ergometry test to determine PWC_FT. Functionality assessments included maximal isometric grip strength (GRIP) and sit-to-stand (STS) repetitions in 30seconds. Muscle quality (MQ) was defined as GRIP relative to appendicular lean soft tissue (ALST), while skeletal muscle index (SMI) was defined as ALST/height². Pearson correlations were used to examine the relationships among dependent variables. PWC_FT showed significant relationships with ALST (r=0.57), SMI (r=0.47), body fat percentage (r=-0.50), GRIP (r=0.49), and STS (r=0.44). For follow-up analyses, study participants were categorized into low sarcopenia risk (n=31) or high sarcopenia risk (n=27) groups by SMI. Sarcopenia risk was associated with PWC_FT [odds ratio (OR): 1.051, 95% confidence interval (CI): 1.016-1.087] and STS (OR: 1.305, CI: 1.060-1.607), but not GRIP (OR: 1.098, CI: 0.989-1.218). Using receiver operator characteristic curve analysis, both PWC_FT [area under the curve (AUC): 0.737, CI: 0.608-0.866, optimal cutoff: 37.5 watts] and STS (AUC: 0.749, CI: 0.623-0.874, optimal cutoff: 12.5 repetitions] showed discriminative ability with regard to sarcopenia risk. The current data suggest that the neuromuscular fatigue threshold, as measured by PWC_FT, is related to measures of body composition and function in older adults.