Harris-Love MO, Davenport TE; National Institutes of Health, Clinical Center, Rehabilitation Medicine Department, PT Section, Bethesda, MD, USA. mlove@nih.gov.

PURPOSE: The purpose of this pilot study was to investigate the content validity of a physical performance battery of repeated functional tasks designed to assess anaerobic fatigue. BACKGROUND: Muscle performance cannot be characterized by peak torque alone as many functional activities involve repeated submaximal muscle contractions. While functional activities may be limited by anaerobic muscle fatigue, there is currently no validated physical performance test solely designed to assess this aspect of muscle performance. Therefore, a test of muscle endurance comprised of functional tasks was developed to assess fatigue. SUBJECTS: Four subjects (2 females, 2 males; mean age: 48.5 ±22.9) with stable idiopathic inflammatory myopathy (IIM) and 6 apparently healthy control subjects (3 females, 3 males; mean age: 49.5 ±14.1) participated in the study. METHODS: The Anaerobic Muscle Endurance (AME) test included 6 repeated functional tasks: placing an object overhead, sit-to-stand transfers, stair stepping, heel raises, sidelying press-ups, and bridges. All muscle performance measures were obtained with computer-assisted fixed dynamometry. Peak torque and total impulse fatigue index was measured during a 60-second maximal voluntary isometric contraction of the dominant shoulder flexors, hip extensors, knee extensors, and ankle plantarflexors. Perceived fatigue was assessed with the Fatigue Severity Scale (FSS) questionnaire. ANALYSIS: Spearman’s rho (ρ) was used to determine univariate correlations. The Mann-Whitney U statistic was used to compare group means. RESULTS: The AME test score and FSS mean score were significantly related (ρ= -.784, p<.01). The IIM group had significantly higher FSS mean scores and lower AME test scores than the control group (p=.01). Sit-to-stand performance was highly correlated with hip and knee extensor peak torque (ρ=.727 and .839, p<.02, respectively) and hip extensor FI (ρ= -.739, p<.02). Heel raises were highly correlated with the plantarflexion FI ( ρ = -.761, p=.01 ), but not plantarflexion peak torque (ρ=.214, p>.05). CONCLUSIONS: The AME test and FSS distinguished the IIM group from the control group. Significant levels of self-reported fatigue were related to decreased physical performance. However, anaerobic fatigue may surpass peak torque as a predictor of performance only when the task-specific threshold of muscle torque is exceeded. Sections of the AME test will require modification to better understand the fatigue-function relationship. FUNDING SOURCE: None.

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