Abstract
While training upregulates skeletal muscle Na+, K+-ATPase (NKA), the effects of knee injury and associated disuse on muscle NKA remain unknown. This was therefore investigated in six healthy young adults with a torn anterior cruciate ligament, (KI; four females, two males; age 25.0 ± 4.9 years; injury duration 15 ± 17 weeks; mean ± SD) and seven age- and BMI-matched asymptomatic controls (CON; five females, two males). Each participant underwent a vastus lateralis muscle biopsy, on both legs in KI and one leg in CON. Muscle was analyzed for muscle fiber type and cross-sectional area (CSA), NKA content ([3H]ouabain binding), and α1–3 and β1–2 isoform abundance. Participants also completed physical activity and knee function questionnaires (KI only); and underwent quadriceps peak isometric strength, thigh CSA and postural sway assessments in both injured and noninjured legs. NKA content was 20.1% lower in the knee-injured leg than the noninjured leg and 22.5% lower than CON. NKA α2 abundance was 63.0% lower in the knee-injured leg than the noninjured leg, with no differences in other NKA isoforms. Isometric strength and thigh CSA were 21.7% and 7.1% lower in the injured leg than the noninjured leg, respectively. In KI, postural sway did not differ between legs, but for two-legged standing was 43% higher than CON. Hence, muscle NKA content and α2 abundance were reduced in severe knee injury, which may contribute to impaired muscle function. Restoration of muscle NKA may be important in rehabilitation of muscle function after knee and other lower limb injury.
Highlights
Severe lower limb injury can substantially reduce lower limb function, leading to physical inactivity (Miyasaka et al 1991)
Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society
Values are Mean Æ standard deviation (SD). n = 4 KI, n = 4 CON. Combined denotes both type I and II fibers pooled. This is the first study to demonstrate that lower limb injury is associated with lower skeletal muscle NKA content and a2 relative abundance; these changes were coincident with lower thigh muscle cross-sectional area (CSA) and impaired muscle function, evidenced via reduced peak muscular strength
Summary
Severe lower limb injury can substantially reduce lower limb function, leading to physical inactivity (Miyasaka et al 1991). Some of the common debilitating effects of lower limb injury include decreased muscle size and strength, decreased joint proprioception, and increased postural sway (Willems et al 2002; Valderrabano et al 2006; Lee et al 2009). Together, these functional decrements adversely impact daily activities and quality of life in patients with lower limb injury (Frobell et al 2010; Heir et al 2010).
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