N.L Hunt, M.V Robinett, T.N Brown

Boise State University, Boise, ID

Strong, steady knee extensor contraction may slow development and progression of degenerative knee joint disease, especially following injury. PURPOSE: To determine if knee injury and disease impact extensor contraction strength and steadiness. METHODS: Forty clinical (self-reported knee musculoskeletal injury or disease) and healthy (no reported injury or disease) young (18 to 35 years) and older adults (> 65 years) participated. Participants performed three 5 second knee extensor maximal isometric contractions. Contraction with greatest torque was used to quantify knee extensor strength (peak torque, rate of torque development - RTD), and time (coefficient of variance in torque magnitude - CV), and frequency domain (peak power frequency - PPF and total power) steadiness measures. Non-parametric statistical analysis was used to assess cohort (clinical young and older adults, healthy young and older adults) differences and relation between strength and steadiness measures. RESULTS: Young adults had stronger knee extensors. Healthy and clinical young adults exhibited greater peak extensor torque and RTD compared to clinical older adults (all: p<0.016); while clinical young adults exhibited greater peak torque than healthy older adults (p=0.028). Healthy and clinical young adults exhibited greater total power (p<0.019) compared to clinical older adults. Clinical young adults were less steady (greater PPF) than healthy young adults (p=0.046). Knee extensor strength and steadiness were related. Peak extensor torque exhibited significant positive relation with RTD (ρ=0.668) and total power (ρ=0.683) (both: p<0.001), and both RTD and knee extensor CV a significant positive relation with total power (ρ=0.656; p<0.00; ρ=0.342, p=0.028). CONCLUSION: Age and knee musculoskeletal conditions alter extensor neuromuscular function. Unsurprisingly, young adults were stronger than older adults. Yet, clinical participants (young and older) exhibited muscle dysfunction or less steady extensor contraction that may alter knee joint loads, resulting soft tissue degradation during routine weight-bearing activities. Practitioners may target restoration of muscle strength and steadiness to impede joint disease development and progression during rehabilitation programs.

*Supported by NIH NIA and NIGMS.

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