Equations Predict Quadriceps Strength in Knee Osteoarthritis

Equations based on submaximal strength are good measures of actual maximal strength

THURSDAY, Feb. 24 (HealthDay News) -- Predictive equations can be used to assess maximal quadriceps strength in individuals who have osteoarthritis in a knee joint, according to a study published in the February issue of Arthritis Care & Research.

Peter J. McNair, Ph.D., from the Auckland University of Technology in New Zealand, and colleagues assessed 18 patients with osteoarthritis of the knee to compare the accuracy of submaximal strength equations for predicting quadriceps strength. After one introductory session at a rehabilitation gym, participants returned to establish their maximal strengths (1-repetition maximum [1-RM]) for an open-chain knee extension and a leg-press exercise. At a final meeting the participants each exercised with a load that could be lifted about 10 times. The data were analyzed using 12 different prediction equations, to calculate the 1-RM strength, and compared to the 1-RM data established by the participants.

The investigators found that, for the knee extension exercises, prediction according to methods reported by Brown, Brzycki, Epley, Lander, Mayhew et al, Poliquin and Wathen had the highest level of accuracy; intraclass correlation coefficients (ICCs) were high, and errors were between 3 and 4 percent. For the leg-press exercise the highest levels of predictive accuracy were seen for measurements according to Adams, Berger, Kemmler et al, and O'Conner et al. The ICCs were high and typical errors low (5.9 to 6.3 percent).

"As knee extension and leg press are commonly employed in strengthening the quadriceps muscles, these findings are valuable to clinicians involved in exercise rehabilitation," the authors write.

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