Prediction of lower-limb isokinetic strength from functional fitness tests in older adults: A 550-participant cross-sectional study

Purpose: This study aimed to explore the association and prediction of hip abduction-adduction and knee flexion-extension isokinetic absolute and relative strength and power at 60°/s and 180°/s from functional tests performance (i.e., Up-and-Go Test [seconds], 30-Second Chair Stand Test [repetitions and relative and allometric power], 30-Second Arm Curl Test [repetitions], and 6-Minute Walk Test [meters]) in older adults.

Methods: Five hundred and fifty participants (404 women; age: 69.12 ± 5.29 years) enrolled in this cross-sectional study. Participants attended the laboratory once. Isokinetic concentric-concentric strength was assessed before physical fitness tests. Agility and dynamic tests were completed before strength and aerobic resistance tests within the physical fitness tests.

Results: Significant trivial-to-moderate correlations (positive and negative) were found between all the tests and the isokinetic strength and power of the knee and the hip. The performance in the UGT and 6MWT showed the best direct correlations with isokinetic strength and power (|r| = 0.09-0.48), and the 30CS and 30 AC showed inconsistent positive and negative correlations (r = -0.46-0.44). Significant regression equations including the functional tests, age, and sex were found, with higher values for knee isokinetic strength and power (R² = 0.19-0.44) compared to hip (R² = 0.09-0.35) and no clear pattern regarding better or worse predictability at higher angular velocities.

Conclusions: Isokinetic knee and hip strength and power are associated with functional fitness in older adults. The functional fitness tests, along with age and sex are predictive variables of older adults' lower-limb isokinetic strength, although explaining at most 44 % of the variance.