Associations of mechanical loading from physical activity with bone mineral density, physical function and knee impairment in older adults: the Tasmanian older adult cohort (TASOAC) study.

Abstract

Objective: Physical activity that induces high mechanical loading may benefit bone, but there are concerns of harm to joints in older adults. This longitudinal study aimed to investigate associations between loading intensities and application rates, estimated from selfreported physical activity, with bone mineral density (BMD), physical function, knee pain, knee cartilage defects and bone marrow lesions (BMLs) over 2.7 years. Method(s): 943 community-dwelling older adults (mean age 63.0 +/- 7.5 years) from the Tasmanian Older Adult Cohort (TASOAC) study were assessed at baseline and 2.7 years later. Selfreported physical activity over the past year was assessed using the Global Physical Activity Questionnaire (GPAQ; estimates metabolic equivalents of task or METs), from which loading scores (product of peak force and application rate) were estimated using previously reported load ratings for different activities. Hip and lumbar spine BMD was measured by dual-energy x-ray absorptiometry scans, dynamometry assessed knee extension strength and the Western Ontario McMaster Osteoarthritis Index (WOMAC) assessed knee pain, stiffness and dysfunction (higher scores indicate poorer outcomes). Magnetic resonance imaging measured cartilage defects and BMLs at the medial and lateral tibia and femur. Linear mixed models investigated associations between physical activity scores and outcome measures accounting for repeated measures. Result(s): Loading scores, but not METs, were significantly positively associated with femoral neck BMD (standardised beta = 5.49 mg/cm2 [95% CI = 0.09, 10.9 mg/cm2]) and knee extension strength (5.40 kg [0.13, 0.95 kg]) after adjustment for covariates including sex and body mass index. Neither loading scores nor METs were associated with spine BMD, WOMAC scores, knee cartilage defects or BMLs in unadjusted and adjusted models. Conclusion(s): In community-dwelling older adults, self-reported physical activity of high and rapid impact maintains higher femoral neck BMD and knee extension strength over 2.7 years without apparent deleterious effects on knee joint structure or pain.