Objective The objective of this study was to assess if individuals with osteoarthritis (OA) of the knee have reduced aerobic capacity compared with age and gender matched healthy controls. This study also assessed the accuracy of submaximal exercise testing for predicting aerobic capacity in individuals with OA.

Study design A cross sectional comparison study was undertaken with 24 participants with radiographic evidence of knee OA and 20 age and gender matched healthy participants within the control group.

Background OA of the knee is a musculoskeletal condition that affects a large number of individuals. With an aging population the incidence of OA is set to increase. OA is associated with pain, joint stiffness and reduced muscle strength. It has been demonstrated some years earlier that OA is associated with a reduction in aerobic capacity. This is thought to be as a result of reduced physical activity, and exercise avoidance. In recent years there has been increased emphasis on physical exercise as a treatment approach to OA, and a series of guidelines have been introduced to promote physical activity in elderly and diseased individuals. Theoretically the increased awareness of the benefits of exercise should result in improvements in aerobic capacity in individuals with OA. However, no studies have examined this.

As maximal effort exercise testing is expensive to undertake and requires significant training it is not practical in the clinical setting therefore submaximal effort exercise testing is a preferred alternative. However to date there have been no studies that provide evidence of the accuracy of submaximal exercise tests for predicting aerobic capacity in individuals with OA.

Method Forty four participants aged 47-81 years were recruited. Four participants were excluded from the study for failing to achieve two of the three determinants of aerobic capacity. Therefore total numbers for the study were 22 participants in the OA group (12 males, 10 females) and 18 participants in the control group (9 males, 9 females). Both groups had a mean age of 67 years with a SD of 10 years

A submaximal cycler ergometer test was utilised to predict aerobic capacity. Aerobic capacity was predicted from an equation that utilised exercise work rate (WR) and heart rate (HR) at the completion of the test.

A ramped cycle ergometer exercise protocol was used for the measure of maximal aerobic capacity. The incremental resistance for the test was calculated so participants reached maximal exertion between 8-12 minutes. A breath by breath analysis of expired gas, participant HR and perceived exertion was used to determine if maximal effort was reached.

Results There was a significant (P<0.05) reduction in aerobic capacity observed between individuals with OA of the knee (mean: 22 ml/kg/min) compared with age and gender matched healthy controls (mean: 27 ml/kg/min).

The mean predicted values from the submaximal test were 19ml/kg/min and 22ml/kg/min for the OA and control groups respectively. The submaximal exercise test under-predicted aerobic capacity in both groups. The Intraclass correlation coefficients (ICCs) were .75 and .72 for the OA and control groups respectively.

Conclusion The findings of this study are consistent with other literature indicating that individuals with OA of the knee have reduced aerobic capacity when compared with age and gender matched healthy controls. This study also indicates that submaximal exercise testing is a safe and accurate predictor of aerobic capacity in individuals with OA.