Influence of physical activity-related joint stress on the risk of self-reported hip/knee osteoarthritis: a new method to quantify physical activity

Abstract

Background

The relationship between physical activity (PA) and the development of hip/knee osteoarthritis (OA) has not been clearly defined. The purpose of this study was to develop a method to quantify PA-related joint stress and to assess its influence on the risk of hip/knee OA.

Methods

Participants in a large longitudinal study, without knee/hip OA (n = 5284), were asked about their PA participation in 1986. PA-related joint stress was calculated using information on the frequency, intensity, and duration of individual types of PA, and incorporated a quantification of joint stress. Self-reported, physician-diagnosed hip/knee OA was ascertained by survey in 1990, 1995, and 1999 (average length of follow-up: 12.8 years).

Results

The joint stress PA score was not associated with an increased risk of hip/knee OA. Also, among walkers and runners there was no association between the frequency, pace, or weekly training mileage and hip/knee OA. Older age, previous joint injury and surgery, and higher body mass index were confirmed as independent risk factors for hip/knee OA.

Conclusions

Participation in PA as an adult does not increase the risk of hip/knee OA and there does not seem to be a threshold of increasing risk with increased training among walkers and runners.

Introduction

The health effects of physical activity, which are numerous and well known, include increased longevity and decreased incidence of cardiovascular disease, diabetes, obesity, and hypertension, among others [1], [2], [3]. In 1995, the Centers for Disease Control and Prevention and the American College of Sports Medicine released their joint recommendation for all U.S. adults to accumulate at least 30 min of moderate-intensity physical activity on most, if not all, days of the week [1]. An example of moderate activity is brisk walking at 3 to 4 miles per hour. Little consistent information is available in the scientific literature regarding the potentially hazardous effects of physical activity such as osteoarthritis (OA) [4]. In light of the national physical activity recommendations, it is important to define what effect increased physical activity levels may have on the development of osteoarthritis.

OA is one of the most prevalent chronic diseases, affecting more than 20 million persons in the United States [5]. Known risk factors for both hip and knee OA include female gender, age, obesity, previous joint injury, education level, and occupational activities [6], [7], while hormone replacement therapy and smoking have been shown to be protective [7], [8], [9], [10]. To date, the relationship between physical activity and subsequent OA has not been clearly defined. Studies among special populations of elite athletes as well as the general population indicate that long-term vigorous physical activity and specific, strenuous sport participation increase the risk of developing hip and knee OA, supporting the “wear and tear” theory of joint degeneration related to repetitive joint loading [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21]. Other studies report no significant increased risk of OA from moderate and vigorous physical activity including recreational running [12], [18], [22], [23], [24], [25], [26], [27], [28], [29].

Many of the previous studies investigating the association between physical activity and OA have been limited by the use of a cross-sectional or case–control study design, a lack of detailed physical activity and injury data, and/or an inability to capture incident OA. An additional, important limitation is that no prior studies investigating the relationship between physical activity and the development of OA have attempted to quantify the amount of joint stress for individual types of activity. Selected types of physical activity transmit repetitive impact and torsional loads to the large weight-bearing joints such as the hip and knee, which may initiate and/or exacerbate cartilage degeneration [30]. The dose of joint stress is influenced by the type, frequency, duration, and intensity of physical activity as well as by gender, age, body weight, and the presence of joint injury. The aims of the present study were (1) to determine the influence of joint stress, frequency, intensity, and duration of physical activity on the risk of self-reported, physician-diagnosed hip/knee OA, (2) to assess the interaction between physical activity and known OA risk factors, and (3) to investigate whether a threshold of activity exists which may increase the risk of OA.