Inter-arm asymmetry in bone mineral content and bone area in postmenopausal recreational tennis players

Abstract

Objective: To determine whether long-term recreational tennis participation is associated with increased bone and muscle mass in the dominant compared to the non-dominant arm, in postmenopausal tennis players. Methods: Dual-energy X-ray whole body scans were performed in 10 postmenopausal tennis players (mean±S.D.; 59.7±4.8 years) and 12 postmenopausal non-active women (62.8±7.2 years) matched for age and height. Tennis players started in this sport at 31.4±8.8 years, and had been playing for 26.8±6.8 years, at least 3 h per week. In addition, shoulder isokinetic muscular strength was also evaluated. Results: Tennis participation resulted in a lower whole mass and fat mass in both arms (P<0.05). Dominant arm muscle mass and shoulder joint isokinetic strength were essentially similar in both groups, however, the tennis players showed 8% greater bone mineral content and 7% greater osseous area in the dominant than in the non-dominant arm (P<0.05). No inter-arm differences were found in bone mineral density. A relationship was observed between the length of tennis participation and the degree of inter-arm asymmetry in bone mineral content (r=0.81, P<0.01) and bone area (r=0.78, P<0.01). However, the BMD of the arms was essentially similar in both groups. No differences were observed in femoral and lumbar bone mass and density between groups. Conclusions: Long-term tennis participation is associated with increased bone mass, but not BMD, in the dominant arm of postmenopausal tennis players. The magnitude of the inter-arm asymmetry of postmenopausal tennis players is proportional to the length of tennis participation.

Introduction

Weight-bearing exercise is advised to maximise peak bone mass during growth and to attenuate the loss of bone mass, bone mineral density (BMD) and skeletal muscle mass with ageing [1], [2], [3], which may lead to osteoporosis [4], [5] and sarcopenia [6], [7], [8]. The loss of muscle and bone mass is markedly accentuated after menopause in women [4], [5], [6]. Osteoporosis impairs bone mechanical competency increasing the risk of bone fractures [9]. In addition, sarcopenic elders have reduced muscle strength and are not able to counteract so efficiently as young people unbalancing forces such that, sarcopenic individuals are at a higher risk of suffering drops and bone fractures [10]. In adolescents and young adults regular physical activity has anabolic effects on loaded bones and muscles, which oppose to the catabolic effect of inactivity [1], [11], [12], [13]. In contrast, the anabolic effect of physical activity on bones and skeletal muscles appears to be reduced after the menopause [11], [14]. The rate and magnitude of bone loss may markedly differ from one skeletal site to another, depending, among other factors, on local mechanical stress. Several randomised trials of the effect of exercise on bone mass in postmenopausal women have shown that participation in intense impact and weight bearing exercise programs attenuates postmenopausal bone loss at the lumbar spine and femoral neck [2], [3]. However, it remains to be determined if recreational physical activities, such as tennis participation, may effectively delay the development of osteoporosis and sarcopenia in postmenopausal women. Based on the results obtained with young adults it has been suggested that tennis may be an appropriate sport to maintain and increase bone mass in clinically relevant regions [12], [15], [16], [17]. This possibility may be tested by determining femoral and lumbar bone mineral content (BMC) and BMD in postmenopausal tennis players and age-, weight- and height-matched control subjects from the same population.

Despite BMC and BMD being mainly genetically determined [18], other factors, in addition to mechanical loading, such as nutritional, hormonal, and exposure to drugs and toxins may also affect bone metabolism. Genetic and environmental factors may be controlled for by studying side-to-side differences in unilateral models of mechanical loading, as previously reported in tennis players [12], [15], [16], [17]. However, the majority of previous studies were carried out in young or middle-aged tennis players, who started tennis participation at prepubertal ages or 1 or more years after the menarche, when bones are more sensitive to mechanical stimulation [16]. Less is known about the long-term effects of exercise on bone tissue, especially when started in adult life. Particularly, there is lack of evidence whether there is any bone benefit in postmenopausal players who had been playing recreationally since adulthood.

Therefore, the aim of this study was to evaluate whether long-term recreational tennis participation is associated with increased bone mass and density in clinically relevant regions, such as the hip and the lumbar spine. Additionally we aimed at determining the responsiveness of potstmenopausal bone to mechanical overloading by studying the dominant to non-dominant arm differences in bone mass, bone density, bone area, muscle mass and muscle strength in postmenopausal tennis players who begun their participation in tennis at adult ages. Since this model of exercise accounts for most of genetic and environmental confounding factors, a lack of muscle and bone mass enhancement in the loaded arm compared to the contralateral arm would suggest that the responsiveness of bone and muscle to mechanical stimuli is attenuated in postmenopausal women.