Relationship Between Thigh Muscle Strength, Competitive Exercise, and BMD in Elderly Athletes and Controls

Abstract

PURPOSE: This study investigated the relationship between competitive exercise, quadriceps and hamstring strength and regional and total body bone mineral density (BMD) in elite senior athletes and healthy elderly controls. METHODS: The 183 participants included 104 athletes of the National Senior Games (72.6±6.4 yrs, 72.6±13.5 kg, 168.7±8.6 cm) and 79 healthy controls (75.4±5.6 yrs, 79.5±11.7 kg, 170.8±25.5 cm). Three 5-sec trials of isometric knee flexion and extension were collected (100 Hz) using a load-cell affixed to a custom apparatus which held the knee at 45 degrees. Hip, radius, spine, and total body BMD were measured with a Hologic 4500A DXA scanner. For each of the 4 BMD sites assessed, multiple linear regression analysis was performed in four steps (α = 0.10). First, age, gender, and bodyweight were entered as a block into the statistical model to determine their correlation with the BMD variable. Secondly, group (athlete, control) was added. Subsequently, extension flexion peak torque was entered into the model. Lastly, because extension and flexion peak torque are highly correlated (R=0.67), extension peak torque was removed and flexion peak torque was added to the model. RESULTS: The variables of gender, age, and bodyweight explained 26%, 52%, 24%, and 33% of the variance in hip, radius, spine, and total body BMD, respectively. The inclusion of the group variable did not add significantly to any the model. The addition of extension peak torque into the model resulted in an increase of explained variance of 1.5% in hip BMD (p = 0.07). It was not related to BMD at any other site. Flexion peak was not related to BMD at any of the sites measured. CONCLUSIONS: Age, gender, and body weight were predictive of BMD at the hip, radius, spine, and in the total body. Highly competitive exercise was not related to BMD. Hip BMD was correlated with quadriceps strength after controlling for the effects of competitive exercise, gender, age, and bodyweight.