High impact exercise increased femoral neck bone mineral density in older men: A randomised unilateral intervention

Abstract

Introduction

There is little evidence as to whether exercise can increase BMD in older men with no investigation of high impact exercise. Lifestyle changes and individual variability may confound exercise trials but can be minimised using a within-subject unilateral design (exercise leg [EL] vs. control leg [CL]) that has high statistical power.

Purpose

This study investigated the influence of a 12 month high impact unilateral exercise intervention on femoral neck BMD in older men.

Methods

Fifty, healthy, community-dwelling older men commenced a 12 month high impact unilateral exercise intervention which increased to 50 multidirectional hops, 7 days a week on one randomly allocated leg. BMD of both femurs was measured using dual energy X-ray absorptiometry (DXA) before and after 12 months of exercise, by an observer blind to the leg allocation. Repeated measures ANOVA with post hoc tests was used to detect significant effects of time, leg and interaction.

Results

Thirty-five men (mean ± SD, age 69.9 ± 4.0 years) exercised for 12 months and intervention adherence was 90.5 ± 9.1% (304 ± 31 sessions completed out of 336 prescribed sessions). Fourteen men did not complete the 12 month exercise intervention due to: health problems or injuries unrelated to the intervention (n = 9), time commitments (n = 2), or discomfort during exercise (n = 3), whilst BMD data were missing for one man. Femoral neck BMD, BMC and cross-sectional area all increased in the EL (+ 0.7, + 0.9 and + 1.2 % respectively) compared to the CL (− 0.9, − 0.4 and − 1.2%); interaction effect P < 0.05. Although the interaction term was not significant (P > 0.05), there were significant main effects of time for section modulus (P = 0.044) and minimum neck width (P = 0.006). Section modulus increased significantly in the EL (P = 0.016) but not in the CL (P = 0.465); mean change + 2.3% and + 0.7% respectively, whereas minimum neck width increased significantly in the CL (P = 0.004) but not in the EL (P = 0.166); mean changes being + 0.7% and + 0.3% respectively.

Conclusion

A 12 month high impact unilateral exercise intervention was feasible and effective for improving femoral neck BMD, BMC and geometry in older men. Carefully targeted high impact exercises may be suitable for incorporation into exercise interventions aimed at preventing fractures in healthy community-dwelling older men.

Introduction

Osteoporotic fractures are a major public health problem amongst older adults. One in two women and one in five men aged fifty and over in the UK will suffer a fracture in their lifetime [1]. Osteoporotic fractures commonly occur at the hip, spine, and wrist and of these hip fractures have the highest short-term mortality, morbidity and associated socio-economic impact [2], [3], [4]. Regular exercise is widely recommended as the most effective non-pharmacological method for improving and maintaining BMD [5] and can also reduce the risk of falling. As such, exercise has an important role in reducing the predisposition to osteoporotic hip fracture.

Although older people are the population at most immediate risk of osteoporosis, it has been suggested that exercise may be less effective in older, than younger, people [6], [7]. This may be related to the type and intensity of the exercise interventions studied, as lower neuromuscular function [8] or greater injury risk may limit exercise intensity in older people. Meta analysis of exercise intervention studies suggests that mixed loading interventions including low to moderate impact exercises in the form of jogging, walking and stair climbing, together with resistance training, can maintain BMD at the femoral neck in postmenopausal women [9]. However, evidence from animal experiments suggests that the optimal loading regimens are high in magnitude, high in strain rate and provide novel stress on the bone [10], [11], [12], [13]. In children and young adults, high impact jumping exercises that exert a high magnitude of loading at the hip have produced the greatest increases in femoral neck BMD [6]. Therefore, interventions that incorporate brief but regular high impact exercise could potentially increase femoral neck BMD (rather than just preventing bone loss) in older adults.

Few studies have investigated the effects of interventions consisting only of high impact loading in the form of vertical jumping on femoral neck BMD in older people [14], [15]. These studies found no change in femoral neck BMD following the intervention but these findings pertain to postmenopausal women, whose adaptive response to mechanical loading is thought to be impaired by estrogen deficiency and reduced estrogen receptor number [16], [17].

Older men are at risk of osteoporotic fractures, and hip fracture related morbidity and mortality are higher for men than women [18]. However, there is little information concerning the effects of long-term exercise interventions on BMD in this population [19], [20]. One exercise intervention including high impact exercises (single and double foot landings, bench stepping, and jumping off 15- and 30-cm benches) increased femoral neck BMD in middle aged and older men (50–79 years) [21], [22]. However, the high impact exercises in this intervention formed only a very small component of a progressive resistance training programme, requiring over 3 h of exercise per week. High impact exercise alone may be more feasible, as exercises are less time-consuming and can be performed at home, without requiring any special equipment. Brief, high impact exercises performed at home can increase BMD in premenopausal women [23], but the effectiveness of high impact exercise alone on femoral neck BMD in older men is unknown.

Individual differences and lifestyle modifications such as genotype, physical activity, diet and age-related change may confound longitudinal exercise intervention trials in older people [24]. The effect of these confounders can be minimised by using a within-subjects unilateral design (exercise leg [EL] vs. control leg [CL]) that has greater statistical power than studies comparing changes between individuals. Recently, it was demonstrated that high impact unilateral exercise increases femoral neck BMD in premenopausal women [25]. Therefore, the aim of this study was to investigate the influence of a 12 month high impact unilateral exercise intervention on femoral neck BMD in healthy community dwelling older men, using a within-subjects unilateral design.