Effect of 6-month high-impact step aerobics and resistance training on BMD and tibial bending strength in sedentary premenopausal women.

The rationale of this study was to examine the effectiveness of 6-month high-impact step aerobics (SA) or moderate-intensity resistance training exercise (RT) on bone mineral density (BMD) and bone bending strength in sedentary women. Results show that SA enhanced BMD in the heel, lower leg, and lumbar spine 2. INTRODUCTION: To determine the effectiveness of 6 months of high-impact step aerobics (SA) or moderate-intensity resistance training (RT) on areal bone mineral density (aBMD) and tibial bending strength in sedentary premenopausal women. METHODS: Sixty-nine women (20-35 years old) who were randomly assigned to RT (n = 22), SA (n = 26), or non-treatment control (CON, n = 21) groups completed the study. SA had a minimum of 50 high-impact landings each training session. RT had a periodized lower body resistance training program incorporating eight exercises (65-85% of 1 repetition maximum: 1-RM). Both RT and SA met 3 times weekly. aBMD was assessed using dual X-ray absorptiometry (DXA). Tibial bending strength was assessed using mechanical response tissue analysis (MRTA). Measurements at 6 months were compared to baseline using ANCOVA, adjusted for baseline measures and covariates with α = 0.05. RESULTS: Calcaneus aBMD (0.0176 vs -0.0019 or -0.0009 g/cm2 relative to RT, p < 0.004, and CON, p < 0.006, respectively), lower leg aBMD (0.0105 vs -0.0036 g/cm2, relative to RT, p = 0.02), and lumbar spine 2 (L2) aBMD (0.0082 vs -0.0157 g/cm2 relative to CON, p < 0.02) were significantly greater in the SA group after 6 months. Tibial bending strength and bone resorption biomarkers were unchanged in all three groups after 6 months. CONCLUSION: Sedentary premenopausal women engaging in 6 months of high-impact aerobic exercise improved aBMD in the calcaneus, lower leg, and L2.

Stride parameters and hindlimb length in horses fatigued on a treadmill and at an endurance ride.

REASON FOR PERFORMING STUDY: The relationship between fatigue and stride and/or muscle stiffness requires further study. OBJECTIVE: To measure stride parameters in horses undergoing fatigue associated with running at submaximal speeds both on a treadmill and in an endurance ride. HYPOTHESIS: Stride frequencies and estimates of hindlimb stiffness would be decreased in fatigued horses. METHODS: Horses were fatigued using 2 paradigms: run to exhaustion at a treadmill (4.5 m/sec, 6% incline) and finishing an 80 km endurance ride. Videos were digitised before and after fatigue and analysed for stride parameters: hind limb length, stride frequency, time of contact, step length, duty factor and stride length. RESULTS: In fatigued horses, stride durations were 5% longer (P = 0.007) resulting in lower stride frequencies (P = 0.016) and longer stride lengths (P = 0.006). The time of contacts (tc) for stance phase were not different (P = 0.108) nor was duty factor (tc/stride period, P = 0.457). Step length (speed x tc) and hindlimb lengths were also not different (P = 0.104, P = 0.8). For endurance horses, stride data for nonfatigued horses were consistent with data extrapolated to 4.5 m/sec from nonfatigued horses on the treadmill. Endurance horses slowed (P = 0.002) during the race from 4.55 to 4.03 m/sec and stride lengths were shorter. Despite a slower speed, other stride parameters were unchanged. Hindlimb length was shorter in fatigued horses. CONCLUSION: Horses fatigued on a treadmill and during the natural course of an endurance ride responded differently, biomechanically. On the treadmill, where speed is constrained, stride frequencies decreased and stride lengths increased. During one endurance ride, stride frequencies were the same, although speeds were substantially reduced. Limb length was shorter in fatigued endurance horses. It remains to be determined if these changes in mechanics are advantageous or disadvantageous in terms of energetics or injury. Further examination of endurance rides is also warranted.