Influences of load carriage and physical activity history on tibia bone strain

Background:Military recruits are often afflicted with stress fractures.The military’s strenuous training programs involving load carriage may contribute to the high incidence of tibia stress fractures in the army.The purpose of this study was to assess the influences of incremented load carriage and history of physical activity on tibia bone strain and strain rate during walking.Methods:Twenty recreational basketball players and 20 recreational runners performed 4 walking tasks while carrying 0 kg,15 kg,25 kg,and35 kg loads,respectively.Tibia bone strain and strain rate were obtained through subject-specific multibody dynamic simulations and finite element analyses.Mixed model repeated-measures analyses of variance were conducted.Results:The mean±SE of the runners’ bone strain(μs)during load carriages(0 kg,15 kg,25 kg,and 35 kg)were 658.11±1.61,804.41±1.96,924.49±2.23,and 1011.15±2.71,respectively,in compression and 458.33±1.45,562.11±1.81,669.82±2.05,and 733.40±2.52,respectively,in tension.For the basketball players,the incremented load carriages resulted in compressive strain of 634.30±1.56,746.87±1.90,842.18±2.16,and 958.24±2.63,respectively,and tensile strain of 440.04±1.41,518.86±1.75,597.63±1.99,and 700.15±2.47,respectively.A dose-response relationship exists between incremented load carriage and bone strain and strain rate.A history of regular basketball activity could result in reduced bone strain and reduced strain rate.Conclusion:Load carriage is a risk factor for tibia stress fracture during basic training.Preventative exercise programs,such as basketball,that involved multidirectional mechanical loading to the tibia bones can be implemented for military recruits before basic training commences.

Energy expenditure and muscular activation patterns through active sitting on compliant surfaces

Purpose: To test the effectiveness of sitting surfaces with varied amounts of stability on muscle activity and energy expenditure.Methods: Using a within-participants repeated measures design, 11 healthy young-adult females(age = 20.0 ± 1.8 years) were measured using indirect calorimetry to assess energy expenditure, and electromyography to assess muscular activation in trunk and leg musculature under 3different sitting surfaces: flat-firm surface, air-filled cushion, and a stability ball. Data were analyzed using repeated measures analysis of variance with follow-up pairwise contrasts used to determine the specific effects of sitting surface on muscle activation and energy expenditure.Results: Significantly greater energy expenditure was recorded for the stability ball(p = 0.01) and the cushion(p = 0.03) over the flat surface(10.4% and 9.6% greater, respectively), with no differences between the ball and the cushion. Both the ball and the cushion produced higher tibialis anterior activation over the flat surface(1.09 and 0.63 root-mean-square millivolts(RMSmv), respectively), while the stability ball produced higher soleus activity over both cushion and flat surfaces(3.97 and 4.24 RMSmv, respectively). Additionally, the cushion elicited higher adductor longus activity over the ball and flat surfaces(1.76 and 1.81 RMSmv, respectively), but no trunk musculature differences were revealed.Conclusion: Compliant surfaces resulted in higher levels of muscular activation in the lower extremities facilitating increased caloric expenditure.Given the increasing trends in sedentary careers and the increases in obesity, this is an important finding to validate the merits of active sitting facilitating increased caloric expenditure and muscle activation.