Abstract
BackgroundTreadmill animal models are commonly used to study effects of exercise on bone. Since mechanical loading induces bone strain, resulting in bone formation, exercise that induces higher strains is likely to cause more bone formation. Our aim was to investigate the effect of slope and additional load on limb bone strain.MethodsHorizontal and vertical ground reaction forces on left fore-limb (FL) and hind-limb (HL) of twenty 23-week old female Wistar rats (weight 279 ± 26 g) were measured for six combinations of SLOPE (−10°, 0°, +10°) and LOAD (0 to 23% of body mass). Peak force (Fmax), rate of force rise (RC), stance time (Tstance) and impulse (Fint) on FLs and HLs were analyzed.ResultsFor the FL, peak ground reaction forces and rate of force rise were highest when walking downward −10° with load (Fmax = 2.09±0.05 N, FLRC = 34±2 N/s) For the HL, ground reaction forces and rate of force rise were highest when walking upward +10°, without load (Fmax = 2.20±0.05 N, HLRC = 34±1 N/s). Load increased stance time. Without additional load, estimates for the highest FL loading (slope is −10°) were larger than for the highest HL loading (slope is +10°) relative to level walking.ConclusionsThus, walking downward has a higher impact on FL bones, while walking upward is a more optimal HL exercise. Additional load may have a small effect on FL loading.
Highlights
Treadmill animal models are commonly used to study effects of exercise on bone
We aimed to study the effects of additional load on ground reaction forces of rat fore limbs (FL) and hind limbs (HL)
With additional load the rat walked with a concave back
Summary
Treadmill animal models are commonly used to study effects of exercise on bone. Since mechanical loading induces bone strain, resulting in bone formation, exercise that induces higher strains is likely to cause more bone formation. The physiological mechanisms that underlie bone mechano-responsiveness are usually studied in animal models, especially in rats, for which different types of non-invasive exercise interventions have been developed. These interventions include voluntary wheel (Aikawa et al 2015; Fonseca et al 2011), treadmill running (Bennell et al 2002; Chen et al 1994; Chen et al 2011; Clarke 1995), treadmill running with additional load (Tromp et al 2006; Bravenboer et al 2001; Van der Wiel et al 1995), climbing (Mori et al 2003), jumping (Honda et al 2003), and weight lifting (Wirth et al 2003).
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