Enhanced Daily Load Stimulus to Bone in Spaceflight and on Earth

British Journal of Sports Medicine, 2006

Step exercise has been promoted as a low impact physical activity recommended for the improvement of cardiorespiratory and muscular fitness. This recreational activity might also be recommended to improve bone health since mechanical load plays an important role in the normal development of the skeleton. Methods: Our main purpose was to characterised 100 step sessions and to calculated osteogenic index (OI) according to Turner and Robling: OI (one session) = peak ground reaction force(BW)*ln(number of loading cycles+1). Results: Main results (mean¡SD) were as follows: OI was 12.0¡0.8; peak ground reaction force (GRF) was 1.40¡0.10 times body weight (BW); session duration was 38.6¡8.3 min; stepping rate was 134.6¡4.7 beats per minute (bpm); the movements performed most often were marching, knee hop, side leg, L step, and over the top; and the number of loading cycles was 4194.1¡1055.2. OI and GRF increased significantly when stepping rate was higher than 135 bpm. This stepping rate might be used as a reference for higher intensity classes. A frequency of two to three sessions per week of step exercise is recommended. Conclusions: Despite the benefits that have been stated when step classes are structured correctly and adapted to the participants, further research is needed concerning biomechanical load, exercise prescription, and injury prevention.

Bone, 2011

This study tests Wolff's law of trabecular bone adaptation by examining if induced changes in joint loading orientation cause corresponding adjustments in trabecular orientation. Two groups of sheep were exercised at a trot, 15 min/day for 34 days on an inclined (7°) or level (0°) treadmills. Incline trotting caused the sheep to extend their tarsal joints by 3-4.5°during peak loading (P b 0.01) but has no effect on carpal joint angle (P = 0.984). Additionally, tarsal joint angle in the incline group sheep were maintained more extended throughout the day using elevated platform shoes on their forelimbs. A third "sedentary group" group did not run but wore platform shoes throughout the day. As predicted by Wolff's law, trabecular orientation in the distal tibia (tarsal joint) were more obtuse by 2.7 to 4.3°in the incline group compared to the level group; trabecular orientation was not significantly different in the sedentary and level groups. In addition, trabecular orientations in the distal radius (carpal joint) of the sedentary, level and incline groups did not differ between groups, and were aligned almost parallel to the radius long axis, corresponding to the almost straight carpal joint angle at peak loading. Measurements of other trabecular bone parameters revealed additional responses to loading, including significantly higher bone volume fraction (BV/TV), Trabecular number (Tb.N) and trabecular thickness (Tb.Th), lower trabecular spacing (Tb.Sp), and less rod-shaped trabeculae (higher structure model index, SMI) in the exercised than sedentary sheep. Overall, these results demonstrate that trabecular bone dynamically adjusts and realigns itself in very precise relation to changes in peak loading direction, indicating that Wolff's law is not only accurate but also highly sensitive.

A newly developed bone-specific physical activity questionnaire (BPAQ) was compared with other common measures of physical activity for its ability to predict parameters of bone strength in healthy, young adults. The BPAQ predicted indices of bone strength at clinically relevant sites in both men and women, while other measures did not. Introduction Only certain types of physical activity (PA) are notably osteogenic. Most methods to quantify levels of PA fail to account for bone relevant loading. Our aim was to examine the ability of several methods of PA assessment and a new bone-specific measure to predict parameters of bone strength in healthy adults. Methods We recruited 40 men and women (mean age 24.5). Subjects completed the modifiable activity questionnaire, Bouchard 3-day activity record, a recently published bone loading history questionnaire (BLHQ), and wore a pedometer for 14 days. We also administered our bone-specific physical activity questionnaire (BPAQ). Calcaneal broadband ultrasound attenuation (BUA) (QUS-2, Quidel) and densitometric measures (XR-36, Norland) were examined. Multiple regression and correlation analyses were performed on the data. Results The current activity component of BPAQ was a significant predictor of variance in femoral neck bone mineral density (BMD), lumbar spine BMD, and whole body BMD (R 2 =0.36-0.68, p<0.01) for men, while the past activity component of BPAQ predicted calcaneal BUA (R 2 =0.48, p=0.001) for women. Conclusions The BPAQ predicted indices of bone strength at skeletal sites at risk of osteoporotic fracture while other PA measurement tools did not.

The purpose of this study was to determine how unweighted running on a lower body positive pressure treadmill (LBPPT) modifies in-shoe regional loading. Ten experienced runners were fit with pressure distribution measurement insoles and ran at 100%, 120%, and 140% of self-reported easy training pace on a LBPPT at 20%, 40%, 60%, 80%, and 100% body weight percentage settings (BW Set). Speeds and BW Set were in random order. A linear mixed effect model (po0.05 significance level) was used to compare differences in whole foot and regional maximum in-shoe plantar force (F MAX), impulse, and relative load distribution across speeds and BW Set. There were significant main effects (po 0.001) for running speed and BW Set for whole foot F max and impulse. The model revealed 1.4% and 0.24% increases in whole foot F MAX (times body weight) and impulse, respectively, for every unit increase in body weight percentage. There was a significant main effect for BW Set on F max and relative load (p o0.05) for each of the nine foot regions examined, though four regions were not different between 80% and 100% BW Set. There was a significant (po 0.001) main effect for BW Set on forefoot to rear foot relative load. Linear relationships were found between increases in BW Set and increases in-shoe F max and impulse, resulting from regional changes in foot pressure which represent a shift towards forefoot loading, most evident o 80% BW Set. Estimating in-shoe regional loading parameters may be useful during rehabilitation and training to appropriately prescribe specific speed and body weight levels, without exceeding certain critical peak force levels while running.

Perttunen, Jarmo Finnish summary Diss.

Journal of Experimental Zoology Part A: Ecological Genetics and Physiology, 2010

Understanding the relationship between external load and bone morphology is critical for understanding adaptations to load in extant animals and inferring behavior in extinct forms. Yet, the relationship between bony anatomy and load is poorly understood, with empirical studies often producing conflicting results. It is widely assumed in many ecological and paleontological studies that bone size and strength reflect the forces experienced by the bone in vivo. This study examines that assumption by providing preliminary data on gait mechanics in a hypermuscular myostatindeficient mouse model with highly mineralized and hypertrophied long bones. A small sample of hypermuscular and wild-type mice was video recorded while walking freely across a force platform. Temporal gait parameters, peak vertical and transverse (mediolateral) ground reaction forces (GRFs), vertical impulse, and loading rates were measured. The only gait parameters that differed between the two groups were the speeds at which the animals traveled and the transverse forces on the hind limb. The myostatin-deficient mice move relatively slowly and experienced the same magnitude of vertical forces on all limbs and transverse forces on the forelimb as the wildtype mice; though the myostatin-deficient mice did experience lower mediolateral forces on their hindlimbs compared with the wild-type mice. These preliminary results call into question the hypothesis that skeletal hypertrophy observed in hypermuscular mice is a result of larger GRFs experienced by the animals' limbs during locomotion. This calls for further analysis and a cautious approach to inferences about locomotor behavior derived from bony morphology in extant and fossil species.

Journal of Rehabilitation Research and Development, 2009

Low bone mineral density (BMD) and osteoporosis are health concerns among older adults and individuals with physical, neurological, and/or mobility impairments. Detrimental changes in bone density and bone architecture occurring in these individuals may be due in part to the reduction/cessation of physical activity and the accompanying reduction of mechanical strain on bone. Changes in bone architecture predispose these individuals to fragility fractures during low-trauma events. Whole-body vibration (WBV) has been examined as an intervention for maintaining or improving bone mass among people with low BMD, because it may emulate the mechanical strains observed during normal daily activities. This article provides an overview of WBV including terminology, safety considerations, and a summary of the current literature; it is intended for rehabilitation healthcare providers considering WBV as a potential therapy for individuals with osteoporosis.

Bone, 2007

Introduction: Mechanical stresses on the bone are an important aspect of physical activity that promotes bone preservation and increases in bone mass. Exercise intensities leading to bone preservation and accrual have not been adequately defined for humans in general, and postmenopausal women in particular. Materials and methods: To quantify parameters of effective walking intensity for preservation and accrual of bone mineral, healthy postmenopausal women engaged in 30 weeks of supervised walking, 4.8 km per day, 4 days a week at intensities of 102% or 123% of the ventilatory threshold (VT) equivalent to 67% and 86% of maximal effort (VO 2 max). Subjects were matched by age, body mass, hormone replacement status (HRT) and VT. Areal bone mineral density (aBMD) determined by DXA (n = 25) and bone formation markers osteocalcin (OC), and bone-specific alkaline phosphatase (bALP) (n = 43), were measured at the outset and at 15-week intervals. Peak vertical forces at corresponding intensities were measured (n = 9) on a force plate. Results: aBMD of legs and whole body, but not of other sites, and lean mass of legs, but not of arms, increased after 15 weeks of high intensity, compared to moderate losses for low intensity training. Leg and total body aBMD was preserved and slightly increased with loads greater than 872.3 newtons (N) with a walking intensity above 115% of VT or 74% of VO 2 max, speeds above 6.14 km/h, and heart rates above 82.3% of agespecific maximum. OC and bALP did not correlate with training-induced changes in aBMD. Conclusions: At exercise intensities above 115% of VT or 74% of VO 2 max, and walking speeds above 6.14 km/h, mechanical loading of 872.3 N or 1.22 times body weight is sufficient for increases in leg muscle mass and preservation of BMD in postmenopausal women.

2013

Mechanical stimuli influence bone strength, with internal muscular forces thought to be the greatest stressors of bone. Consequently, the effects of exercise in improving and maintaining bone strength have been explored in a number of interventional studies. These studies demonstrate a positive effect of high-impact activities (i.e. where large muscle forces are produced) on bone strength, with benefits being most pronounced in interventions in early pubertal children. However, current studies have not investigated the forces acting on bones and subsequent deformation, preventing the development of optimised and targeted exercise interventions. Similarly, the effects of number and frequency of exercise repetitions and training sessions on bone accrual are unexplored. There are conflicting results as to gender effects on bone response to exercise, and the effects of age and starting age on the osteogenic effects of exercise are not well known. It also appears that exercise interventions are most effective in physically inactive people or counteracting conditions of disuse such as bed rest. Bone strength is only one component of fracture risk, and it may be that exercise resulting in improvements in, e.g., muscle force/power and/or balance is more effective than those whose effects are solely osteogenic. In summary, exercise is likely to be an effective tool in maintaining bone strength but current interventions are far from optimal.

Journal of Orthopaedic Research, 2007

High-frequency whole body vibrations can be osteogenic, but their efficacy appears limited to skeletal segments that are weight bearing and thus subject to the induced load. To determine the anabolic component of this signal, we investigated whether low-level oscillatory displacements, in the absence of weight bearing, are anabolic to skeletal tissue. A loading apparatus, developed to shake specific segments of the murine skeleton without the direct application of deformations to the tissue, was used to subject the left tibia of eight anesthesized adult female C57BL/6J mice to small (0.3 g or 0.6 g) 45 Hz sinusoidal accelerations for 10 min/day, while the right tibia served as an internal control. Video and strain analysis revealed that motions of the apparatus and tibia were well coupled, inducing dynamic cortical deformations of less than three microstrain. After 3 weeks, trabecular metaphyseal bone formation rates and the percentage of mineralizing surfaces (MS/BS) were 88% and 64% greater (p < 0.05) in tibiae accelerated at 0.3 g than in their contralateral controls. At 0.6 g, bone formation rates and mineral apposition rates were 66% and 22% greater (p < 0.05) in accelerated tibiae. Changes in bone morphology were evident only in the epiphysis, where stimulated tibiae displayed significantly greater cortical area (þ8%) and thickness (þ8%). These results suggest that tiny acceleratory motions -independent of direct loading of the matrix -can influence bone formation and bone morphology. If confirmed by clinical studies, the unique nature of the signal may ultimately facilitate the stimulation of skeletal regions that are prone to osteoporosis even in patients that are suffering from confinement to wheelchairs, bed rest, or space travel. ß