This research examines a question about which is worse to the knee joint: increasing body weight or decreasing muscle force. We simulated unilateral weight bearing and analyzed the extent to which each had a deleterious effect on the knee joint. We used a rigid body model in which body weight was increased and quadriceps muscle force decreased. Also, to account for differences between men and women, the model reflected difference in pelvic width. In this simulation, decreasing muscle strength by 30% of its initial normal value had a stronger unfavorable effect than that of increasing body weight to the same relative degree. The effect of differences in body proportion between men and women did not appreciably influence the results, as long as masses and linear dimensions were average values of the respective sexes. Our results suggest that a patient with osteoarthritis in the knee should pay particular attention to problems of muscle weakness.
Past intervention studies on bone remodeling for preventing osteoporosis in elderly women often lack sufficient description of the intensity of the exercise, though bone remodeling is dependent on applied force at specific sites. The effectiveness of exercise in increasing bone density cannot be defined without sufficient description of the intensity and targeted site of the exercise. We conducted kinetic and kinematic analyses of the lower extremities in order to categorize exercise in terms of compression force applied at the proximal end of the femur, to formulate guidelines for prescribing exercise to elderly women. Thirty healthy women aged 18-24 participated in the study. Joint compression force at the proximal end of the femur was measured with the aid of motion analysis devices under several conditions of impulsive loading. Joint compression force at the proximal end of the femur was estimated for twenty-two exercise regimes varying from low to high-impact exercises, including jumping off, stepping down, vertical jumping, and dropping down after heel raises. Some exercises appear to be inappropriate for exercise intervention, because the variability for these exercises is high. Most of the jumping exercises, with coefficients exceeding 0.36, were excluded from further analysis. Of the remaining exercises, four were categorized as statistically different loads, as determined by a posthoc test of one-way analysis of variance of joint compression force. These included jumping off a 10 cm platform, stepping down from a 20 cm platform with the knees in the extended position, stepping down from a 20 cm platform with the knees in a relaxed position, and heel dropping at 80 cycles per minute with the knees in a relaxed position. The joint compression forces during these exercises were 2.32 ± .81, 1.81 ± .59, 1.45 ± .59, and 1.00 ± .27 times as much as the subject’s body weight, respectively.
This study investigates the effects of Ca on bone in the ovariectomized mice. Twenty-six female ICR mice aged 5 weeks were used. They were ovariectomized (OVX) or sham-operated (SHAM) and fed standard mouse diet (SF) or special low calcium diet (L.Ca), respectively. All animals were sacrificed at day 100 after operation. Mechanical strength of the left femur and tibia was measured by the three-point bending strength test. The bones were dried, weighed and burned to ash. Correlation between mechanical strength and ash content was found. A specimen of the right tibia was prepared. Mechanical strength, ash content and ratio of dry bone weight to body weight of the femur and tibia in OVX and L.Ca mice were significantly less than in SHAM and SF mice. SHAM/SF mice and OVX/L.Ca group showed highest and lowest values in all cases. The values for the femur and tibia in OVX/SF mice were lower than in SHAM/SF group and in OVX/L.Ca group were less than in OVX/SF mice. Correlation coefficients for mechanical strength and ash content were 0.704 and 0.776 for the femur and tibia. Ca is thus related to inhibition of bone loss and maintenance of bone mass and effective prevention of osteoporosis.
Changing of standing position and visual blocking methods have been used as a convenient evaluation of standing balance by physical therapists. The purpose of this study was to investigate the effects of changes of foot positions on Romberg’s quotient of postural sway and the tibialis anterior and gastrocnemius muscles activities in standing for normal men. Subjects were 45 college students. For the measurement of muscles activities, 15 subjects were selected at random from among the 45 students. The standing positions were standing with legs 10 cm apart, standing with legs together, tandem standing, standing on tiptoes, and standing on one leg with the eyes open and closed. Measurements were made using a center of foot pressure recorder and surface electromyography for 30 seconds. Romberg’s quotient and the relative muscle activities of the leg were both found to be in the order standing with legs apart, standing with legs together, tandem standing, standing on tiptoes, standing on one leg. It has conventionally been considered that the instability of postural sway is increased when vision is blocked. The present results suggested that postural regulation by the physiological subsystem is indirectly affected by vision and somatosensory input.
The purpose of this study was to clarify the effect of changing footwear conditions on postural response against postural perturbation. Twenty-three healthy subjects participated in this study. Postural response was induced by moving a platform forward, hereafter referred to as forward-perturbation of a platform. The center of pressure (COP) from the force plate and the electromyograms (EMG) of the tibialis anterior (TA) and quadriceps femoris (QUAD), which are both agonists of the response, were measured. The effect of plantar material and shape of footwear on postural response was examined as footwear condition. Changing plantar materials had an effect on integrated EMG of the agonists (IEMG) but not on the response pattern. On the other hand, the shape of footwear had an effect on the response pattern but not on IEMG. It was supposed from this result that changes in somatosensory input, caused by coupling of plantar material and shape of footwear, modifies postural response variously.
This study was conducted to investigate the effects of stride walking on cardiovascular and electromyographical responses on a treadmill in healthy young female (mean age of 23.0 yrs, height of 156.2 cm and weight of 50.6 kg). The subjects performed initial 6 minutes walking based on a heart rate of anaerobic threshold minus 10 beats per minute under two conditions of treadmill walking, on increased velocity with horizontal inclination (A) and on a constant velocity (2.0 mph) with increased grade (B). Consequently, the subjects performed stride walking which was made by 10% reduction of steps under each condition. The results were as follows: 1) Under A condition, the values of leg fatigue by Borg’s 20 numeric scale in stride walking was significantly higher than in non-stride walking, while no difference under B condition. 2) Under A condition, the mean values in oxygen uptake and heart rate during stride walking were significantly higher than during non-stride walking, while no difference under B condition. 3) Under A condition, total amount of integrated electromyogram in gastrocnemius, vastus medialis and tibialis anterior were higher during stride walking than during non-stride walking. Under B condition, gastrocnemius and gluteus maximus showed higher values during stride walking than in non-stride walking. These findings suggest that stride walking manipulated on a high velocity tends to alter cardiovascular and electromyographical parameters than on a lower velocity with higher inclination on treadmill walking in healthy young adults.