Leg Extensor Power Research Articles

THE EFFECT OF 18 MONTH HIGH-IMPACT EXERCISE ON LOWER LIMB BONE MINERAL DENSITY IN PREMENOPAUSAL WOMEN 785

It was hypothesized that the rate of the mechanical strains developed in bone due to external loading is an important factor in the skeletal adaptive response to exercise. The purpose of this study was therefore to find out whether high-impact loading would affect beneficially the lower limb BMD in premenopausal women. A total of 98 clinically healthy and sedentary women volunteers (35-45 years) were randomly assigned to training (N=49) or control(N=49) group. The training consisted of supervised progressive high-impact exercises done an average 2.5 times/week for 18 months. The exercises were selected on the basis of a pilot study, which identified peak forces in 130 exercise movements. A total of 84 women completed the study (39 trainees and 45 controls). DXA measurements were made 3 times at 7 skeletal sites. Leg extensor power and the figure-of-8 running improved significantly (20% and-6%, respectively) as compared to control group (15% and -1%). The increases in the BMD at the loaded sites were 1.4 - 3.7% in the training group in contrast to changes of 0-1.8% in the control group. Intergroup differences of BMD are given in Table 1. This study showed that an 18 month high-impact training increased significantly the BMD of the loaded sites in premenopausal women. The results support the hypothesis that high strain rate loading of bones in versatile movements is potent in improving skeletal integrity.

Effects of Resistance Training on Strength, Power, and Selected Functional Abilities of Women Aged 75 and Older

To determine the effects of 12 weeks of progressive resistance strength training on the isometric strength, explosive power, and selected functional abilities of healthy women aged 75 and over. Subjects were matched for age and habitual physical activity and then randomly assigned into either a control or an exercise group. The Muscle Function Laboratory, Royal Free Hospital School of Medicine, London. Fifty-two healthy women were recruited through local and national newspapers. Five dropped out before and seven (4 exercisers and 3 controls) during the study. Pre- and posttraining measurements were obtained from 20 exercisers (median age 79.5, range 76 to 93 years) and 20 controls (median age 79.5, range 75 to 90 years). Training comprised one supervised session (1 hour) at the Medical School and two unsupervised home sessions (supported by an exercise tape and booklet) per week for 12 weeks. The training stimulus was three sets of four to eight repetitions of each exercise, using rice bags (1-1.5 kg) or elastic tubing for resistance. The exercises were intended specifically to strengthen the muscles considered relevant for the functional tasks, but were not to mimic the functional measurements. No intervention was prescribed for the controls. Pre- and posttraining measurements were made for isometric knee extensor strength (IKES), isometric elbow flexor strength (IEFS), handgrip strength (HGS), leg extensor power (LEP), and anthropometric indices (Body impedance analysis, arm muscle circumference, and body weight). Functional ability tests were chair rise, kneel rise, rise from lying on the floor, 118-m self-paced corridor walk, stair climbing, functional reach, stepping up, stepping down, and lifting weights onto a shelf. Pre- and posttraining comparisons were made using analysis of variance or analysis of covariance (using weight as a covariate) for normally distributed continuous data and one-sided Fishers exact test (2 x 2 table) for discontinuous data. Improvements in IKES (mean change 27%, P = .03), IEFS (22%, P = .05), HGS (4%, P = .05), LEP/kg (18%, P = .05) were associated with training, but the improvement in LEP (18%, P = .11) did not reach statistical significance. There was an association between training and a reduction in normal pace kneel rise time (median change 21%, P = .02) and a small improvement in step up height (median 5%, P = .005). The other functional tests did not improve. Progressive resistance exercise can produce substantial increases in muscle strength and in power standardized for body weight in healthy, very old women. However, isolated increases in strength and LEP/kg may confer only limited functional benefit in healthy, independent, very old women.

Weight-bearing exercise and ground reaction forces: A 12-month randomized controlled trial of effects on bone mineral density in healthy postmenopausal women

The effects of brief' daily exercise on bone mineral density (BMD) were assessed in a randomized controlled trial in 44 healthy postmenopausal women using weight-bearing exercise in a regimen adapted from osteogenic protocols reported in animal studies. BMD was assessed masked using dual energy X-ray absorptiometry at 0, 6, and 12 months. The sites assessed were the proximal femur (neck, Ward's triangle, and trochanter) and the lateral spine (L2–3) to assess the effects of the exercise, and the radius (ultradistal and 33% distal) as a marker for systemic effects. The test group was required to perform 50 “heel drops” daily at home (raising the body weight onto the toes and then letting it drop to the floor keeping the knees and hips extended) and to attend a weekly class of muted exercises, which included some high-impact activity. The control group also attended a weekly exercise class run by the same teacher, which included only low-impact activity, and did flexibility exercises at home daily. The ground reaction forces (as a ratio of body weight) during heel drops were 2.5 to 3.0 NN, with a rate of rise of 50–100 kN/sec. A patient with an instrumented femoral implant allowed comparison of compressive axial forces in the shaft of the proximal femur with the ground reaction forces, and these appeared to be transmitted undamped to the shaft of the femur. Initial analysis of BMD in the women showed no significant increases after 12 months of exercise at any site in either group, and the groups did not differ significantly from each other in this respect. Proximity to menopause was not associated with rapid bone loss, and in those who were more than 6 years postmenopausal, there was evidence for a maintenance effect of the exercise in the test group. Compliance (83%) and increases in leg extensor power (15%) were similar in both groups, and when they were combined, BMD was maintained at the trochanter but fell significantly at the radius ( p < 0.001).

Mobility after proximal femoral fracture: the relevance of leg extensor power, postural sway and other factors.

We studied 40 previously healthy women (median age 83 years 90% central range 77-90) 1 week after surgical fixation of their proximal femoral fracture to establish the significance of leg extensor power, postural sway, age, pre-injury mobility and fracture type in recovery of walking and stair-climbing ability. Subjects demonstrated a range of walking and stair-climbing abilities. Those not mobile all had sway greater than 40.9 cm/1 min and were more likely to have suffered a trochanteric fracture (p < 0.05). These subjects were not the oldest or those with the worst pre-injury mobility, but did report much greater pain (p < 0.05). Multiple linear regression revealed leg extensor power in the fractured leg (LEPf) to be the most important determinant of walking speed (R2 0.40, p < 0.001) and stair climbing time (R2 0.33, p < 0.002). LEPf was less than in the uninjured leg (p < 0.001), and accounted for only 30% of the total power output. LEPf was determined by pain, and not pre-injury mobility or fracture pattern. These findings have implications for the development of rehabilitation programmes.

Strength, power and related functional ability of healthy people aged 65-89 years.

This cross-sectional study was designed to examine the effects of healthy ageing on muscle strength, power, and potentially related functional ability. Subjects were recruited through local and national newspapers and inclusion was based on strict health criteria, by questionnaire. Isometric knee extensor, isometric elbow flexor and handgrip strength, leg extensor power, timed rise from a low chair, lifting a weighted bag on to a surface, and stepping unaided on to boxes of different heights were measured in 50 men and 50 women, evenly distributed over the age range 65-89 years. The differences in isometric strength and leg extensor power over the age range were equivalent to 'losses' of 1-2% per annum and approximately 3 1/2% per annum, respectively. The decline of explosive power was faster than the decline of knee extensor strength in men (p = 0.0001), but not significantly so in women (p = 0.08). Power standardized for body weight influenced chair rise time and step height. Isometric knee extensor strength standardized for body weight influenced chair rise time.

Effects of aerobic exercise conditioning at intensities corresponding to lactate threshold in the elderly.

In this study we attempted to determine the effects of exercise training at the intensity corresponding to lactate threshold (Thla-) on various health-related variables in sedentary but apparently healthy elderly subjects. Six men and five women volunteers [mean age 68.9 (SD 3.4) years] performed supervised endurance-type training on stationary cycle ergometers for 30 min and recreational activities for 30 min, 3 days a week for 12 weeks. Four men and four women served as the control group [68.8 (SD 4.4) years]. As a result of the training programme, statistically significant increases in maximal oxygen consumption (10%), oxygen consumption at Thla- (18%), distance covered in 12-min walk, side step, and leg extensor power were found in the training group, while no changes occurred in the control group. The changes in serum cholesterol and triglyceride concentrations from the pre- to post-training period were statistically significant. High-density lipoprotein cholesterol remained unchanged, and low-density lipoprotein cholesterol tended to decrease following the training programme. These data would indicate that exercise training at the intensity corresponding to Thla- may have favourable effects on overall physical fitness and some serum lipid variables in older individuals.

Leg extensor power and functional performance in very old men and women.

1. Residents of a chronic care hospital (13 men of mean age 88.5 +/- 6 SD years and 13 women of mean age 86.5 +/- 6 SD years) who had multiple pathologies were assessed for leg extensor capability in several ways. 2. A custom-built rig was used to assess leg extensor power, that is, maximal power output over less than 1 s in a single extension of one leg. Performance measures were obtained by timing chair rises (from a standard chair 0.43 m high), stair climbing (four risers, total height 0.635 m) and a walk (6.1 m). For each measurement the best of several trials were recorded as definitive. 3. Leg extensor power was significantly correlated with all performance measures, but the performance measures were not related to each other except for chair rising and walking speed. 4. Women had significantly less extensor power than men, but their power explained more of the variance in performance, e.g. power accounted for 86% of the variance in walking speed. 5. There was no relation within the group between age and any of the variables measured. 6. Measurement of leg extensor power in frail elderly people may prove useful in focusing effective rehabilitation programmes.

A new method for measuring power output in a single leg extension: feasibility, reliability and validity

A method is described for measuring the explosive power of the leg in extension which has been found safe and acceptable for all age groups and levels of physical capability. The extension movement takes 0.25-0.40 s in a push through 0.165 m against a flat pedal. At the end of the push the leg is fully extended. The movement is made seated so that the forces are contained between the buttocks and the foot. The seat position is adjusted for leg length and the push is transmitted by a lever and chain to spin a flywheel. The gearing is such that resistance to the movement remains velocity of the flywheel is measured by an optoswitch and used to calculated the average leg extensor power (LEP) in the push. The reliability of the power measurement was evaluated in 46 subjects ranging in age from 20 to 86 years; they included medical students and geriatric day patients. They were tested on two occasions separated by a week. The maximal values on the first occasion (best of at least five trials) ranged from 30 to 300 W (mean +/- 1 SD = 154 +/- 88 W). There was no significant difference on re-test and the coefficient of variation was 9.4%. In a subgroup of 9 non-naive subjects who were measured by an experienced observer it was 6.3%. As expected, power was lower in women than in men and declined sharply with age. The sex difference was less when the values were expressed as power per body mass; a sharp age-related decline remained.(ABSTRACT TRUNCATED AT 250 WORDS)