Design and validation of a knee brace with feedback to reduce the rate of loading.

The repetitive nature of walking can lead to repetitive stress and associated complications due to the rate of loading (ROL) experienced by the body at the initial contact of the foot with the ground. An individual's gait kinematics at initial contact has been suggested to give rise to the ROL, and a repetitive, high ROL may lead to several disorders, including osteoarthritis. We present the design, development, and validation of a knee brace that provides feedback to the user during gait. The feedback consists of an auditory signal when the specific parameters of knee angle or tibial acceleration 50 ms prior to contact are exceeded. Nine women were recruited for the gait analysis, and the gait characteristics with and without the brace and feedback are analyzed. Our results indicate that using a knee brace with feedback can effectively change the gait kinematics used during walking, leading to a reduced ROL experienced at initial contact. Using a knee brace with feedback is a novel approach to gait retraining. Al-though the kinetics of how the subjects change in gait pattern is unknown, the reduced ROL experienced is significant and warrants further investigation.

Proprioception, gait kinematics, and rate of loading during walking: are they related?

The cyclic nature of walking can lead to repetitive stress and associated complications due to the rate of loading (ROL) experienced by the body at the initial contact of the foot with the ground. An individual's gait kinematics at initial contact has been suggested to give rise to the ROL, and a repetitive, high ROL may lead to several disorders, including osteoarthritis. Additionally, proprioception, the feedback signaling of limb position and movement, may play a role in how the foot strikes the ground and thus, the ROL. Our goal was to explore the relationship between proprioception, gait kinematics and ROL. Thirty-eight women were recruited for gait analysis, and the gait characteristics 50 ms prior to and at initial contact were examined. Two proprioception tests, joint angle reproduction and threshold to detect passive motion were used to examine the subject's proprioceptive acuity. Our results indicate that individuals with a larger knee angle (i.e., greater extension) 50 ms prior to initial contact (IC) experience a higher ROL during gait and have poorer proprioceptive scores. However, it remains unclear whether poor proprioception causes a high ROL or if a high ROL damages the mechanoreceptors involved in proprioception, but the apparent relationship is significant and warrants further investigation.

Effects of physical training on proprioception in older women.

Older adulthood is accompanied by declines in muscular strength, coordination, function, and increased risk of falling. Resistance training increases muscular strength in this population but its effect on proprioception is unknown. To evaluate the effect of resistance training on proprioception, community dwelling older women completed a three-month exercise study. A resistance training (RT) group (N=19) underwent supervised weight training three times per week while a non-strength trained control (NSTC) group (N=19) performed range-of-motion activities that mimicked the movements of the RT group without the benefit of muscle loading. Subjects were evaluated at baseline, 6, and 12 weeks for strength and proprioception. Muscular strength was assessed by measuring the subject's one repetition maximum performance on four different exercises. Static proprioception was measured by the subject's ability to reproduce a target knee joint angle while dynamic proprioception was measured by the subject's ability to detect passive knee motion. The RT group made significant strength improvements compared to the NSTC group. Proprioception significantly improved in both groups by 6 weeks. Our findings suggest that improvements in proprioception can be obtained via regular activity that is independent of heavy muscle loading.

Relationship between quadriceps strength and rate of loading during gait in women.

One function of skeletal muscle is to serve as the body's shock absorbers and thus dampen rates of loading during activity. The aim of this cross-sectional study was to determine the significance of muscle strength on rates of loading during gait. Thirty-seven women (mean age: 34.5 +/- 8.2 years) were solicited by advertisement and placed into one of two groups-strength-trained or sedentary-on the basis of training history. They walked (10 trials) over a 10-m walkway at a controlled speed of 1.22-1.35 m/s while the rate of loading was sampled with a 1,000-Hz force platform. Quadriceps and hamstring strength was measured at 90 degrees/s with an isokinetic dynamometer. Statistical analyses (p < 0.05) included descriptive statistics and unpaired t tests for comparison between groups. The women in the sedentary group weighed more and had significantly less concentric and eccentric strength of the quadriceps and hamstrings relative to body weight than did those in the strength-trained group. In addition, they demonstrated significantly higher rates of loading (2.21 +/- 0.15 compared with 1.75 +/- 0.08%wt/ms) than those in the strength-trained group.

Differences in muscle endurance and recovery between fallers and nonfallers, and between young and older women.

BACKGROUND: Significant morbidity and mortality are associated with falls in older adults. We tested the hypothesis that older women with a history of falls demonstrate decreased muscle endurance and longer recovery times following fatiguing exercise. METHODS: We evaluated dynamic endurance and recoverability of the quadriceps femoris of 29 young women (YW) (M age = 21.7), 26 older women with a history of falls (FA) (M age = 73.3), and 27 older women with no history of falls (NF) (M age = 71.2) using an isokinetic dynamometer. Subjects performed repeated maximal concentric knee extensions until the force output of two consecutive repetitions fell below 50% of their maximal voluntary contraction (MVC). Recovery was defined as the time required for the return of force output > or = 80% MVC for 2 consecutive repetitions, within a set consisting of 3 maximal contractions. One minute rest was allowed between sets. We collected electromyographic (EMG) data from the quadriceps during all testing to evaluate spectral shifts. RESULTS: ANOVA with a post-hoc Bonferroni-Dunn test revealed time to fatigue was significantly faster in FA than YW (p < .02) and in FA than NF (p < .05), but not different between YW and NF. Time to recovery was significantly slower in FA than YW (p = .01), but not different between YW and NF, or between FA and NF, EMG median frequency power shift (from the beginning to the end of the test) was significantly less in FA (p < .001) than either YW (p < .002) or NF (p < .05). CONCLUSIONS: Older women with a history of falls demonstrate decreased muscular endurance compared to YW and NF, and increased time to recover from fatiguing exercise when compared to young women.

Eccentric and concentric strength of the shoulder and arm musculature in collegiate baseball pitchers.

Many pitching injuries occur during deceleration of the upper extremity when the muscles of the shoulder and arm are acting eccentrically. Published information regarding eccentric muscular strength in baseball pitchers is nonexistent. The purpose of this study was to assess bilateral isokinetic eccentric and concentric muscular strength of the shoulder's external and internal rotator muscles and the elbow's flexor and extensor muscles in a group of collegiate baseball pitchers (N = 25). Isokinetic strength was assessed at 1.6, 3.7, and 5.2 rad/sec. Our findings indicate that the internal rotator muscles were always stronger than the external rotator muscles and that the concentric and eccentric external-to-internal strength ratios ranged from 62% to 81%. The eccentric strength of the shoulder rotator muscles averaged 114% that of concentric strength. The concentric and eccentric elbow extension-to-flexion strength ratios ranged from 71% to 110%; eccentric strength averaged 33% higher than concentric strength. No differences were noted between dominant and nondominant limbs for any of the strength measures or ratios. Clinically, the findings of this study can serve as a reference during the evaluation, rehabilitation, and conditioning of throwing athletes.

Recovery of dynamic muscle function following isokinetic fatigue testing.

This study was designed to evaluate recovery of dynamic muscle function following muscle fatigue produced by isokinetic testing. Sixteen physically active males (age = 29.2) performed fatigue and recovery tests on an isokinetic dynamometer (KIN-COM 500H). The fatigue test involved concentric contractions of the quadriceps femoris performed until force output fell below 50% MVC for 3 consecutive contractions. This test was repeated 3 times, with 1 minute rest between sets. Recovery of force output was measured during the following 8 minutes. Following post hoc analysis, subjects were grouped into 1 of 3 groups based on their time to recovery of 80% MCV; Recovery immediately following fatigue exercise (Group 1), between 3 and 6 minutes (Group 2), or no recovery during the 8 minute period (Group 3). Analysis revealed a significant decline in peak force between bouts of a three-bout fatigue test for Groups 2 and 3 (p < 0.001), and no decline in Group 1. There was a significant relationship between decline in force output and time to recovery. Thus, subjects developing a greater amount of muscle fatigue took longer to recover following this isokinetic test. It was concluded that an isokinetic fatigue test to 50% MVC, repeated 3 times, is an appropriate fatigue generating protocol for most active males; that recovery time following isokinetic fatigue exercise varies among active males; and recovery may be directly related to decline in force output between bouts of a three-bout fatigue test.

Neuromuscular adaptations following prepubescent strength training.

Underlying mechanisms of prepubescent strength gains following resistance training are speculative. The purpose of this investigation was to determine the effects of 8 wk of resistance training on muscular strength, integrated EMG amplitude (IEMG), and arm anthropometrics of prepubescent youth. Sixteen subjects (8 males, 8 females) were randomly assigned to trained or control groups. All subjects (mean age = 10.3 yr) were of prepubertal status according to the criteria of Tanner. The trained group performed three sets (7-11 repetitions) of bicep curls with dumbbells three times per week for 8 wk. Pre- and posttraining measurements included isotonic and isokinetic strength of the elbow flexors, arm anthropometrics, and IEMG of the biceps brachii. Planned comparisons for a 2 x 2 (group by test) ANOVA model were used for data analysis. Significant isotonic (22.6%) and isokinetic (27.8%) strength gains were observed in the trained group without corresponding changes in arm circumference or skinfolds. The IEMG amplitude increased 16.8% (P < 0.05). The control group did not demonstrate any significant changes in the parameters measured. Early gains in muscular strength resulting from resistance training prepubescent children may be attributed to increased muscle activation.

Efficacy of a home-based training program for older adults using elastic tubing.

The purpose of this study was to investigate the efficacy of, and the adherence to, a 12-week home-based progressive resistance training program for older adults utilizing elastic tubing. Sixty-two adults (mean age, 71.2 years) qualified to participate in the study. Subjects were randomly assigned to either the exercise (E) (n = 31) or non-exercise (NE) group (n = 31). Pre- and post-testing included isokinetic (1.05 rad.s-1) concentric/eccentric knee extension/flexion strength testing and flexibility measures of the hip, knee, and ankle. The E group trained three times per week, performing one to three sets of 10-12 repetitions for each of 12 resistance exercises. The exercises involved muscles of both the lower and upper body. Within the E group, 25 of the 31 subjects (80.6%) completed the study. Of the E subjects completing the study adherence to the three training sessions per week was 90% (range 72%-100%). Training resistances used during workouts increased significantly with the average estimated increase being 82% (P < 0.001). The E group also demonstrated significant (P < 0.05) increases in isokinetic eccentric knee extension (12%) and flexion (10%) strength. No other significant changes were observed between E and NE groups. These results suggest that home-based resistance training programs utilizing elastic tubing can serve as a practical and effective means of eliciting strength gains in adults over the age of 65.

Energy balance in highly trained female endurance runners.

Anecdotal and scientific reports have suggested that some female endurance athletes may have an inexplicable imbalance between energy intake and energy expenditure. We compared energy intake (EI) from food diaries (FD) with assessment of free-living energy expenditure (EE) using doubly labeled water (DLW) and a food attitude survey for 7 d in nine female distance runners. Daily EE via DLW (2990 +/- 415 kcal) was greater (P < 0.01) than daily EI via FD (2037 +/- 298 kcal): a 32% imbalance. Body weight did not change during the 7 d (day 1, 55.3 +/- 6.2 kg; day 7, 55.1 +/- 5.6 kg). A positive relationship was observed between EE and body weight (r = 0.82) while a negative correlation existed between EE vs EI (r = -0.83) and between EI vs body weight (r = -0.74). A negative correlation was observed between body weight and food attitude/body image (r = -78), i.e., the heavier women self-reported lower EI and also reported lower body image scores. These female athletes had a significant imbalance between EI and EE by our measures. Since body image and EI were related to body weight, the estimates of EI may be low due to underreporting particularly by the heavier athletes.

Changes in muscle fiber size and composition in response to heavy-resistance exercise.

Progressive resistance exercise was used to induce hypertrophy in the right palmaris longus muscle (PLM) of 16 cats. The left PLM served as the non-exercised intra-animal control. After an average 150 +/- 26.6 wk of training, left and right PLMs were removed and weighed. Muscle fibers were typed using standard histochemical techniques. Mean fiber cross-sectional area, connective tissue content, and muscle fiber length were determined. The right exercised PLM demonstrated a 24.2 +/- 6.9% increase in muscle mass. Mean muscle fiber cross-sectional area increased 11.0 +/- 7.3% in the exercised muscles. No change in connective tissue content, fiber length, or fiber type composition was observed. The results show that increases in muscle fiber cross-sectional area do not account for all the observed increases in muscle mass, and that other mechanisms, such as muscle fiber hyperplasia, may play a role in contributing to muscle mass increases.