Maximum Volitional Contraction Research Articles

Method for Controlled Mitochondrial Perturbation during Phosphorus MRS in Children

Insulin resistance is increasingly prevalent in children and may be related to muscle mitochondrial dysfunction, necessitating development of mitochondrial assessment techniques. Recent studies used phosphorus magnetic resonance spectroscopy (P-MRS), a noninvasive technique appealing for clinical research. P-MRS requires exercise at a precise percentage of maximum volitional contraction (MVC). MVC measurement in children, particularly in those with a disease, is problematic because of variability in perception of effort and motivation. We therefore developed a method to predict MVC using maximal calf muscle cross-sectional area (MCSA) to assure controlled and reproducible muscle metabolic perturbations. Data were collected from 66 sedentary 12- to 20-yr-old participants. Plantarflexion MVC was assessed using an MRI-compatible exercise treadle device. MCSA of the calf muscles were measured from magnetic resonance images. Data from the first 26 participants were used to model the relation between MVC and MCSA (predicted MVC = 24.763 + 0.0047 MCSA). This model was then applied to the subsequent 40 participants. MVC versus model-predicted mean MVC was 43.9 ± 0.8 kg versus 44.2 ± 1.81 (P = 0.90). P-MRS results when predicted and MVC were similar showed expected changes during MVC-based exercise. In contrast, MVC was markedly lower than predicted in four participants and produced minimal metabolic perturbation. Upon repeat testing, these individuals could perform their predicted MVC with coaching, which produced expected metabolic perturbations. Compared with using MVC testing alone, using magnetic resonance imaging to predict muscle strength allows for a more accurate and standardized P-MRS protocol during exercise in children. This method overcomes a major obstacle in assessing mitochondrial function in youths. These studies have importance as we seek to determine the role of mitochondrial function in youths with insulin resistance and diabetes and response to interventions.

The Effect of Grip Span on Hand-Gripping Control Strength

The economic developments and industrial progressions, the automatic operations were getting more wide-spread. However, currently in various operation occasions, the workers are still required to face how to operate all kinds of hand tooling and equipments. In the industrial cases, there were many opportunities to use hand grip strength to operate machines. Hand grip strength has received increasing attention from industrial engineers and ergonomic researchers. The relation between hand grip strength and tools grip span was important issues in ergonomics. Occasionally, it was little research to conduct. This study aims at exploring the relationship of tools grip span and hand grip strength. Seventy two subjects rose from volunteers participators, including 29 males and 43 females. Dependent variables were maximum volitional contraction and hand gripping control (HGC-70%, target value 70% MVC). Three different diameters of grip span were significance differences in maximum volitional contraction and hand gripping control. The study finds that the best diameter of tools grip span was 47.6 mm. The finding will be served as a reference for task design, instrument design as well as for disease protected for industrial staffs.

The effects of glove thickness and work load on female hand performance and fatigue during a infrequent high-intensity gripping task

In various workplaces, gloves are commonly employed to protect the hands with the design rationale of ‘the thicker the gloves, the better the protection’. Therefore, the present paper investigated the effects of glove thickness on hand performance and fatigue during two infrequent high-intensity gripping tasks, such as 5-s and sustained tasks. The hand performance was evaluated by maximum volitional contraction (MVC) and its associated time needed to reach the MVC ( T MVC), and the total force generation (TFG) during the sustained task. The hand fatigue was assessed by MVC degeneration (ΔMVC), the shift in time needed to reach the MVC (Δ T MVC), and the maximal endurance time (MET) associated with the sustained task. Ten female subjects took part in the experiment voluntarily. The four-gloved conditions included bare hand, wearing one layer (Cotton-1), wearing two layers of cotton gloves (Cotton-2), and covering the handle with two layers of cotton glove and exerting with the bare hand (Covered-2). The results indicates that wearing gloves decreased the grip MVC, and the thicker the gloves, the less the grip MVC, but the wearing style did not change the MVC (Cotton-2 MVC was indifferent from Covered-2 MVC). As to muscular fatigue, on the other hand, wearing gloves did not affect ΔMVC, MET, T MVC, or Δ T MVC. Due to the greater bare-hand MVC and indifferent MET, bare-hand TFG was better than those conditions with gloves. Finally, the load specified here did not alter T MVC or Δ T MVC, but the greater the load, the more strength degeneration (ΔMVC) was induced.

Power and precision grip force control in three-to-five-year-old children: velocity control precedes amplitude control in development

The aim of this study was to examine the development of underlying motor control strategies in young children by characterizing the changes in performance of a visually guided force regulation task using two different grip formations; a whole-hand power grip (developmentally easier) and a thumb-index finger precision grip (developmentally more advanced). Typically developing preschool children (n=50, 3.0-5.5 years) used precision and power grips to perform a ramp and hold task with their dominant and non-dominant hands. Participants performed five trials with each hand and grip holding the force at 30% of their maximum volitional contraction for 3 s. The data were examined for both age-related and performance-related changes in motor performance. Across ages, children increased in strength, decreased in initial overshoot of the target force level, and decreased in rate of force release. Results of a cluster analysis suggest non-linear changes in the development of force control in preschool children, with a plateau in (or maturation of) velocity measures (rate of force increase and force decrease) earlier than in amplitude-related measures (initial force overshoot and force variability).

THE EFFECTS OF WRIST SPLINTS ON WHEN FEMALES REACH THE PEAK GRIP STRENGTH UNDER DIFFERENT WRIST AND FOREARM POSITIONS

ABSTRACT When peak grip strength is reached may be a useful and interesting index for evaluating strength generation and the relationship between resistance and response time, and as one of selected criteria to quantify the muscle fatigue and the static peak strengths. The present study investigates the influence of wearing splints under different forearm and wrist postures on grip MVC (maximum volitional contraction) as well as the time needed to reach the MVC (denoted by TMVC). Twenty female college students took part in this experiment voluntarily. The factorial design with four fixed factors (subject, forearm position, wrist deviation, and splint (with and without)) was employed. The forearm positions were set at 0 and 30 degrees internal (Internal-0 and 30) and 30 degrees external shoulder rotation (Ex-ternal-30). The wrist deviations are extension 30° (E30°), neutral (N0°), flexion 30° (F30°). The results show that the effect of forearm posture changes the grip MVC pronouncedly, but not the TMMVC. The forearm at External-30 generates the least MVC (234.5N), and the other two postures are indifferent from each other (250.3 N vs. 253.2 N). As to the effect of wrist posture, it influences both selected responses, the MVC and the TMVC. The wrist at neutral generates the optimum force (254.4 N), and the other two wrist postures are indifferent (239.6 N vs. 244.0 N). Moreover, wrist posture at E30° also has the longest TMVC, and the rate of force development is the lowest among the three specified wrist positions. Finally, the presence or absence of splints shifted neither the MVC nor the TMVC.

Practical and Effective Exercises on Human Musculoskeletal Systems in Weightless Environments

Weightless environments such as bedrest and spaceflight are associated with profound losses of muscle bulk and strength which hinder patient's or astronaut's health and reintegration into daily life. To prevent the losses, we developed a practical and effective training method with electrical stimulation, named “hybrid exercise”; electrical stimulations are added to antagonists at joints in order to produce resistance forces in one' s own body. The environment was simulated to evaluate the effects of the hybrid exercise on human body. An unilateral lower limb suspension (ULLS) was introduced as a simulation model of the weightless environment. Two kinds of experiments have been done : (1, ULLS experiment) only ULLS was executed to make disuse of lower limb. : (2, ULLS-Hybrid experiment) ULLS combined with the hybrid exercise to prevent losses of lower limb functions. We evaluated experiments by four items, maximum volitional contraction (MVC), cross-sectional area (CSA), bone mineral density (BMD), and electromyogram (EMG). The ULLS experiment showed dramatic losses of these parameters, whereas the ULLS-Hybrid experiment showed good effects of the hybrid exercise to prevent the losses.

EVALUATING THE EFFECTS OF SPLINT, PINCH TYPE, AND WRIST POSTURE ON PINCH STRENGTH

ABSTRACT Pinch strength applied in repetitive tasks was considered to be highly correlated with cumulative trauma disorders (CTDs). To reduce the magnitude requirement of pinch strength is important to avoid such injuries. But whether the peak pinch strength was affected by wearing wrist splints, sometimes used to protect the wrist from CTDs, is still unknown. This study, therefore, intended to evaluate the effect of wrist splints on the maximum volitional contraction (MVC) of pinch. A total of 24 right-handed volunteers (12 males, and 12 females) were recruited, and a nested-factorial design with subject nested within gender was employed. In addition to splint effect, effects of gender, wrist posture (extension 30°, flexion 30°, and neutral), and pinch type (Pulp2, Pulp3, Chuck, and Lateral) were evaluated, and all were considered as fixed variables. There were twenty-four combinations totally, and two replications were conducted. The ANOVA result showed the effects of gender, pinch type and their interaction were highly significant. But the effects of wrist posture and wrist splint were not. Male exerted much greater than female did under all pinch types, and female MVC was averagely about 56% (2.9kg/5.2kg) of male. For both genders, the MVC of Lateral was the largest, followed by Chuck, Pulp2, and Pulp3. Further according to the result of Duncan's multiple range test, female Lateral MVC and male Pulp2 MVC were not different significantly, as well as female Chuck MVC and male Pulp3 MVC. Wearing splints during repetitive tasks was recommended because it did not influence the pinch MVC or carpal tunnel pressure, and it can keep the wrist in neutral position as possible. In addition, the correlations between pinch MVC and anthropometry and among pinch types were discussed.

EVALUATING HEIGHT EFFECT ON ISOMETRIC LIFTING CAPABILITY OF YOUNG PEOPLE IN TAIWAN

ABSTRACT This study aimed to investigate the capability of is ometric lifting strength of young people in Taiwan at different exerting heights. Sixty volunteers including 30 males and 30 females were recruited. Three fixed independent variables including sex, subject (nested within sex), and lifting heights (ankle, knee, and knuckle) were investigated. The maximum volitional contraction (MVC) of lifting was considered as the dependent variable. The result of nested-factorial ANOVA indicates that sex and height factors affect lifting MVC significantly. Overall, female MVC is about 50% (331 N/666 N) of male regardless of specified heights. As to height effect, the ranking of these three levels is the same for both genders; lifting MVC at ankle level is the greatest (528 N), followed by at knuckle level (510 N, 97% of at ankle level), and the least is at knee level (459 N, 87% of at ankle level). On the other hand, lifting MVC does not correlate with grip MVC for both genders, but there is a correlation with body weight for male only (r=0.43, p<0.05). Above results can be useful for workplace design that requires heavy manual lifting, and for screening workers.