Maximal Torque Production Research Articles

Time Course of Mechanical and Neuromuscular Characteristics of Cyclists and Triathletes during a Fatiguing Exercise

This study examined the impact of sport specificity on the time course of fatigue during maximal voluntary eccentric, concentric and isometric torque production following a submaximal isokinetic fatiguing exercise. Seven cyclists and seven triathletes performed a fatiguing exercise consisting of nine sets of 31 isokinetic concentric knee extensions at 1.05 rad . s (-1). Fatigue was assessed pre-exercise, after three and six sets, and post-exercise. The maximal knee extension torque associated with electromyographic (EMG) activity was recorded during voluntary contractions and electrically induced contractions (single and paired twitches). The maximal voluntary eccentric torque production declined in cyclists (18 +/- 3.5 %, p < 0.05) and was not significantly affected in triathletes (5 +/- 2.5 %, p > 0.05). The decrease in cyclists was associated with an increase in the sum of the normalized EMG (nRMS) values of the three agonist muscles (p < 0.01). Although no significant difference was observed between groups, the two-way repeated-measure analysis of variance revealed a time effect on maximal concentric and isometric torque, twitch contractile and electrophysiological response (M (max)) properties. No modification in the activation and coactivation levels was observed. In conclusion, these results indicate that the time course of fatigue, especially during eccentric contractions, is mediated by sport-specific adaptations likely due to the mode of muscle contraction used in the activity.

Acute Effects of Static Stretching on Maximal Eccentric Torque Production in Women

The purpose of this study was to examine the acute effects of static stretching on peak torque (PT) and the joint angle at PT during maximal, voluntary, eccentric isokinetic muscle actions of the leg extensors at 60 and 180 degrees x s(-1) for the stretched and unstretched limbs in women. Thirteen women (mean age +/- SD = 20.8 +/- 0.8 yr; weight +/- SD = 63.3 +/- 9.5 kg; height +/- SD = 165.9 +/- 7.9 cm) volunteered to perform separate maximal, voluntary, eccentric isokinetic muscle actions of the leg extensors with the dominant and nondominant limbs on a Cybex 6000 dynamometer at 60 and 180 degrees x s(-1). PT (Nm) and the joint angle at PT (degrees) were recorded by the dynamometer software. Following the initial isokinetic assessments, the dominant leg extensors were stretched (mean stretching time +/- SD = 21.2 +/- 2.0 minutes) using 1 unassisted and 3 assisted static stretching exercises. After the stretching (4.3 +/- 1.4 minutes), the isokinetic assessments were repeated. The statistical analyses indicated no changes (p > 0.05) from pre- to poststretching for PT or the joint angle at PT. These results indicated that static stretching did not affect PT or the joint angle at PT of the leg extensors during maximal, voluntary, eccentric isokinetic muscle actions at 60 and 180 degrees x s(-1) in the stretched or unstretched limbs in women. In conjunction with previous studies, these findings suggested that static stretching may affect torque production during concentric, but not eccentric, muscle actions.

The effect of static and dynamic stretching exercises on the maximal isokinetic strength of the knee extensors and flexors

Warm-up and stretching exercises constitute an essential part of physical preparation before any athletic event. The aim of this study was to examine the acute effect of static and dynamic stretching exercises on maximal isokinetic torque of knee extensor and flexor muscles. Thirty-two (n = 32) physical education students aged 19-22 years were asked to perform three different protocols consisting of A) warm-up, B) warm-up and static stretching and C) warm-up and dynamic stretching exercises, on three non-consecutive days. Each treatment was followed by measurements of knee extensor and flexor muscles maximal concentric torque on an isokinetic dynamometer at 60 and 180 ◦ /s. ANOVA for repeated-measures revealed significant differences in maximal torque following the different protocols. Tukey's post hoc tests showed a reduced torque for knee extensor ( p< 0.01) and knee flexor muscles ( p< 0.01) at both velocities when static stretching exercises preceded the test. These findings indicate the negative influence of the static stretching exercises on maximal isokinetic torque production, while dynamic stretching approach does not seem to have any inhibitory effect.

A Preliminary Study of the Effects of Verbal Motivation on Maximal Isokinetic Torque Production in Children with Varying Personality Types

This study investigated the effects of verbal motivation on isokinetic peak torque knee extension in children with two distinct personality types (introvert versus extrovert). The subjects were tested in three groups without verbal motivation, with verbal motivation from the tester, and with verbal motivation from the tester and the other participants. A 2 − 3 mixed ANOVA was significant for interaction (p &lt; .001). Post-hoc testing for the introverted group revealed that scores without verbal motivation were significantly higher than with verbal motivation, and the extroverted group scores were higher with verbal motivation. T tests revealed that the extroverted group performed significantly better than the introverted group with verbal motivation (p &lt; .05). Results suggest that verbal motivation has a varying effect on isokinetic torque generating capacity in children with different personality types.

Changes in agonist EMG activation level during MVC cannot explain early strength improvement

A substantial gain in strength is often observed in the early phase of resistance training. The aim of this study was to address whether improved strength in the early phase of resistance training, can be attributed to increased activation, or to intra-muscular changes of the agonist muscle during maximal isometric torque production. Fourteen male subjects trained maximal isometric dorsiflexion during 5 days. Each subject performed 9 sessions with 25 maximal voluntary contractions in a device that registered the dorsiflexion torque. Surface electromyography (SEMG) of the tibialis anterior (TA) was recorded with a 130-channel grid electrode. SEMG of the extensor digitorum longus, gastrocnemius and soleus muscles were recorded with bipolar electrodes. The main finding was that all subjects gained in strength while the SEMG activation level of the primer agonist, TA, decreased with no apparent intra-muscular spatial changes following 5 days of resistance training. The other muscles that influence dorsiflexion torque did not modify their activation level with training. These findings reject an increase in agonist activation level as the main source for early strength gain, and illustrate the need for further research to reveal the specific sites of neural adaptation and other physiological mechanisms that might contribute to increased strength during the early phase of resistance training.

Time‐of‐Day Effect on the Torque and Neuromuscular Properties of Dominant and Non‐Dominant Quadriceps Femoris

The study was conducted first, to determine the possibility of a dichotomy between circadian rhythm of maximal torque production of the knee extensors of the dominant and non‐dominant legs, and second, to determine whether the possible dichotomy could be linked to a change in the downward drive of the central nervous system and/or to phenomena prevailing at the muscular level. The dominant leg was defined as the one with which subjects spontaneously kick a football. Tests were performed at 06:00, 10:00, 14:00, 18:00, and 22:00 h. To distinguish the neural and muscular mechanisms that influence muscle strength, the electromyographic and mechanical muscle responses associated with electrically evoked and/or voluntary contractions of the human quadriceps and semi‐tendinosus muscles for each leg were recorded and compared. The main finding was an absence of interaction between time‐of‐day and dominance effects on the torque associated with maximal voluntary contraction (MVC) of both quadriceps. A significant time‐of‐day effect on MVC torque of the knee extensors was observed for the dominant and non‐dominant legs when the data were collapsed, with highest values occurring at 18:00 h (p<0.01). From cosinor analysis, a circadian rhythm was documented (p<0.001) with the peak (acrophase) estimated at 18:18±00:12 h and amplitude (one‐half the peak‐to‐trough variation) of 3.3±1.1%. Independent of the leg tested, peripheral mechanisms demonstrated a significant time‐of‐day effect (p<0.05) on the peak‐torque of the single and doublet stimulations, with maximal levels attained at 18:00 h. The central activation of the quadriceps muscle of each leg remained unchanged during the day. The present results confirmed previous observations that muscle torque changes in a predictable manner during the 24 h period, and that the changes are linked to modifications prevailing at the muscular, rather than the neural, level. The similar rhythmicity observed in this study between the dominant and non‐dominant legs provides evidence that it is not essential to test both legs when simple motor tasks are investigated as a function of the time of day.

Quadriceps weakness in a family with nemaline myopathy: influence of knee angle.

Nemaline myopathy is a congenital neuromuscular disorder, which primarily affects the thin filaments. Clinically the most important feature is muscle weakness; however, this weakness is poorly understood. The present investigation aimed to determine the torque angle relationship of the knee extensor muscles during in vivo muscle contractions in a family with a novel phenotype of nemaline myopathy. The results of this study show that quadriceps weakness occurs predominantly at higher knee flexion angles, but relatively normal strength was found at angles closer to full knee extension. When the relative torque angle relationships were considered, torque loss at smaller than optimum knee flexion angle was greater in the patients compared with the controls. In addition, the optimum angle for maximal quadriceps torque production was shifted towards smaller knee flexion angles in the patients. This suggests that a weakness specifically at higher knee flexion angles probably occurs as a result of adaptations consequently to the disease. Furthermore, it is important to assess muscle function at different joint positions to allow adequate interpretation of muscle weakness.

IMPORTANCE OF SATELLITE CELLS IN RECOVERY FROM ECCENTRIC CONTRACTION-INDUCED INJURY

Eccentric contractions cause injury to skeletal muscle evidenced by prolonged decrements in force. Satellite cells are activated in response to eccentric contraction-induced injury, but their importance in the recovery of force after injury is unknown. PURPOSE To determine if satellite cells are required for the recovery of force after eccentric contraction-induced injury. METHODS Adult female ICR mice were implanted with a stimulating nerve cuff on the common peroneal nerve and assigned to one of four groups: 1) irradiation and eccentric contraction-induced injury (IRR/INJ, n = 11), 2) eccentric contraction-induced injury only (N-IRR/INJ, n = 10), 3) irradiation only (IRR/N-INJ, n = 11), and 4) no intervention (N-IRR/N-INJ, n = 8). Anterior crural muscles were irradiated with a dose of 2500 rad and injured 48 hr later with 150 in vivo maximal eccentric contractions during electrical stimulation. Maximal isometric torque was determined at 0, 7, 14, 21, 28, and 35 days after the induction of injury. Group × time comparisons were made using a two-way ANOVA with repeated measures over time. RESULTS Maximal isometric torque production by N-IRR/INJ mice was not different from control animals by day 28 after injury induction (2.82 ± 0.37 vs. 2.91 ± 0.36 N mm). However, maximal isometric torque production of IRR/INJ animals did not recover and was less than N-IRR/INJ at 14 (19%), 21 (16%), 28 (21%), and 35 (25%) days after injury. CONCLUSION Satellite cells are required for normal force recovery following eccentric contraction-induced injury.

THE EFFECT OF FOREARM FLEXION ANGLE ON THE MMG AND EMG AMPLITUDE

PURPOSE The purpose of this study was to examine the mechanomyographic (MMG) amplitude-isometric torque relationship of the biceps brachii at three different joint angles. METHODS Twelve adult females (21±2 yrs) performed isometric muscle actions of the dominant forearm flexors on a Cybex II Dynamometer at 25, 50, 75, and 100% maximal voluntary contraction at joint angles of 30, 60, and 90° above the horizontal plane. MMG and EMG signals were recorded from the mid-portion of the biceps brachii using a piezoelectric contact sensor and a bipolar surface electrode arrangement, respectively. RESULTS Initial examination of the maximal isometric torque data suggested the presence of two different groups based on angle where maximal torque was produced. A one-way mixed factorial ANOVA indicated significant (p < 0.05) differences between the subjects such that six subjects (group A) recorded the highest maximal torque at 60° while the remaining six (group B) at 90°. Further, in comparison to group B, the maximal torque at 30 and 60° was significantly (p < 0.05) greater for group A. Examination of the EMG and MMG amplitude patterns across level of force indicated the EMG amplitude patterns for both groups increased up to 100%MVC at each joint angle. The MMG amplitude pattern increased up to 100% MVC at each jont angle for group A. For group B, however, the MMG amplitude decreased or plateaued between 75 and 100% MVC at 30 and 60° and increased up to 100% MVC at 90°. CONCLUSION These findings suggest that the amplitude patterns of the MMG signal from the biceps brachii may be joint angle dependent and associated with the variations in the magnitude of isometric torque production at multiple joints angles. Future investigations should consider evaluating the MMG amplitude-isometric torque relationship for unique groups based on angle of maximal torque production.

Impaired performance of skeletal muscle in alpha-glucosidase knockout mice.

Glycogen storage disease type II (GSD II) is an inherited progressive muscle disease in which lack of functional acid alpha-glucosidase (AGLU) results in lysosomal accumulation of glycogen. We report on the impact of a null mutation of the acid alpha-glucosidase gene (AGLU(-/-)) in mice on the force production capabilities, contractile mass, oxidative capacity, energy status, morphology, and desmin content of skeletal muscle. Muscle function was assessed in halothane-anesthetized animals, using a recently designed murine isometric dynamometer. Maximal torque production during single tetanic contraction was 50% lower in the knockout mice than in wild type. Loss of developed torque was found to be disproportionate to the 20% loss in muscle mass. During a series of supramaximal contraction, fatigue, expressed as percentile decline of developed torque, did not differ between AGLU(-/-) mice and age-matched controls. Muscle oxidative capacity, energy status, and protein content (normalized to either dry or wet weight) were not changed in knockout mice compared to control. Alterations in muscle cell morphology were clearly visible. Desmin content was increased, whereas alpha-actinin was not. As the decline in muscle mass is insufficient to explain the degree in decline of mechanical performance, we hypothesize that the large clusters of noncontractile material present in the cytoplasm hamper longitudinal force transmission, and hence muscle contractile function. The increase in muscular desmin content is most likely reflecting adaptations to altered intracellular force transmission.

Inhibition of Maximal Voluntary Isokinetic Torque Production Following Stretching Is Velocity-Specific

Recent research has shown that a regimen of stretching provides an acute inhibition of maximal force production by the stretched muscle group. To further characterize this phenomenon, the effect of an acute stretching regimen on maximal isokinetic knee-extension torque at 5 specific movement velocities (1.05,1.57, 2.62, 3.67, and 4.71 rad·s−1) was examined in 10 men and 5 women (22–28 years). Each person's 5 baseline maximal isokinetic knee-extension torques (dominant leg) were measured on a Cybex NORM dynamometer. Following the baseline torque measurements, the participants stretched the dominant quadriceps for 15 minutes using 1 active and 3 passive stretching exercises. Once the stretching exercises were completed, the maximal torque measurements were repeated. Poststretch maximal torque at 1.05 rad·s−1 was significantly reduced (p < 0.05) from 218 ± 47 Nm (mean ± SD) to 199 ± 49 Nm (7.2% decrease). At 1.57 rad·s−1, a similar decrease (p < 0.05) was also seen (204 ± 48 Nm vs. 195 ± 47 Nm; 4.5% decrease), but at the other velocities (2.62, 3.67, and 4.71 rad·s−1), poststretch maximal torque was unaltered (p > 0.05). It appears, therefore, that the deleterious impact of stretching activities on maximal torque production might be limited to movements performed at relatively slow velocities.

Inhibition of Maximal Voluntary Isokinetic Torque Production Following Stretching Is Velocity-Specific

Recent research has shown that a regimen of stretching provides an acute inhibition of maximal force production by the stretched muscle group. To further characterize this phenomenon, the effect of an acute stretching regimen on maximal isokinetic knee-extension torque at 5 specific movement velocities (1.05, 1.57, 2.62, 3.67, and 4.71 rad x s(-1)) was examined in 10 men and 5 women (22-28 years). Each person's 5 baseline maximal isokinetic knee-extension torques (dominant leg) were measured on a Cybex NORM dynamometer. Following the baseline torque measurements, the participants stretched the dominant quadriceps for 15 minutes using 1 active and 3 passive stretching exercises. Once the stretching exercises were completed, the maximal torque measurements were repeated. Poststretch maximal torque at 1.05 rad x s(-1) was significantly reduced (p < 0.05) from 218 +/- 47 Nm (mean +/- SD) to 199 +/- 49 Nm (7.2% decrease). At 1.57 rad x s(-1), a similar decrease (p < 0.05) was also seen (204 +/- 48 Nm vs. 195 +/- 47 Nm; 4.5% decrease), but at the other velocities (2.62, 3.67, and 4.71 rad x s(-1)), poststretch maximal torque was unaltered (p > 0.05). It appears, therefore, that the deleterious impact of stretching activities on maximal torque production might be limited to movements performed at relatively slow velocities.

Increasing Involuntary Torque Production by Using TENS

The opinions and assertions contained herein are the private views of the authors, and are not to be construed as official or as reflecting the views of the Departments of the Army, Navy, or Defense. The purpose of this study was to evaluate the effects of low-amplitude electrical stimulation (ES) on maximal tolerable ES and involuntary torque production of the quadriceps femoris muscle. Seventeen healthy volunteers (11 male, 6 female) aged 19-35 years (mean, 25.1 years) completed the study. Both quadriceps femoris muscle groups received maximal tolerated ES in all subjects. One limb was treated with 10 minutes of low-amplitude ES prior to application of the maximal tolerated ES, while the opposite limb did not receive the low-amplitude ES. Analysis of the data revealed significantly (p < 0.01) greater torque generation and current tolerated when the maximal tolerated ES was delivered following the low-amplitude ES. The clinical implication is that if ES is to be used to increase muscular strength, a low-amplitude current delivered prior to maximal tolerable current delivery allows greater involuntary torque production. J Orthop Sports Phys Ther 1990;12(3):101-104.

Trunk Strength during Asymmetric Trunk Motion

It is important to understand how trunk strength varies as a function of workplace factors so that the work environment can be designed to minimize the risk of low back injury. In this study maximal trunk torque production around the lumbosacral junction was measured in 44 subjects as trunk concentric and eccentric isokinetic velocity and trunk asymmetric line of action were varied. Trunk torque decreased by approximately 8.5% of maximum for every 15 deg of asymmetric trunk angle. Increases in concentric velocity decreased trunk strength, whereas increases in eccentric trunk velocity increased strength. Significant interactions were also found, and it was determined that the common finding that eccentric strength exceeds concentric strength is true only for forward trunk angles at all asymmetric angles. These results should have significant implications for the design of manual materials handling tasks.