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This study investigated the effect of an 8-week neuromuscular electrical stimulation (NMES) training programme (3 days/week) on muscle quantity and quality and single-joint performance in the knee extensors. Thirty-nine untrained young male participants were randomly assigned to NMES training (n = 21) and control (n = 18) groups. The 8-week NMES training induced significant increase in the isometric maximal voluntary contraction (MVC) torque of the knee extensors (≈9.3%), muscle volume of the individual and entire quadriceps muscles determined by magnetic resonance imaging (≈3.3%–6.4%), and a significant decrease in the ultrasound echo intensity of the vastus lateralis (≈−4.0%); however, hypertrophy of the vastus intermedius (i.e., the deep muscle) was limited (≈3.3%). In the NMES training group, the repeated measures correlations of the isometric MVC torque with the muscle volume of the entire quadriceps muscle and each quadriceps muscle were significant (rrm (20) = 0.551–0.776), whereas that of the isometric MVC torque with the ultrasound echo intensity of the vastus lateralis was not significant. These findings suggest that NMES training produces muscle strength gains, muscle hypertrophy, and partial muscle quality improvement and that the NMES training-induced muscle strength gains is caused by muscle hypertrophy in the knee extensors. [ABSTRACT FROM AUTHOR]

Shoulder strength is reduced in older adults but has only been assessed in planar motions that do not reflect the diverse requirements of daily tasks. We quantified the impact of age on strength spanning the three degrees of freedom relevant to shoulder function, referred to as the feasible torque space. We hypothesized that the feasible torque space would differ with age and expected this age-effect to reflect direction-specific deficits. We measured strength in 32 directions to characterize the feasible torque space of the shoulder in participants without shoulder pain or tendinous pathology (n = 39, 19–86 years). We modeled the feasible torque space for each participant as an ellipsoid, computed the ellipsoid size and direction-specific metrics (ellipsoid position, orientation, and shape), and then tested the effect of age on each metric. Age was negatively associated with ellipsoid size (a measure of overall strength magnitude; −0.0033 ± 0.0007 (Nm/kg)/year, p < 0.0001). Contrary to our expectation, the effect of age on the direction-specific metrics did not reach statistical significance. The effect of age did not differ significantly between male and female participants. Three-dimensional strength measurements allowed us to constrain the direction of participants' maximum torque production and characterize the entire feasible torque space. Our findings support a generalized shoulder strengthening program to address age-related shoulder weakness in those without pain or pathology. Clinical exam findings of imbalanced weakness may suggest underlying pathology beyond an effect of age. Longitudinal studies are needed to determine the positive or negative impact of our results. [ABSTRACT FROM AUTHOR]

Objective: The torque-producing capacity can be assessed as maximal isometric torque per muscle size. Nevertheless, the factors contributing to this capacity remain poorly understood. In general, the magnitude of joint torque production is determined not only by muscle size but also by joint moment arm (MA). Based on this background, we hypothesized that longer MA would be related to higher torque-producing capacity despite a given muscle size. To test this hypothesis, we examined the relationship between MA and toque-producing capacity in the knee extensors. The quadriceps femoris muscle volume (MV) and knee extensor MA in 30 healthy young men were measured using magnetic resonance imaging. The knee extensor isometric torque was measured using a dynamometer. The knee extensor torque-producing capacity was calculated as the knee extensor isometric torque per quadriceps femoris MV. Results: The quadriceps femoris MV and knee extensor MA correlated significantly with the knee extensor isometric torque (r = 0.785 and 0.790, respectively, both Ps < 0.001). Furthermore, the knee extensor MA correlated significantly with the knee extensor torque-producing capacity (r = 0.635, P < 0.001). These findings suggest that longer MA is an important factor for achieving higher torque-producing capacity in the human knee extensors. [ABSTRACT FROM AUTHOR]

This study determined whether disrupted glucose and insulin responses to an oral glucose-tolerance test (OGTT) induced by eccentric exercise were attenuated after a repeated bout. Female participants (n = 10, age 24.7 ± 3.0 yr, body mass 64.9 ± 7.4 kg, height 1.67 ± 0.02 m, body fat 29% ± 2%) performed 2 bouts of downhill running (DTR 1 and DTR 2) separated by 14 d. OGTTs were administered at baseline and 48 hr after DTR 1 and DTR 2. Maximum voluntary isometric quadriceps torque (MVC), subjective soreness (100-mm visual analog scale), and serum creatine kinase (CK) were assessed pre-, post-, and 48 hr post-DTR 1 and DTR 2. Insulin and glucose area under the curve (38% ± 8% and 21% ± 5% increase, respectively) and peak insulin (44.1 ± 5.1 vs. 31.6 ± 4.0 μU/ml) and glucose (6.5 ± 0.4 vs. 5.5 ± 0.4 mmol/L) were elevated after DTR 1, with no increase above baseline 48 hr after DTR 2. MVC remained reduced by 9% ± 3% 48 hr after DTR 1, recovering back to baseline 48 hr after DTR 2. Soreness was elevated to a greater degree 48 hr after DTR 1 (48 ± 6 vs. 13 ± 3 mm), with a tendency for greater CK responses 48 hr after DTR 1 (813 ± 365 vs. 163 ± 43 U/L, p = .08). A novel bout of eccentric exercise confers protective effects, with subsequent bouts failing to elicit disruptions in glucose and insulin homeostasis. [ABSTRACT FROM AUTHOR]

Tibiotalar arthrodesis is commonly used to treat end‐stage ankle osteoarthritis. Post‐operative impairments are often attributed to limited ankle motion. However, whether muscular deficits also exist, thereby potentially contributing to impairments, is unknown. This study aimed to identify post‐operative deficits in ankle musculature by examining range of motion, strength (maximum isometric ankle joint torque), and leg composition (cross‐sectional area of individual tissue types: bone, subcutaneous adipose, intramuscular adipose, muscle). Ten individuals with unilateral tibiotalar arthrodesis participated. Paired t‐tests (p < 0.05) identified differences between the fused and contralateral, control limb. The results indicate that individuals with tibiotalar arthrodesis have profound losses of range of motion and strength. Across participants, range of motion in the fused limb was 53.5 ± 11.7%, 66.8 ± 6.3%, 38.2 ± 18.7%, 37.8 ± 13.6% less than the control for dorsiflexion, plantarflexion, inversion, and eversion, respectively. The largest strength deficit was in dorsiflexion, with the fused limb producing 47.2 ± 9.4% less torque than the control. The quantity and quality of muscle tissue was also negatively affected in individuals following tibiotalar arthrodesis. The total cross‐sectional area of the fused limb was 11.4 ± 5.4% smaller than the control limb. This change was primarily due to the 16.1 ± 6.7% decrease in muscle cross‐sectional area. However, intramuscular adipose was significantly increased. Although the posterior compartment demonstrated a significant decrease in cross‐sectional area, when accounting for differences in total cross‐sectional area, the relative sizes of the four muscle compartments were consistent between limbs. This cross‐sectional study motivates longitudinal research examining muscular deficits and whether these deficits are reversible with exercise and rehabilitation. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res [ABSTRACT FROM AUTHOR]

Highlights • Children at rDCD use feedback to improve their ability to fine-tune. • Children at rDCD are more dependent of the visual feedback than TD children. • Children at rDCD are more variable than TD children on fine-tune after practice. Abstract Background The production of finger force control is essential for a large number of daily activities. There is evidence that deficits in the mechanisms of accuracy and control of finger force tasks are associated with children's motor difficulties. Objective To compare the effect of practice of an isometric finger force/torque task between children with significant movement difficulty and those with no difficulty movement. Methods Twenty-four children aged between 9 and 10 years (12 at risk of developmental coordination disorder and 12 with no movement difficulty – typically developing children) were asked to produce finger force/torque control in a continuous and constant 25% of maximum voluntary torque with visual feedback during 15 s. Practice was given during five consecutive days with 15 trials per day. After the practice with visual feedback, children were asked to perform five trials without visual feedback. In these trials, feedback was removed 5 s after the start of the trial. Results Typically developing children were consistently more accurate in maintaining finger force/torque control than those children at risk of developmental coordination disorder. Children from both groups improved the performance in the task according to practice sessions. Also, children at risk of developmental coordination disorder poorly performed the task without visual feedback as they did when visual feedback was available. Conclusion The present study give support to the idea that movement difficulty is associated with finger force/torque control and children at risk of developmental coordination disorder can improve finger force/torque control with practice when visual feedback is available. [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine whether the mechanical contribution of ankle muscles in the upright stance differed among young adults (YA) (n = 10, age: ~ 24.3), elderly non-fallers (ENF) (n = 12, age: ~ 77.3) and elderly fallers (EF) (n = 20, age: ~ 80.7). Torque and electromyographic (EMG) activity were recorded on the triceps surae and tibialis anterior during maximum and submaximum contractions in the seated position. EMG activity was also recorded in subjects standing still. Plantar flexor (PF) and dorsal flexor (DF) torques generated in the upright posture were estimated from the torque–EMG relationship obtained during submaximum contractions in the seated position. Center of pressure (CoP) displacement was measured to quantify postural stability. Results showed that, in upright standing, EF generated greater ankle muscle relative torque (i.e. PF + DF torque in the upright stance/PF + DF during maximum isometric torque) than non-fallers (i.e. ENF, YA). The greater involvement of ankle muscles in EF was associated with higher CoP displacement. PF + DF torque in the upright stance was no different among the groups, but PF + DF torque during maximum effort was impaired in older groups compared with YA and was lower in EF than ENF. These results suggest that the postural stability impairment observed with aging is highly related to ankle muscle weakness. [ABSTRACT FROM AUTHOR]

The stress inducible 70 kDa heat shock protein (Hsp70) is instrumental to efficient morphological and functional recovery following skeletal muscle injury because of its roles in protein quality control and molecular signalling. Therefore, in attempt to improve recovery, Hsp70 expression was increased with 17-(allylamino)-17-demethoxygeldanamycin (17-AAG) prior to and following an intramuscular injection of barium chloride (BaCl2) into the tibialis anterior (TA) of healthy young mice. To assess recovery, regenerating fibre cross-sectional area (CSA) of the TA and in vivo peak isometric torque produced by the anterior crural muscles (TA, extensor digitorum longus and extensor hallucis muscles) were analyzed for up to 3 weeks after the injury. Because treatment of 17-AAG and Hsp70 are known to influence inflammatory and myogenic signalling, tumor necrosis factor-α (TNF-α) and myogenin content were also assessed. This study reports that 17-AAG was effective at up-regulating Hsp70 expression, increasing content fivefold in the uninjured muscle. However, this significant increase in Hsp70 content did not enhance morphological or functional recovery following the injury, as the return of regenerating fibre CSA and in vivo peak isometric torque did not differ compared to that of the injured muscle from the vehicle treated mice. Treatment with 17-AAG also altered TNF-a and myogenin content, increasing both to a greater extent after the injury. Together, these findings demonstrate that although 17-AAG may alter molecular makers of regeneration, it does not improve recovery following BaCl2-induced skeletal muscle injury in healthy young mice. [ABSTRACT FROM AUTHOR]

Purpose: The present study examined neuromuscular adaptations following 12-week maximal voluntary co-contraction training. Methods: Sixteen young men were allocated to training (TG, n = 9) or control (CG, n = 7) group. TG conducted a training program (3 days/week), which consisted of 4-s maximal voluntary contractions of elbow flexors and extensors by simultaneously contracting both muscle groups at 90° of the elbow joint, followed by 4-s muscle relaxation (10 repetitions/set, 5 sets/day) for 12 weeks. In addition to the muscle thicknesses of elbow flexors and extensors, the torque and electromyograms (EMGs) of the two muscle groups during isometric maximal voluntary contraction (MVC) were determined before (Pre), after 4 weeks, and 12 weeks of intervention. Results: After intervention, CG showed no significant changes in all measured variables. In TG, MVC torque significantly increased in both elbow flexors (+13 % at 4 weeks and +15 % at 12 weeks) and extensors (+27 % at 4 weeks and +46 % at 12 weeks) from Pre. Muscle thickness also significantly increased in both elbow flexors (+4 %) and extensors (+4 %) at 12 weeks. Agonist EMG activities during MVC significantly increased in both elbow flexors (+31 % at 4 weeks and +44 % at 12 weeks) and extensors (+27 % at 4 weeks and +40 % at 12 weeks), without changes in antagonist involuntary coactivation level in both muscle groups. Conclusion: These results indicate that maximal voluntary co-contraction is applicable as a training modality for increasing the size and strength of antagonistic muscle pairs without increasing involuntary coactivation level. [ABSTRACT FROM AUTHOR]

Both isotonic and isokinetic eccentric muscle contractions are commonly used in muscle research laboratories to induce muscle damage, yet, the muscle damage outcomes between these 2 modes of eccentric contraction have not been compared. The purpose of this study was to compare modes of contraction for differences in muscle damage. 16 men were placed in the isotonic (IT: 110 % of maximal isometric torque) or the isokinetic (IK: 120 °/s) group, with each group performing 200 eccentric muscle actions of the knee extensors. Isometric peak torque, perceived soreness and CK activity were measured immediately pre and post exercise, and 48-h post exercise. Mean total work (~1 700 J) and peak torque per set (~265 Nm) decreased over the 200 repetitions (p < 0.01), and was not different between groups. Damage markers changed 48-h post exercise (p < 0.05): peak isometric torque ( - 13 %), creatine kinase activity ( + 200 %) and self-perceived muscular soreness ( + 4 unit change). Significant group × time interactions (p < 0.01) indicated that peak isometric torque was 22 % lower, and creatine kinase and self-perceived muscular soreness were 330 % and 3 unit difference higher in the IT as compared to the IK groups, 48-h post exercise. When equating for total work, skeletal muscle damage markers are higher during IT vs. IK modes. This reflects differences inherent in contraction type and suggests that this should be taken into account during physical rehabilitation. [ABSTRACT FROM AUTHOR]

The purposes of this study were to determine 1) whether sex differences in quadriceps torque and isotonic power persist when controlling for muscle volume (i. e., torque/muscle volume and power/muscle volume) in participants with knee osteoarthritis (OA) and 2) the factors responsible for potential sex differences. Isometric torque, isotonic power (the product of torque and velocity, measured at 10, 20, 30, 40 and 50 % maximal voluntary contraction; MVC) and maximal unloaded velocity were assessed in men (n = 16, mean age = 62.1 ± 7.2) and women (n = 17, mean age = 60.4 ± 4.3) with knee OA. Torque and power were normalized to muscle volume. The interpolated twitch technique was used to measure voluntary activation (VA) and evoked twitch and torque-frequency characteristics were measured to obtain information about muscle fibre distribution. Torque and power at all loads were significantly lower in women (p < 0.05). Sex differences in power were reduced by 50 % when controlling for muscle volume but were still significant at 10-40 % MVC (p < 0.05). No differences in VA, torque-frequency properties or time-to-peak tension of the evoked twitch were observed (p > 0.05). These results suggest that only minor sex differences in torque and power persist when controlling for muscle volume. As VA and contractile property differences were not observed, other factors seem to be responsible. [ABSTRACT FROM AUTHOR]

A hand cranking mechanical frictional setup was developed using anthropometric dimensions of Madhya Pradesh farm women. The setup had a provision for attaching on-line torque transducer. Variable crank length was provided that could be adjusted as per the farm women (workers). The setup had also a provision for rising up and down to match workers’ conditions. Isometric torque was measured at each quadrant positions of handle (0°, 90°, 180° and 270°) at different crank lengths (17.5, 21, 24, 27 and 30 cm). Higher torque was developed by farm women in standing posture as compared to sitting. The crank length up to 27 cm gave better torque at nearly all positions. The lowest torque may be considered for designing the equipment amongst all positions of handle so that human being could easily operate the equipment. [ABSTRACT FROM AUTHOR]

The present study examined whether the strength capability of knee extensor muscles is associated with global cognitive function, assessed by Mini-Mental State Examination (MMSE), in non-disabled elderly men. Isometric torques during maximal voluntary knee extension, plantar flexion, and elbow flexion and MMSE scores were determined in 39 non-disabled men aged 61-79 years and used for the cross-sectional analysis examining the associations among the measured variables. Moreover, 27 of the subjects participated in a training program consisted of body mass-based exercises (sitting down onto and standing up from a chair , hip joint extension and flexion, calf raises, side leg raises, and trunk flexion and extension) 6 days a week for 3 months. Isometric torques and MMSE scores were determined after the intervention. Among the data before intervention, only knee extension torque (KET) and KET relative to body mass (KET/BM) significantly correlated to the MMSE scores: r = 0.579 ( P < 0.0001) for KET and r = 0.520 ( P < 0.001) for KET/BM. After the intervention, KET and KET/BM increased significantly, but MMSE score did not. However, the absolute change in MMSE scores was significantly associated with that in KET ( r = 0.381, P < 0.05) and KET/BM ( r = 0.422, P < 0.05). These findings indicate that the strength capability of knee extensors is associated with global cognitive function in non-disabled elderly men, and provide a new perspective to a general concept that exercises strengthening knee extensor muscles should be included in resistance training programs for elderly individuals. [ABSTRACT FROM AUTHOR]

Abstract: Objective: Using “painless” magnetic stimulation (FMS) to support the cycling of paretic subjects with preserved sensation is possible and potentially superior to electrical stimulation (FES). We investigated the dependence of the torque and the pain evoked by FMS and FES on stimulation conditions in order to optimize magnetic stimulation. Methods: Torque and pain induced by quadriceps stimulation in 13 subjects with paresis and preserved sensation (due to multiple sclerosis) were compared under the conditions: (1) small vs large stimulated surfaces of the thigh, (2) varying contraction velocities of the muscle (isometric vs 15 and 30rpm isokinetic speed), (3) FMS vs FES modalities, and (4) varying magnetic coil locations. Results: Torque and pain significantly depended on the amount of surface and location of stimulation during FMS, on the stimulation modality, and on the muscle contraction velocity during FES and FMS. FMS with a saddle-shaped coil produced more torque (p <0.05) than any other stimulation modality, even at 30rpm velocity. Conclusions: To support leg cycling of subjects with preserved sensation, the application of FMS stimulation with a large-surface saddle-shaped coil and the focusing of stimulation on the lateral-frontal surface of the thigh produces greater torque and less pain than FES. Significance: Optimized magnetic stimulation is a superior alternative to electrical stimulation in the rehabilitation of subjects with preserved sensation. [ABSTRACT FROM AUTHOR]

The article presents a study on the relationship between musculotendinous unit stiffness and isometric rate of torque development (RTD) in sprint cycling. The study evaluated the maximal isometric torque (MIT) and isometric RTD of the quadriceps of 21 trained cyclists. It also measured the unilateral musculoarticular (MA) stiffness of the quadriceps by means of an oscillation test. The results of the study reveal that higher stiffness is associated to superior rate of crank torque development (RCTD)peak in single sprint cyclist. It also says that a significant proportion of the RCTDpeak variance was attributed to MA stiffness.

This study intended to take a biomechanical approach to understand the success of Kenyan distance runners. Anthropometric, gait and lower extremity strength characteristics of six elite Kenyan distance runners were analyzed. Stride frequency, relative stride length and ground contact time were measured at five running speeds (3.5 - 5.4 m/s) using a motion capture system. Isometric knee extension and flexion torques were measured at six angles and hamstrings and quadriceps (H:Q) ratios at three angular velocities were determined using an isokinetic dynamometer. These runners were characterized by a low body mass index (20.1 ± 1.8 kg·m-2), low percentage body fat (5.1 ± 1.6%) and small calf circumference (34.5 ± 2.3 cm). At all running speeds, the ground contact time was shorter (p < 0.05) during right (170 - 212 ms) compared to left (177 - 220 ms) foot contacts. No bilateral difference was observed in other gait or strength variables. Their maximal isometric strength was lower than other runners (knee extension: 1.4 - 2.6 Nm·kg-1, knee flexion: 1.0 - 1.4 Nm·kg-1) but their H:Q ratios were higher than athletes in other sports (1.03 ± 0.51 at 60°/s, 1.44 ± 0.46 at 120°/s, 1.59 ± 0.66 at 180°/s). The slim limbs of Kenyan distance runners may positively contribute to performance by having a low moment of inertia and thus requiring less muscular effort in leg swing. The short ground contact time observed may be related to good running economy since there is less time for the braking force to decelerate forward motion of the body. These runners displayed minor gait asymmetry, though the difference may be too small to be practically significant. Further investigations are needed to confirm whether the bilateral symmetry in strength and high H:Q ratios are related to genetics, training or the lack of injuries in these runners. [ABSTRACT FROM AUTHOR]

Abstract: Background: Cycling is a safe and functionally effective exercise for patients with early post-stroke and poor balance. Such exercise is considered even more effective when functional electrical stimulation is added. Our principal aim was to determine the biomechanically quantifiable parameters of cycling that can be improved in patients with subacute hemiparesis by incorporating functional electrical stimulation. These parameters were defined as objective goals that can be achieved in clinical applications. A secondary aim was to determine whether they could be used to identify subjects who would benefit from such therapy. Methods: Using a tricycle testbed, we tested 39 subacute (mean 10.9 weeks post-stroke (SD 5.9)), hemiplegic subjects. During isometric measurements we recorded volitional and electrically evoked crank torques, the latter at maximal tolerable intensity. During ergometric measurements, volitional pedaling was alternated with combined pedaling (volitional supported by stimulation), performed at 30-s intervals. Power, smoothness, and symmetry of cycling were evaluated. Findings: Twenty-six percent of the subjects significantly improved the smoothness of their cycling with functional electrical stimulation. Only 8% and 10% significantly increased their power and symmetry, respectively. The improvement in smoothness significantly correlated with the capability of the individual to generate electrical torque (Spearman’s rank correlation coefficient=0.66 at P =0.001). Interpretation: The smoothness of cycling was the most sensitive parameter improved by functional electrical stimulation. This improvement depended on the amount of torque evoked, and the torque achieved, in turn, correlated with the tolerated intensity of stimulation. [Copyright &y& Elsevier]

This study investigated whether 10 drop jumps (DJs) would confer protective effect against muscle damage and soreness in a subsequent bout of 50 DJs. Sixteen men were randomly placed into either a group performing 1 set of 10 DJs followed by 5 sets of 10 DJs (10-50, n = 8) or another group performing 2 bouts of 5 sets of 10 DJs (50-50, n = 8) separated by 2 weeks. The DJs were performed from a box height of 0.6 m, with a 10-second interval between jumps and a 1-minute rest between sets. Jump height, peak vertical ground reaction force, ground contact time, and heart rate during DJs were measured, and blood lactate concentration was assessed before and immediately after DJs. Changes in maximal isometric (ISO) and isokinetic concentric torque (CON), vertical jump, muscle soreness, and plasma creatine kinase activity before, immediately after, and at 1, 24, 48, and 72 hours following exercise were compared between groups for the first and second bouts and between the bouts by a 2-way repeated-measures analysis of variance. Changes in ISO, CON, vertical jump, and muscle soreness were significantly (p < 0.05) smaller for 10 DJs compared with 50 DJs; however, no signifi- cant differences in the measures between groups were evident following the second bout. The changes in the measures following 50 DJs in the 10-50 group were significantly (p < 0.05) smaller than those following the first bout of the 50-50 group. These results suggest that 10 DJs and 50 DJs conferred the same magnitude of protective effect against muscle damage by 50 DJs. [ABSTRACT FROM AUTHOR]

Joint mobilization and manipulation stimulate mechanoreceptors, which may influence the joint and surrounding muscles. The purpose of this pilot study was to determine the effect of grade IV inferior hip joint mobilization on hip abductor torque. Thirty healthy subjects were randomly assigned to a control group (grade I inferior hip joint mobilization) or an experimental group (grade IV inferior hip joint mobilization). Subjects performed a pre- and post-intervention test of five isometric repetitions on the Cybex Normö dynamometer; the average torque was determined for both pre- and post-intevention measurements. These data were analyzed using the independent samples t-test with the significance level set at P<0.05. The results showed a statistically significant difference between the two groups for an increase in hip abductor torque in the experimental group (P=0.03). The experimental group demonstrated a 17.35% increase in average torque whereas the control group demonstrated a 3.68% decrease in average torque. These findings are consistent with other studies demonstrating that the use of grade IV non-thrust mobilization improves strength immediately post-intervention in healthy individuals. The results of this pilot study provide physical therapists with further support for the utilization of manual therapy in conjunction with therapeutic exercise to enhance muscle strength. [ABSTRACT FROM AUTHOR]

The aim of this study was to compare maximal isometric torque and EMG activity of neck flexors and extensors in flexed and extended positions between men and women. Twenty four non-trained young healthy subjects (12 men vs. 12 women) performed maximal isometric neck flexion and extension within 30° around the neutral position in a sitting posture using a modified isokinetic dynamometer. Surface EMG activity of sternocleidomastoid, scalenus, paraspinal and upper trapezius muscles was recorded bilaterally. Men exhibited higher normalized-to-lean body weight torque than women mainly during neck flexion (44%, P<0.001) compared to extension (18%, P<0.05). In addition, torque increased from extended to flexed positions in women only (+17%, P<0.001). This was associated with a decrease in EMG of neck extensors and upper trapezius muscles (from 35% to 20% and from 18% to 7%, P< 0.001, respectively) without changes in agonistic activity of neck flexors with neck position. In contrast, men displayed similar torque and muscle activation level within 30° of range of motion around the neutral position for both directions. These findings demonstrate gender-specific differences in neck function that was probably linked to higher coactivation level in antagonist muscles (neck extensors) and stabilizers (upper trapezius muscles). [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this study was to examine the effects of interelectrode distance (IED) on the absolute and normalized electromyographic (EMG) amplitude and mean power frequency (MPF) versus isokinetic and isometric torque relationships for the biceps brachii muscle. Ten adults [mean±SD age=22.0±3.4 years] performed submaximal to maximal, isokinetic and isometric muscle actions of the dominant forearm flexors. Following determination of isokinetic peak torque (PT) and the isometric maximum voluntary contraction (MVC), the subjects performed randomly ordered, submaximal step muscle actions in 10% increments from 10% to 90% PT and MVC. Surface EMG signals were recorded simultaneously from bipolar electrode arrangements placed over the biceps brachii muscle with IEDs of 20, 40, and 60mm. Absolute and normalized EMG amplitude (μVrms and %max) increased linearly with torque during the isokinetic and isometric muscle actions (r 2 range=0.988–0.998), but there were no significant changes for absolute or normalized EMG MPF (Hz or %max) from 10% to 100% PT and MVC. In some cases, there were significant (p &#60;0.05) differences among the three IED arrangements for absolute EMG amplitude and MPF values, but not for the normalized values. These findings suggested that for the biceps brachii muscle, IEDs between 20 and 60mm resulted in similar patterns for the EMG amplitude or MPF versus dynamic and isometric torque relationships. Furthermore, unlike the absolute EMG amplitude and MPF values, the normalized EMG data were not influenced by changes in IED between 20 and 60mm. Thus, normalized EMG data can be compared among previous studies that have utilized different IED arrangements. [Copyright &y& Elsevier]

This study determined mechanical power during movements specific to maximal walking and running using a non-motorized treadmill in 38 elderly [69.4 (5.0) years] and 50 young [24.3 (3.4) years] men. The mean mechanical power over a period of time covering six steps, during which the belt velocity peaked and then kept almost plateau, was determined as a performance score in each of maximal walking (WP) and running (RP). In terms of the value relative to body mass, the relative difference between the two age groups was greater for RP (61.7%) than for WP (21.4%) or isometric knee extension (34.1%) and flexion torque (43.8%). In the two groups, WP was significantly (P<0.05) correlated to knee extension (r=0.582 for the elderly and r=0.392 for the young) and flexion torque (r=0.524 for the elderly and r=0.574 for the young). Similarly, RP was also significantly (P<0.05) correlated to knee extension (r=0.627 for the elderly and r=0.478 for the young) and flexion torque (r=0.500 for the elderly and r=0.281 for the young). In these relationships, the WP adjusted statistically by thigh muscle torque was similar in the two age groups. However, the corresponding value for RP was significantly higher in the young than in the elderly. The findings here indicate that: (1) the difference between the young and elderly men in mechanical power is greater during maximal running than maximal walking, and (2) although the thigh muscle torque contributes to the power production during the two maximal exercise modes in the two age groups, the RP is greater in the young than in the elderly regardless of the difference in the thigh muscle torque. [ABSTRACT FROM AUTHOR]

The aim of this study was to examine specific and interactional effects of estradiol and progesterone on the time-to-fatigue of eccentrically contracted plantarflexor muscles and on the percent of plantarflexor isometric torque remaining immediately after an eccentric contraction (EC) protocol. Ovariectomized 6- to 8-week-old C57BL/6 mice were implanted with 21-day 0.05 mg-placebo, 0.05 mg-17-β estradiol (OE),15 mg-progesterone (OP), or estradiol and progesterone pellets (OEP). On the 16th day of hormone treatment, the isometric torque of the left plantarflexor muscles was measured. The left plantarflexor muscles then underwent 1 set of 150 ECs followed by 2 immediate post-EC isometric torque measurements. A group of ovarian-intact female mice of a similar age underwent the same isometric torque measurements and EC protocol. Plantarflexor muscle fatigue during ECs took 30%-41 % longer to occur in the OP group (n = 9) than it did in the intact (n = 8, P = 0.02), OC (n =11, P = 0.003), and OEP (n = 9, P = 0.007) groups. Peak active isometric torque had decreased immediately after ECs at 2 time points (M1 and M2). The OP group exhibited the greatest percent of isometric torque remaining immediately after ECs (M1, P = 0.03; M2, P = 0.04). These findings suggest that progesterone reduces muscle fatigue in response to ECs and that this progesterone effect is blunted when estradiol also is present. Therefore, ovarian hormone status may need to be considered when evaluating a response to physical activities, especially those activities involving ECs. [ABSTRACT FROM AUTHOR]

The article highlights the link between kinematic and dynamic parameters of task related to elbow flexion-extension tasks to investigate the possible discomfort evaluation laws. The study shows that intermediate elbow flexion has a higher effort perception. The study emphasizes that joint position and effort level have a significant effect on the subjective effort perception for a simple task.