首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
In this study, we examined the long-term reductions in maximal isometric force (MIF) caused by a protocol of repeated maximal isometric contractions at long muscle length. Furthermore, we wished to ascertain whether the reductions in MIF are dependent on muscle length--that is, are the reductions in MIF more pronounced when the muscle contracts at a short length. The MIF of the elbow flexors of seven young male volunteers was measured at five different elbow angles between 50 degrees and 160 degrees. On a separate day, the participants performed 50 maximal voluntary isometric muscle contractions with the elbow flexors at a lengthened position; that is, with the shoulder hyperextended at 45 degrees and the elbow joint fixed at 140 degrees. Following this exercise, the MIF at the five elbow angles, range of motion, muscle soreness and plasma creatine kinase activity were measured at 24 h intervals for 4 days. On day 1, the decline in MIF was higher at the more acute elbow angles of 50 degrees (42 +/- 8%) and 70 degrees (39 +/- 8%; both P<0.01) than at 90 degrees (26 +/- 4%) and 140 degrees (16 +/- 3%; both P<0.01). No significant reduction in MIF was evident at an elbow angle of 160 degrees. Maximal isometric force at an elbow angle of 140 degrees was fully restored on day 3, whereas at an angle of 50 degrees it remained depressed for the 4 day observation period. Restoration of MIF was a function of the elbow angle, with force recovery being less at the smaller angles. The range of motion was decreased by 14 +/- 2 degrees on day 1 (P<0.01) and did not return to baseline values by day 4. Muscle soreness ratings remained significantly elevated for the 4 day period. Serum creatine kinase peaked on day 1 (522 +/- 129 IU, P<0.01) and decreased thereafter. We conclude that the disproportionate decrease in MIF at the small elbow angles and the length-specific recovery in MIF after repeated maximal isometric contractions at long muscle length may be explained by the presence of overstretched sarcomeres that increased in series compliance of the muscle, therefore causing a rightward shift of the force-length relationship.  相似文献   

2.
This study compared knee angle-specific neuromuscular adaptations after two low-volume isometric leg press complex training programmes performed at different muscle lengths. Fifteen young males were divided into two groups and trained three times per week for 6 weeks. One group (n?=?8) performed 5–7 sets of 3 s maximum isometric leg press exercise, with 4?min recovery, with knee angle at 85°?±?2° (longer muscle-tendon unit length; L-MTU). The other group (n?=?7) performed the same isometric training at a knee angle of 145°?±?2° (180°?=?full extension; shorter muscle-tendon unit length; S-MTU). During the recovery after each set of isometric exercise, participants performed two CMJ every minute, as a form of complex training. Maximum isometric force (MIF) and rate of force development (RFD) were measured over a wide range of knee angles. Countermovement jump (CMJ) performance and maximum half-squat strength (1RM) were also assessed. Training at S-MTU induced a large increase of MIF (22–58%, p?p?p?=?0.001). In contrast, training at L-MTU, resulted in a moderate and similar (≈12.3%, p?=?0.028) improvement of force at all knee angles. CMJ performance and 1RM were equally increased in both groups after training by 10.4%?±?8.3% and 7.8%?±?4.7% (p?相似文献   

3.
Upper-body dynamic and isometric maximum strength are essential components for success in Brazilian jiu-jitsu (BJJ). This study was aimed at analysing strength parameters in the elbow flexor and extensor muscles of BJJ practitioners. Participants (n = 28) performed maximum isometric contractions of elbow flexors and extensors to determine peak torque (PT), rate of force development (RFD), and the torque–angle (T–A) relationship at elbow angles of 45°, 60°, 75°, 90°, 105°, and 120°. Additionally, concentric and eccentric PTs were measured at 1.04 rad·s-1. Student t-test and ANOVA were performed using α = 0.05. Elbow flexors were stronger isometrically (P < 0.001, ES = 1.23) but weaker concentrically (P < 0.05, ES = 0.54) than extensor muscles, possibly because of the extensive grip disputes and pushing of opponents in BJJ. The T–A relationship had an inverted “U”-shape. Torque differences across elbow angles were moderate (ES = 0.62) for the extensor and large (ES = 0.92) for the flexor muscles. Isometric torque was greatest for elbow angles of 105° and 75° and smallest for 45° and 120° for extensor and flexor muscles, respectively. Elbow flexors had a greater RFD than extensors, regardless of elbow angle. The present study provides comprehensive results for elbow muscle strength in BJJ practitioners.  相似文献   

4.
A single bout of eccentric exercise induces a protective adaptation against damage from a repeated bout. The aim of this study was to determine whether this repeated bout effect is due to a change in the length–tension relationship. Twelve individuals performed an initial bout of six sets of 10 eccentric quadriceps contractions and then performed a repeated bout 2 weeks later. Eccentric contractions were performed on an isokinetic dynamometer at 1.04 rad?·?s?1 with a target intensity of 90% of isometric strength at 70° of knee flexion. Isometric strength and pain were recorded before and after both eccentric bouts and on each of the next 3 days. Isometric strength was tested at 30°, 50°, 70°, 90° and 110° of knee flexion. On the days following the initial bout, there was a significant loss of isometric strength at all knee flexion angles except 110° (bout×angle: P?<0.01). On day 2, strength averaged 86% of baseline for 30–90° and 102% of baseline for 110°. Strength loss and pain after the initial bout was contrasted by minimal changes after the repeated bout (pain: P?<0.001; strength: P?<0.01). The repeated bout effect was associated with a rightward shift in the length–tension curve; before the repeated bout, isometric strength was 6.8% lower at 30° and 13.6% higher at 110° compared with values before the initial bout (bout×angle: P?<0.05). Assuming that torque production at 110° occurs on the descending limb of the length–tension curve, the increase in torque at 110° may be explained by a longitudinal addition of sarcomeres. The addition of sarcomeres would limit sarcomere strain for subsequent eccentric contractions and may explain the repeated bout effect observed here.  相似文献   

5.
Abstract

In this study, we wished to determine whether a warm-up exercise consisting of 100 submaximal concentric contractions would attenuate delayed-onset muscle soreness and decreases in muscle strength associated with eccentric exercise-induced muscle damage. Ten male students performed two bouts of an elbow flexor exercise consisting of 12 maximal eccentric contractions with a warm-up exercise for one arm (warm-up) and without warm-up for the other arm (control) in a randomized, counterbalanced order separated by 4 weeks. Muscle temperature of the biceps brachii prior to the exercise was compared between the arms, and muscle activity of the biceps brachii during the exercise was assessed by surface integral electromyogram (iEMG). Changes in visual analogue scale for muscle soreness and maximal voluntary isometric contraction strength (MVC) of the elbow flexors were assessed before, immediately after, and every 24 h for 5 days following exercise, and compared between the warm-up and control conditions by a two-way repeated-measures analysis of variance. The pre-exercise biceps brachii muscle temperature was significantly (P<0.01) higher for the warm-up (35.8±0.2°C) than the control condition (34.4±0.2°C), but no significant differences in iEMG and torque produced during exercise were evident between conditions. Changes in muscle soreness and MVC were not significantly different between conditions, although these variables showed significant (P<0.05) changes over time. It was concluded that the warm-up exercise was not effective in mitigating delayed-onset muscle soreness and loss of muscle strength following maximal eccentric exercise.  相似文献   

6.
Abstract

The temporal structure, or complexity, of muscle torque output reflects the adaptability of motor control to changes in task demands. This complexity is reduced by neuromuscular fatigue during intermittent isometric contractions. We tested the hypothesis that sustained fatiguing isometric contractions would result in a similar loss of complexity. To that end, nine healthy participants performed, on separate days, sustained isometric contractions of the knee extensors at 20% MVC to task failure and at 100% MVC for 60?s. Torque and surface EMG signals were sampled continuously. Complexity and fractal scaling were quantified by calculating approximate entropy (ApEn) and the detrended fluctuation analysis (DFA) α scaling exponent. Global, central and peripheral fatigue were quantified using maximal voluntary contractions (MVCs) with femoral nerve stimulation. Fatigue reduced the complexity of both submaximal (ApEn from 1.02?±?0.06 to 0.41?±?0.04, P?<?0.05) and maximal contractions (ApEn from 0.34?±?0.05 to 0.26?±?0.04, P?<?0.05; DFA α from 1.41?±?0.04 to 1.52?±?0.03, P?<?0.05). The losses of complexity were accompanied by significant global, central and peripheral fatigue (all P?<?0.05). These results demonstrate that a fatigue-induced loss of torque complexity is evident not only during fatiguing intermittent isometric contractions, but also during sustained fatiguing contractions.  相似文献   

7.
It is currently unclear how football participation affects knee-joint muscle balance, which is widely considered a risk factor for hamstrings injury. This study compared the angle-specific functional hamstring-to-quadriceps (H:Q) ratio (hamstrings eccentric torque as a ratio of quadriceps concentric torque at the same knee-joint angle) of football players with recreationally active controls. Ten male footballers and 14 controls performed maximal voluntary isometric and isovelocity concentric and eccentric contractions (60, 240 and 400° s?1) of the knee extensors and flexors. Gaussian fitting to the raw torque values was used to interpolate torque values for knee-joint angles of 100–160° (60° s?1), 105–160° (240° s?1) and 115–145° (400° s?1). The angle-specific functional H:Q ratio was calculated from the knee flexors eccentric and knee extensors concentric torque at the same velocity and angle. No differences were found for the angle-specific functional H:Q ratio between groups, at any velocity. Quadriceps and hamstrings strength relative to body mass of footballers and controls was similar for all velocities, except concentric knee flexor strength at 400° s?1 (footballers +40%; P < 0.01). In previously uninjured football players, there was no intrinsic muscle imbalance and therefore the high rate of hamstring injuries seen in this sport may be due to other risk factors and/or simply regular exposure to a high-risk activity.  相似文献   

8.
This investigation examined effects of two exercise modes (barbell, BB; bodyweight suspension, BWS) on muscle activation, resistance load, and fatigue. During session one, nine resistance-trained males completed an elbow flexion one-repetition maximum (1RM). During sessions two and three, subjects completed standing biceps curls to fatigue at 70% 1RM utilizing a randomized exercise mode. Surface electromyography (sEMG) recorded muscle activation of the biceps brachii, triceps brachii, anterior deltoid, posterior deltoid, rectus abdominis, and erector spinae. BWS resistance load was measured using a force transducer. Standing maximal voluntary isometric contractions of the elbow flexors recorded at 90° were used to determine the isometric force decrement and rate of fatigue (ROF) during exercise. sEMG and resistance load data were divided into 25% contraction duration bins throughout the concentric phase. BWS resulted in a 67.7?±?7.4% decline in resistance load throughout the concentric phase (p?≤?0.05). As a result, BB elicited higher mean resistance loads (31.4?±?4.0?kg) and biceps brachii sEMG (84.7?±?27.8% maximal voluntary isometric contractions, MVIC) compared with BWS (20.4?±?3.4?kg, 63.4?±?21.6% MVIC). No difference in rectus abdominis or erector spinae sEMG was detected between exercise modes. Isometric force decrement was greater during BWS (?21.7?±?7.0?kg) compared with BB (?14.9?±?4.7?kg); however, BB (?3.0?±?0.8?kg/set) resulted in a steeper decline in ROF compared with BWS (?1.7?±?0.6?kg/set). The variable resistance loading and greater isometric force decrement observed suggest that select BWS exercises may resemble variable resistance exercise more than previously considered.  相似文献   

9.
Abstract

This study was undertaken to examine the acute effect of interferential current on mechanical pain threshold and isometric peak torque after delayed onset muscle soreness induction in human hamstrings. Forty-one physically active healthy male volunteers aged 18?33 years were randomly assigned to one of two experimental groups: interferential current group (n = 21) or placebo group (n = 20). Both groups performed a bout of 100 isokinetic eccentric maximal voluntary contractions (10 sets of 10 repetitions) at an angular velocity of 1.05 rad · s?1 (60° · s?1) to induce muscle soreness. On the next day, volunteers received either an interferential current or a placebo application. Treatment was applied for 30 minutes (4 kHz frequency; 125 μs pulse duration; 80?150 Hz bursts). Mechanical pain threshold and isometric peak torque were measured at four different time intervals: prior to induction of muscle soreness, immediately following muscle soreness induction, on the next day after muscle soreness induction, and immediately after the interferential current and placebo application. Both groups showed a reduction in isometric torque (P < 0.001) and pain threshold (P < 0.001) after the eccentric exercise. After treatment, only the interferential current group showed a significant increase in pain threshold (P = 0.002) with no changes in isometric torque. The results indicate that interferential current was effective in increasing hamstrings mechanical pain threshold after eccentric exercise, with no effect on isometric peak torque after treatment.  相似文献   

10.
The aim of the present study was to examine the effects of viscoelastic properties of human tendon structures during stretch?–?shortening cycle exercise. The elongation of tendon and aponeurosis of the medial gastrocnemius muscle of 26 participants was measured by ultrasonography while they performed ramp isometric plantar flexion up to the voluntary maximum, followed by a ramp relaxation. The relationship between estimated muscle force and tendon elongation during the ascending phase was fitted to a linear regression, the slope of which was defined as stiffness. The percentage of the area within the muscle force?–?tendon elongation loop relative to the area beneath the curve during the ascending phase was defined as hysteresis. In addition, maximal voluntary concentric contractions at 2.09 and 3.14 rad?·?s?1 with and without prior eccentric contractions were performed. The difference in the concentric torque at equivalent joint angles with and without prior eccentric contractions (i.e. pre-stretch augmentation) was negatively correlated with stiffness (P <?0.05) and hysteresis (P <?0.05). Furthermore, there was a higher correlation between the pre-stretch augmentation and the viscoelastic properties index – that is, the sum of normalized score values of stiffness and hysteresis (P <?0.01) – than with either stiffness or hysteresis alone. The results of this study suggest that performance during stretch?–?shortening cycle exercise is significantly affected by the viscoelastic properties of the tendon structures.  相似文献   

11.
Abstract

Ten healthy males and ten healthy females aged 21.5 ± 3.2 years (mean ± s) participated in the study, which was designed to evaluate the effectiveness of sensory level-high volt pulsed electrical current (HVPC) on delayed-onset muscle soreness (DOMS). Arm discomfort, elbow extension range of motion and isometric elbow flexion strength were obtained as baseline measurements. Delayed-onset muscle soreness was induced in the participants' dominant or non-dominant arm using two sets of 20 maximal eccentric elbow flexion contractions. After the induction of DOMS, the participants were randomly divided into an experimental condition (HVPC) or a placebo condition. The experimental condition consisted of 20 min of HVPC immediately after the induction of DOMS, and 20 min every 24 h for three consecutive days thereafter. The participants in the placebo condition received an intervention similar in design; however, no electrical current was administered. Baseline measurements were reevaluated at 24, 48, 72 and 96 h after the induction of DOMS. Three weeks later, the participants returned and the protocol was repeated on the contralateral limb, using the opposite intervention (HVPC or placebo). Repeated-measures analysis of variance revealed a significant increase in overall arm discomfort, decrease in elbow extension and decrease in isometric strength for both conditions over time. No significant main effect of treatment, or time-by-treatment interaction, was found for the HVPC condition when compared with the placebo condition for any variable. Sensory-level HVPC, as utilized in our application, was ineffective in reducing the measured variables associated with DOMS.  相似文献   

12.
The maximal isometric force (MIF) of a muscle is directly related to its cross‐sectional area (CSA). Strength training produces an increase in muscular force while muscular hypertrophy becomes appreciable at a later time; in asymmetric sports, training causes significant increases in force and muscular mass of the dominant limb of the athlete. The aim of this study was to analyse the differences in muscular force and trophism between the dominant and non‐dominant forearms in fencers and in controls.

The data of 17 male distance runners (age 21.4±2.4 years, body mass 74.0±5.0 kg, height 180 ± 6 cm) were compared with those of 58 male fencers (age 23.0 ± 6.7 years, body mass 71.9±9.3 kg, height 178 ± 7 cm) drawn from the ranking lists of the National Fencing Committee. They trained for a mean of 11.4±6.0 (range 2–36) years, commencing at 10.7 ± 4.5 years of age.

Cross‐sectional area (muscle plus bone) was estimated in the dominant and non‐dominant forearm using a simplified anthropometric method. Maximal isometric force was determined using a mechanical handgrip dynamometer. The differences in CSA and isometric force between the two limbs and between fencers and controls were tested using paired and unpaired Student's i‐tests, respectively. Significant differences in CSA and maximal force were observed between the dominant and non‐dominant forearm in fencers (both P<0.001) and in controls (P<0.005 and P<0.001, respectively). The fencers showed a greater CSA (P<0.001) and force (P< 0.001) in the dominant forearm compared with the control group. Furthermore, the differences between the dominant and non‐dominant limb of the fencers were significantly greater than the differences between the dominant and non‐dominant limb of the controls (P<0.001 for CSA and P<0.05 for force). No significant differences in stress ratio (force/CSA) were obtained in either group.

The results of this study suggest that asymmetric sports training at submaximal intensities produces significant asymmetries in force and CSA which are independent of technical level and years of training. Despite this, the force/CSA ratio is constant and independent of training.  相似文献   

13.
Abstract

The aims of this study were to examine age and sex differences in elbow extensor and flexor anatomical muscle cross-sectional area (mCSA) measured by magnetic resonance imaging (MRI) and the location of maximal mCSA as a percentage of the distance from the distal to the proximal end of the humerus. Ninety-five individuals spread across the age groups 9 – 10 years, 16 – 17 years and 21 years participated in the study. Muscle cross-sectional area derived from the manual MRI tracing proved to be highly reliable in terms of limits of agreement (?2.5 to 1.5 cm2) and the intraclass correlation coefficient (ICC = 0.998). A sex-by-age group analysis of variance revealed significant effects (P < 0.01) of sex, group and a sex-by-group interaction, the latter reflecting a greater increase in males than females of upper arm mCSA from childhood to adulthood. Extensor mCSA was more proximal (55 ± 6%) than that of the flexors (28 ± 6%). A significant effect (P < 0.01) of group was found for location of maximal extensor mCSA, reflecting its more distal position with increasing age. Measurements of muscle size should be made at the individually determined position of maximal mCSA if interpreting data collected during growth and maturation, especially if the muscle group of interest is the elbow extensors and if different age groups are being monitored.  相似文献   

14.
Abstract

The purpose of this study was to investigate the eccentric torque–velocity and power–velocity relationships of the elbow flexors. Forty recreationally trained individuals (20 men, 20 women) performed maximal eccentric actions at each of five different velocities (1.04 rad · s?1, 2.09 rad · s?1, 3.14 rad · s?1, 4.18 rad · s?1, and 5.23 rad · s?1, in random order) and maximal isometric actions on a Biodex isokinetic dynamometer. A 2×6 (sex×velocity) mixed-factor repeated-measures analysis of variance (ANOVA) was used to assess peak elbow flexor torque during the eccentric and isometric actions. There was no interaction, but there were significant main effects for sex and velocity. Pairwise comparisons demonstrated that values for men were significantly (P<0.05) higher than those for women at all speeds. Furthermore, torques for both sexes were significantly less at 3.14 rad · s?1 (men: 103.94±28.28 N · m; women: 49.24±11.69 N · m) than at 4.18 rad · s?1 (men: 106.39±30.23 N · m; women: 52.77±11.31 N · m) and 5.23 rad · s?1 (men: 108.75±28.59 N · m; women: 53.3±11.67 N · m), while isometric torque was significantly less than at all other speeds (men: 98.66±28.0 N · m; women: 45.25±11.15 N · m). A 2×5 (sex×velocity) mixed-factor repeated-measures ANOVA was used to assess peak eccentric elbow flexor power. There were significant main effects for sex and velocity. Pairwise comparisons demonstrated that values for men were significantly higher than those for women at all speeds. Pairwise comparisons for velocity indicated that peak eccentric power increased across all speeds from 1.04 rad · s?1 (men: 110.44±32.56 W; women 54.36±13.05 W) to 5.23 rad · s?1 (men: 569.46±149.73 W; women: 279.10±61.10 W). These results demonstrate that an increase in velocity had little or no effect on eccentric elbow flexor torque, while eccentric elbow flexor power increased significantly with increases in velocity.  相似文献   

15.
The length-tension relationship of muscle contraction is well documented in adults. However, research on this relationship in children has been limited. The aim of this study was to compare differences in the torque-joint angle relationship of the quadriceps muscle in children and adults. Eight boys aged 8-10 years and eight men aged 20-26 years performed two maximal voluntary isometric contractions at six knee joint angles (20°, 40°, 60°, 80°, 90°, 100°). The mean of the two trials was used as the performance measure. Both groups demonstrated an expected increase in relative torque as the joint angle increased (P ? 0.05). The men produced significantly greater relative torque at 20°, 40° and 60° knee flexion (P ? 0.05). The percentage of maximal torque at these angles for the men and boys respectively were: 35.2 - 4.3 vs 15.2 - 12%, 63.6 - 9.1 vs 51.8 - 16.8% and 93.6 - 6.5 vs 84.4 - 14.4%. There were no group differences at 80° or 90°. Peak torque was attained at 80° in men, but decreased significantly (P ? 0.05) at 90° and 100°. For boys, peak torque was attained at joint angles of 80° and 90°. The reduction in peak torque at 100° was not statistically significant, but the relative torque at this angle was lower in men than in boys (77.9 - 13.7 vs 87.1 - 10.4%; P ? 0.05). In conclusion, the relationship between torque and joint angle appears to be affected by age.  相似文献   

16.
Abstract

The objective of this study was to determine whether sprint performance is related to the mechanical (elongation – force relationship of the tendon and aponeurosis, muscle strength) and morphological (fascicle length, pennation angle, muscle thickness) properties of the quadriceps femoris and triceps surae muscle – tendon units. Two groups of sprinters (slow, n = 11; fast, n = 17) performed maximal isometric knee extension and plantar flexion contractions on a dynamometer at 11 different muscle – tendon unit lengths. Elongation of the tendon and aponeurosis of the gastrocnemius medialis and the vastus lateralis was measured using ultrasonography. We observed no significant differences in maximal joint moments at the ankle and knee joints or morphological properties of the gastrocnemius medialis and vastus lateralis between groups (P > 0.05). The fast group exhibited greater elongation of the vastus lateralis tendon and aponeurosis at a given tendon force, and greater maximal elongation of the vastus lateralis tendon and aponeurosis during maximum voluntary contraction (P < 0.05). Furthermore, maximal elongation of the vastus lateralis tendon and aponeurosis showed a significant correlation with 100-m sprint times (r = ?0.567, P = 0.003). For the elongation – force relationship at the gastrocnemius medialis tendon and aponeurosis, the two groups recorded similar values. It is suggested that the greater elongation of the vastus lateralis tendon and aponeurosis of the fast group benefits energy storage and return as well as the shortening velocity of the muscle – tendon unit.  相似文献   

17.
Abstract

The present investigation verified that strength is improved by a training programme consisting of repetitions of maximal isometric voluntary co-contractions without increasing co-activations during contractions against external resistances. Ten participants performed 12 training sessions (four sets of 6 × 4 second maximal isometric co-contraction of the elbow flexor and extensors, 3 days a week for 4 weeks). Surface electromyograms of triceps and biceps brachii were collected during maximal voluntary isometric elbow flexion and extension against a force transducer. Maximal voluntary isometric force increased significantly after training, by 13.8 ± 6.0% (extension) and 9.6 ± 9.5% (flexion), but the observed increases in EMG of agonist muscles during maximal voluntary contraction were not significant. No significant changes in the levels of co-activation of the elbow flexors and extensors were observed. No significant change was observed for all the parameters in a control group of ten participants. These results indicated that the strength improvements after co-contraction training occur without increases in co-activation level.  相似文献   

18.
Abstract

The purpose of the present study was to examine whether static and dynamic balance control are related to neuromuscular function and ageing. For this purpose, we constructed a new dynamic balance measurement system that simulates natural falling. Ten young (age 21–31 years) and 20 elderly (age 60–70 years) men participated in the experiment. Maximal isometric torque (MVC) and activation level were measured from the quadriceps and plantar flexor muscles. The H-reflex, V-wave, and maximal M-wave were measured from the soleus muscle. In dynamic balance control, anterior-posterior centre-of-pressure swaying was 74±8.1 mm in the young men and 91.5±19.4 mm in the elderly men (P<0.05), whereas in the static condition there were no significant differences between the two groups. Knee extension MVC (young: 181±42 N·m; elderly: 135±39 N·m; P<0.01), torque after 500 ms (young: 147±36 N·m; elderly: 108±39 N·m; P<0.05), and activation level (young: 96.2±0.8%; elderly: 93.8±2.1%; P<0.01) were higher in the young than the elderly men; no differences were observed in plantar flexion. The amount of re-stabilization after a sudden disturbance seems to be an age-related phenomenon, which is seen as a connection between balance control and rapid force production.  相似文献   

19.
Abstract

The main aim of this study was to compare the reliability of percutaneous electrical stimulation over the muscle (MES) and electrical stimulation over the nerve (NES) to assess quadriceps muscle voluntary activation and muscle contractile properties. A secondary aim was to determine whether MES detects the fatigue induced by prolonged exercise in the heat. For the first purpose, eight participants performed on three non-consecutive days: quadriceps maximal voluntary contractions (MVC) with superimposed electrical stimulation to assess voluntary activation, and electrically evoked contractions to assess peak force (PEVO), using NES (ball-shaped cathode) or MES (adhesive electrodes). For the second purpose, the same participants pedalled for 2 h at 60% VO2max in a 36°C environment. Quadriceps maximal voluntary contractions, voluntary activation, and PEVO were measured before and just after the completion of exercise using MES. Voluntary activation assessed with MES presented lower intra-day (1.3±0.2 vs. 2.5±0.5%) and inter-day (1.7±0.3 vs. 2.9 ±0.4%) coefficients of variation than with NES. PEVO had lower intra-day and inter-day coefficients of variation (5.6±1.0 vs. 17.0±3.3%) and higher intraclass correlation values (ICC 0.95 vs. 0.85) when using MES than with NES either when stimulating at 20 or 80 Hz. Prolonged exercise in the heat reduced MVC (11±2%) and quadriceps muscle voluntary activation (5.2±0.5%) from pre-exercise values (P<0.05), as previously found. PEVO was unaffected by exercise in the heat. In conclusion, MES is more reliable than NES to assess quadriceps muscle voluntary activation and PEVO. In addition, MES readily detects the reduction in voluntary activation induced by prolonged exercise in the heat.  相似文献   

20.
Abstract

The purpose of this study was to examine the effect of fatiguing exercise on sex-related differences in the function of hamstring and quadriceps muscles at several angular velocities and joint angles. Physically active participants (50 male: 28.7?±?4.5y, 1.82?±?0.07 m, 82.3?±?6.87?kg; 50 female: 27.0?±?5.8y, 1.61?±?0.08 m, 68.75?±?9.24?kg) carried out an isokinetic assessment to determine concentric and eccentric torques during knee extension and flexion actions at three different angular velocities (60/180/300°/s). The H/QFUNCT was calculated using peak torque (PT) values at 3 different joint-angle-specific (15°, 30° and 45° of knee flexion). A repeated measures analysis of variance (ANOVA) was used to compare within group results. Between group comparisons of sex-related differences were assessed by independent T-tests. Fatiguing exercise in males resulted in a decrease in H/QFUNCT ratios for each angle of knee flexion at both 60°/s and 300°/s angular velocities (p?<?0.05). In females, significant decreases in H/QFUNCT ratios were observed following fatiguing exercise for each angle of knee flexion and angular velocity (p?<?0.01). Significant differences in H/QFUNCT ratios following fatiguing exercise were evident between males and females at each joint angle and angular velocity (p?<?0.01). These findings indicate sex related differences in H/QFUNCT ratios following fatiguing exercise. Females have greater reductions in torque and H/QFUNCT ratios following fatigue than their male counterparts. This potentially exposes females to higher risks of injury, particularly when fatigued. Practitioners should attend to the imbalance in fatigue resistance of hamstring and quadriceps function, particularly in female athletes.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号