Repeated exercise stress impairs volitional but not magnetically evoked electromechanical delay of the knee flexors

The effects of serial episodes of fatigue and recovery on volitional and magnetically evoked neuromuscular performance of the knee flexors were assessed in 20 female soccer players during: (i) an intervention comprising 4 × 35 s maximal static exercise, and (ii) a control condition. Volitional peak force was impaired progressively (-16% vs. baseline: 235.3 ± 54.7 to 198.1 ± 38.5 N) by the fatiguing exercise and recovered to within -97% of baseline values following 6 min of rest. Evoked peak twitch force was diminished subsequent to the fourth episode of exercise (23.3%: 21.4 ± 13.8 vs. 16.4 ± 14.6 N) and remained impaired at this level throughout the recovery. Impairment of volitional electromechanical delay performance following the first episode of exercise (25.5%: 55.3 ± 11.9 vs. 69.5 ± 24.5 ms) contrasted with concurrent improvement (10.0%: 24.5 ± 4.7 vs. 22.1 ± 5.0 ms) in evoked electromechanical delay (P < 0.05), and this increased disparity between evoked and volitional electromechanical delay remained during subsequent periods of intervention and recovery. The fatiguing exercise provoked substantial impairments to volitional strength and volitional electromechanical delay that showed differential patterns of recovery. However, improved evoked electromechanical delay performance might identify a dormant capability for optimal muscle responses during acute stressful exercise and an improved capacity to maintain dynamic joint stability during critical episodes of loading.     

Eccentric exercise-induced muscle damage dissociates the lactate and gas exchange thresholds

We tested the hypothesis that exercise-induced muscle damage would increase the ventilatory (V(E)) response to incremental/ramp cycle exercise (lower the gas exchange threshold) without altering the blood lactate profile, thereby dissociating the gas exchange and lactate thresholds. Ten physically active men completed maximal incremental cycle tests before (pre) and 48 h after (post) performing eccentric exercise comprising 100 squats. Pulmonary gas exchange was measured breath-by-breath and fingertip blood sampled at 1-min intervals for determination of blood lactate concentration. The gas exchange threshold occurred at a lower work rate (pre: 136 ± 27 W; post: 105 ± 19 W; P < 0.05) and oxygen uptake (VO(2)) (pre: 1.58 ± 0.26 litres · min(-1); post: 1.41 ± 0.14 litres · min(-1); P < 0.05) after eccentric exercise. However, the lactate threshold occurred at a similar work rate (pre: 161 ± 19 W; post: 158 ± 22 W; P > 0.05) and VO(2) (pre: 1.90 ± 0.20 litres · min(-1); post: 1.88 ± 0.15 litres · min(-1); P > 0.05) after eccentric exercise. These findings demonstrate that exercise-induced muscle damage dissociates the V(E) response to incremental/ramp exercise from the blood lactate response, indicating that V(E) may be controlled by additional or altered neurogenic stimuli following eccentric exercise. Thus, due consideration of prior eccentric exercise should be made when using the gas exchange threshold to provide a non-invasive estimation of the lactate threshold.     

The effect of exercise-induced muscle damage on isometric and dynamic knee extensor strength and vertical jump performance

In this study, we assessed the effect of exercise-induced muscle damage on knee extensor muscle strength during isometric, concentric and eccentric actions at 1.57 rad · s -1 and vertical jump performance under conditions of squat jump, countermovement jump and drop jump. The eight participants (5 males, 3 females) were aged 29.5 - 7.1 years (mean - s ). These variables, together with plasma creatine kinase (CK), were measured before, 1 h after and 1, 2, 3, 4 and 7 days after a bout of muscle damaging exercise: 100 barbell squats (10 sets 2 10 repetitions at 70% body mass load). Strength was reduced for 4 days ( P ? 0.05) but no significant differences ( P > 0.05) were apparent in the magnitude or rate of recovery of strength between isometric, concentric and eccentric muscle actions. The overall decline in vertical jump performance was dependent on jump method: squat jump performance was affected to a greater extent than countermovement (91.6 - 1.1% vs 95.2 - 1.3% of pre-exercise values, P ? 0.05) and drop jump (95.2 - 1.4%, P ? 0.05) performance. Creatine kinase was elevated ( P ? 0.05) above baseline 1 h after exercise, peaked on day 1 and remained significantly elevated on days 2 and 3. Strength loss after exercise-induced muscle damage was independent of the muscle action being performed. However, the impairment of muscle function was attenuated when the stretch-shortening cycle was used in vertical jumping performance.     

The effect of exercise-induced muscle damage on isometric and dynamic knee extensor strength and vertical jump performance

In this study, we assessed the effect of exercise-induced muscle damage on knee extensor muscle strength during isometric, concentric and eccentric actions at 1.57 rad x s(-1) and vertical jump performance under conditions of squat jump, countermovement jump and drop jump. The eight participants (5 males, 3 females) were aged 29.5+/-7.1 years (mean +/- s). These variables, together with plasma creatine kinase (CK), were measured before, 1 h after and 1, 2, 3, 4 and 7 days after a bout of muscle damaging exercise: 100 barbell squats (10 sets x 10 repetitions at 70% body mass load). Strength was reduced for 4 days (P< 0.05) but no significant differences (P> 0.05) were apparent in the magnitude or rate of recovery of strength between isometric, concentric and eccentric muscle actions. The overall decline in vertical jump performance was dependent on jump method: squat jump performance was affected to a greater extent than countermovement (91.6+/-1.1% vs 95.2+/-1.3% of pre-exercise values, P< 0.05) and drop jump (95.2+/-1.4%, P< 0.05) performance. Creatine kinase was elevated (P < 0.05) above baseline 1 h after exercise, peaked on day 1 and remained significantly elevated on days 2 and 3. Strength loss after exercise-induced muscle damage was independent of the muscle action being performed. However, the impairment of muscle function was attenuated when the stretch-shortening cycle was used in vertical jumping performance.     

Effects of cold water immersion on the symptoms of exercise-induced muscle damage.

Cryotherapy is an effective treatment for acute sports injury to soft tissue, although the effect of cryotherapy on exercise-induced muscle damage is unclear. The aim of this study was to assess the effects of cold water immersion on the symptoms of exercise-induced muscle damage following strenuous eccentric exercise. After performing a bout of damage-inducing eccentric exercise (eight sets of five maximal reciprocal contractions at 0.58 rad x s(-1)) of the elbow flexors on an isokinetic dynamometer, 15 females aged 22.0+/-2.0 years (mean +/- s) were allocated to a control group (no treatment, n = 7) or a cryotherapy group (n = 8). Subjects in the cryotherapy group immersed their exercised arm in cold water (15 degrees C) for 15 min immediately after eccentric exercise and then every 12 h for 15 min for a total of seven sessions. Muscle tenderness, plasma creatine kinase activity, relaxed elbow angle, isometric strength and swelling (upper arm circumference) were measured immediately before and for 3 days after eccentric exercise. Analysis of variance revealed significant (P < 0.05) main effects for time for all variables, with increases in muscle tenderness, creatine kinase activity and upper arm circumference, and decreases in isometric strength and relaxed elbow angle. There were significant interactions (P<0.05) of group x time for relaxed elbow angle and creatine kinase activity. Relaxed elbow angle was greater and creatine kinase activity lower for the cryotherapy group than the controls on days 2 and 3 following the eccentric exercise. We conclude that although cold water immersion may reduce muscle stiffness and the amount of post-exercise damage after strenuous eccentric activity, there appears to be no effect on the perception of tenderness and strength loss, which is characteristic after this form of activity.     

Maximal-intensity isometric and dynamic exercise performance after eccentric muscle actions

A well-documented observation after eccentric exercise is a reduction in maximal voluntary force. However, little is known about the ability to maintain maximal isometric force or generate and maintain dynamic peak power. These aspects of muscle function were studied in seven participants (5 males, 2 females). Knee extensor isometric strength and rate of fatigue were assessed by a sustained 60 s maximal voluntary contraction at 80 degrees and 40 degrees knee flexion, corresponding to an optimal and a shortened muscle length, respectively. Dynamic peak power and rate of fatigue were assessed during a 30 s Wingate cycle test. Plasma creatine kinase was measured from a fingertip blood sample. These variables were measured before, 1 h after and 1, 2, 3 and 7 days after 100 repetitions of the eccentric phase of the barbell squat exercise (10 sets x 10 reps at 80% concentric one-repetition maximum). Eccentric exercise resulted in elevations in creatine kinase activity above baseline (274+/-109 U x l(-1); mean +/- s(x)) after 1 h (506+/-116 U x l(-1), P < 0.05) and 1 day (808+/-117 U x l(-1), P < 0.05). Isometric strength was reduced (P < 0.05) for 7 days (35% at 1 h, 5% at day 7) and the rate of fatigue was lower (P < 0.05) for 3 days at 80 degrees and for 1 day at 40 degrees. Wingate peak power was reduced to a lesser extent (P < 0.05) than isometric strength at 1 h (13%) and, although the time course of recovery was equal, the two variables differed in their pattern of recovery. Eccentrically exercised muscle was characterized by an inability to generate high force and power, but an improved ability to maintain force and power. Such functional outcomes are consistent with the proposition that type II fibres are selectively recruited or damaged during eccentric exercise.     

Effects of exercise-induced muscle damage on resting metabolic rate,sub-maximal running and post-exercise oxygen consumption

Abstract

Exercise-induced muscle damage (EIMD), described as the acute weakness of the musculature after unaccustomed eccentric exercise, increases oxidative metabolism at rest and during endurance exercise. However, it is not known whether oxygen uptake during recovery from endurance exercise is increased when experiencing symptoms of EIMD. Therefore, the purpose of this study was to investigate the effects of EIMD on physiological and metabolic responses before, during and after sub-maximal running. After a 12 h fast, eight healthy male participants completed baseline measurements comprising resting metabolic rate (RMR), indirect markers of EIMD, 10 min of sub-maximal running and 30 min of recovery to ascertain excess post-exercise oxygen consumption (EPOC). Measurements were then repeated at 24 and 48 h after 100 Smith-machine squats. Data analysis revealed significant (P<0.05) increases in muscle soreness and creatine kinase (CK) and decreases in peak knee extensor torque at 24 and 48 h after squatting exercise. Moreover, RMR, physiological, metabolic and perceptual responses during sub-maximal running and EPOC were increased in the two days after squatting exercise (P<0.05). It is suggested that the elevated RMR was a consequence of a raised energy requirement for the degradation and resynthesis of damaged muscle fibres. The increased oxygen demand during sub-maximal running after muscle damage was responsible for the increase in EPOC. Individuals engaging in unaccustomed resistance exercise that results in muscle damage should be mindful of the increases in resting energy expenditure and increased metabolic demand to exercise in the days that follow.     

离心力竭运动对大鼠骨骼肌肌浆网Ca^2＋-ATP酶活性的影响

目的：采用大鼠下坡跑运动损伤模型,研究离心力竭运动后不同时刻大鼠骨骼肌肌浆网Ca^2＋-ATP酶活性的变化,探讨离心力竭运动所致骨骼肌超微结构损伤机制,为科学运动训练及运动恢复提供实验和理论依据。方法：雄性SD大鼠60只随机分为6组（每组10只）：安静对照组、运动后即刻组、12h组、24h组、48h组和72h组,以速度16m/min,坡度-16°进行跑台运动,运动100min,休息5min,再运动100min,在不同时刻观察大鼠肱三头肌肌浆网Ca^2＋-ATP酶活性的变化。结果：运动后即刻肌浆网Ca^2＋-ATP酶活性与对照组相比显著下降（P〈0.01）,随后开始恢复,运动后24h接近对照组水平（P〉0.05）,运动后48h已完全恢复到对照组水平。结论：离心力竭运动后即刻大鼠肱三头肌肌浆网Ca^2＋-ATP酶活性显著下降,随后逐渐恢复,运动后24h明显恢复,至48h已完全恢复,肌浆网Ca^2＋-ATP酶活性的变化可以间接评定运动后骨骼肌的损伤。     

Creatine kinase, myosin heavy chains and magnetic resonance imaging after eccentric exercise

The aim of this study was to examine the relationship between myosin heavy chain (MHC) release as a specific marker of slow-twitch muscle fibre breakdown and magnetic resonance imaging (MRI) of skeletal muscle injury after eccentric exercise. The effects of a single series of 70 high-intensity eccentric contractions of the quadriceps femoris muscle group (single leg) on plasma concentrations of creatine kinase and MHC fragments were assessed in 10 young male sport education trainees before and 1 and 4 days after exercise. To visualize muscle injury, MRI of the loaded thigh was performed before and 4 days after the eccentric exercise. All participants recorded an increase (P < 0.05) in creatine kinase after exercise. In five participants, T2 signal intensity was unchanged post-exercise compared with pre-exercise and MHC plasma concentration was normal; however, they showed an increase (P < 0.05) in creatine kinase after exercise. For the remaining five participants, there was an increase in T2 signal intensity of the loaded vastus intermedius and vastus lateralis. These changes in MRI were accompanied by an increase in MHC plasma concentration (P< 0.01) as well as an increase in creatine kinase (P < 0.01). We suggest that changes in MRI T, signal intensity after muscle damage induced by eccentric exercise are closely related to damage to structurally bound contractile filaments of some muscle fibres. Additionally, MHC plasma release indicates that this damage affects not only fast-twitch fibres but also some slow-twitch fibres.     

牛磺酸补充降低大鼠急性离心运动导致的骨骼肌微损伤程度

研究目的:研究补充牛磺酸对离心运动后骨骼肌超微结构损伤程度、血清丙二醛(MDA)含量和肌细胞浆Ca2+浓度的影响,探讨牛磺酸在减轻离心运动后骨骼肌损伤方面的作用.对象:成年雄性SD大鼠72只,方法:对照实验研究,随机将大鼠分为安静对照组和补水运动组、补牛磺酸运动组两个运动组,再按照动物取材时间将运动组分为运动后即刻组、24 h组、48 h组和72 h组,补牛磺酸组大鼠每日按400mg/kg灌胃一次牛磺酸溶液.两周后大鼠进行一次性下坡跑运动,速度为16 m/min,坡度为-16°,运动时间为120 min.主要观察指标:动物处死后电镜下观察比目鱼肌纤维Z线、测定血清丙二醛(MDA)和肌细胞浆内Ca2+浓度.结果:(1)补充牛磺酸运动组电镜下肌纤维损伤程度减轻,Z线异常,百分率显著低于补水运动组(P<0.05);(2)补充牛磺酸运动组血清MDA含量和肌细胞浆Ca2+浓度显著低于补水运动组 (P<0.05).结论:(1)高强度离心运动后EIMD的发生与自由基生成增多,胞浆钙超载有关;(2)补充牛磺酸能够抑制脂质过氧化反应,降低胞浆钙离了浓度,减轻骨骼肌损伤程度.     

Effect of combined carbohydrate-protein ingestion on markers of recovery after simulated rugby union match-play

In this study, we investigated the effect of ingesting carbohydrate alone or carbohydrate with protein on functional and metabolic markers of recovery from a rugby union-specific shuttle running protocol. On three occasions, at least one week apart in a counterbalanced order, nine experienced male rugby union forwards ingested placebo, carbohydrate (1.2 g · kg body mass(-1) · h(-1)) or carbohydrate with protein (0.4 g · kg body mass(-1) · h(-1)) before, during, and after a rugby union-specific protocol. Markers of muscle damage (creatine kinase: before, 258 ± 171 U · L(-1) vs. 24 h after, 574 ± 285 U · L(-1); myoglobin: pre, 50 ± 18 vs. immediately after, 210 ± 84 nmol · L(-1); P < 0.05) and muscle soreness (1, 2, and 3 [maximum soreness = 8] for before, immediately after, and 24 h after exercise, respectively) increased. Leg strength and repeated 6-s cycle sprint mean power were slightly reduced after exercise (93% and 95% of pre-exercise values, respectively; P < 0.05), but were almost fully recovered after 24 h (97% and 99% of pre-exercise values, respectively). There were no differences between trials for any measure. These results indicate that in experienced rugby players, the small degree of muscle damage and reduction in function induced by the exercise protocol were not attenuated by the ingestion of carbohydrate and protein.     

Creatine kinase,myosin heavy chains and magnetic resonance imaging after eccentric exercise

The aim of this study was to examine the relationship between myosin heavy chain (MHC) release as a specific marker of slow-twitch muscle fibre breakdown and magnetic resonance imaging (MRI) of skeletal muscle injury after eccentric exercise. The effects of a single series of 70 high-intensity eccentric contractions of the quadriceps femoris muscle group (single leg) on plasma concentrations of creatine kinase and MHC fragments were assessed in 10 young male sport education trainees before and 1 and 4 days after exercise. To visualize muscle injury, MRI of the loaded thigh was performed before and 4 days after the eccentric exercise. All participants recorded an increase ( P ? 0.05) in creatine kinase after exercise. In five participants, T2 signal intensity was unchanged post-exercise compared with pre-exercise and MHC plasma concentration was normal; however, they showed an increase ( P ? 0.05) in creatine kinase after exercise. For the remaining five participants, there was an increase in T2 signal intensity of the loaded vastus intermedius and vastus lateralis. These changes in MRI were accompanied by an increase in MHC plasma concentration ( P ? 0.01) as well as an increase in creatine kinase ( P ? 0.01). We suggest that changes in MRI T2 signal intensity after muscle damage induced by eccentric exercise are closely related to damage to structurally bound contractile filaments of some muscle fibres. Additionally, MHC plasma release indicates that this damage affects not only fast-twitch fibres but also some slow-twitch fibres.     

The time-frame of acute resistance exercise effects on football skill performance: The impact of exercise intensity

Abstract

The purpose of this study was to determine the recovery rate of football skill performance following resistance exercise of moderate or high intensity. Ten elite football players participated in three different trials: control, low-intensity resistance exercise (4 sets, 8–10 repetitions/set, 65–70% 1 repetition maximum [1RM]) and high-intensity resistance exercise (4 sets, 4–6 repetitions/set, 85–90% 1RM) in a counterbalanced manner. In each experimental condition, participants were evaluated pre, post, and at 24, 48, 72 h post exercise time points. Football skill performance was assessed through the Loughborough Soccer Passing Test, long passing, dribbling, shooting and heading. Delayed onset muscle soreness, knee joint range of motion, and muscle strength (1RM) in squat were considered as muscle damage markers. Blood samples analysed for creatine kinase activity, C-reactive protein, and leukocyte count. Passing and shooting performance declined (P < 0.05) post-exercise following resistance exercise. Strength declined post-exercise following high-intensity resistance exercise. Both trials induced only a mild muscle damage and inflammatory response in an intensity-dependent manner. These results indicate that football skill performance is minimally affected by acute resistance exercise independent of intensity suggesting that elite players may be able to participate in a football practice or match after only 24 h following a strength training session.     

Corticospinal changes induced by fatiguing eccentric versus concentric exercise

The present study assessed neuromuscular and corticospinal changes during and after a fatiguing submaximal exercise of the knee extensors in different modes of muscle contraction. Twelve subjects performed two knee extensors exercises in a concentric or eccentric mode, at the same torque and with a similar total impulse. Exercises consisted of 10 sets of 10 repetitions at an intensity of 80% of the maximal voluntary isometric contraction torque (MVIC). MVIC, maximal voluntary activation level (VAL) and responses of electrically evoked contractions of the knee extensors were assessed before and after exercise. Motor evoked potential amplitude (MEP) and cortical silent period (CSP) of the vastus medialis (VM) and rectus femoris (RF) muscles were assessed before, during and after exercise. Similar reductions of the MVIC (?13%), VAL (?12%) and a decrease in the peak twitch (?12%) were observed after both exercises. For both VM and RF muscles, MEP amplitude remained unchanged during either concentric or eccentric exercises. No change of the MEP amplitude input–output curves was observed post-exercise. For the RF muscle, CSP increased during the concentric exercise and remained lengthened after this exercise. For the VM muscle, CSP was reduced after the eccentric exercise only. For a similar amount of total impulse, concentric and eccentric knee extensor contractions led to similar exercise-induced neuromuscular response changes. For the two muscles investigated, no modulation of corticospinal excitability was observed during or after either concentric or eccentric exercises. However, intracortical inhibition showed significant modulations during and after exercise.     

离心运动伴不同程度的血流限制对外周疲劳及心脏自主神经功能的效应研究

目的:探讨急性离心运动伴4种不同程度的血流限制对年轻女性外周疲劳及心脏自主神经功能的影响,综合评价各方案的安全性,为长期血流限制运动干预提供参考。方法:将40名女大学生随机分为4组,分别进行小强度抗阻(30%1RM)伴0%(CON组)、40%(BFR₄₀组)、60%(BFR₆₀组)和80%(BFR80组)动脉闭塞压(AOP)的血流限制运动。各小组进行4组伸膝离心运动,第1组重复30次,后3组重复15次,组间休息30 s。检测运动前、运动后即刻、15 min、30 min、1 h以及24 h的骨骼肌收缩性能(最大径向位移、收缩速度)、最大等长力量和心脏自主神经功能。结果:1)与CON组相比,BFR₄₀组的副交感神经活性受到轻微抑制(P<0.05),可在运动后30 min内恢复(P>0.05);2)BFR₆₀组的最大等长力量在运动后显著下降(P<0.01),副交感神经活性进一步抑制(P<0.01),交感神经支配增强(P<0.05),运动后30 min内恢复交感—副交感神经的平衡性(P>0.05);3)BFR80组运动后诱发显著的外周疲劳(P<0.01),使副交感恢复显著延迟,交感活性大幅增强(P<0.05),需更长时间恢复交感—副交感神经的平衡性(24 h内);4)相关性分析显示,副交感神经活性分别与最大径向位移(r=0.65)、收缩速度(r=0.62)和最大等长力量(r=0.55)呈正相关(P<0.05),交感神经活性与上述3个指标呈负相关(P<0.05)。结论:血流限制运动中,40%AOP会抑制迷走神经活性;60%AOP可明显影响交感神经活性和交感—副交感调控的平衡性;80%AOP可诱发显著的外周疲劳,且与心脏自主神经调控密切相关。综上所述,不建议心血管风险高的患者使用80%AOP训练。     

Electromyographic analysis of exercise resulting in symptoms of muscle damage

Surface electromyographic (EMG) signals were recorded from the hamstring muscles during six sets of submaximal isokinetic (2.6 rad x s(-1)) eccentric (11 men, 9 women) or concentric (6 men, 4 women) contractions. The EMG per unit torque increased during eccentric (P < 0.01) but not during concentric exercise. Similarly, the median frequency increased during eccentric (P < 0.01) but not during concentric exercise. The EMG per unit torque was lower for submaximal eccentric than maximum isometric contractions (P < 0.001), and lower for submaximal concentric than maximum isometric contractions (P < 0.01). The EMG per unit torque was lower for eccentric than concentric contractions (P < 0.05). The median frequency was higher for submaximal eccentric than maximum isometric contractions (P < 0.001); it was similar, however, between submaximal concentric and maximum isometric contractions (P = 0.07). Eccentric exercise resulted in significant isometric strength loss (P < 0.01), pain (P < 0.01) and muscle tenderness (P < 0.05). The greatest strength loss was seen 1 day after eccentric exercise, while the most severe pain and muscle tenderness occurred 2 days after eccentric exercise. A lower EMG per unit torque is consistent with the selective recruitment of a small number of motor units during eccentric exercise. A higher median frequency during eccentric contractions may be explained by selective recruitment of fast-twitch motor units. The present results are consistent with the theory that muscle damage results from excessive stress on a small number of active fibres during eccentric contractions.     

急性低氧对优秀男子自行车运动员递增负荷运动时肌氧含量的影响

目的:探讨急性低氧环境下递增负荷运动时肌氧含量的变化。方法:通过无损伤近红外光谱学技术(NIRS)监测11名优秀男子自行车运动员常氧和急性低氧下进行递增负荷运动时肌氧含量和心肺系统功能的变化。结果:1)低氧运动时,无氧阈(VT)和最大摄氧量(VO2max)出现时对应的心率、指动脉血氧饱和度(SpO2)、气体代谢和功率均下降,显著低于常氧运动时的值;2)低氧环境下,从开始运动到75%最大功率,Δ[HbO2]降低、Δ[HHb]增高;由75%至100%最大功率时,Δ[HbO2]保持不变,而Δ[HHb]和Δ[THb]增加;在4个不同功率等级下低氧Δ[HbO2]均显著高于常氧值,Δ[HHb]在50%、75%和100%最大功率时均显著低于常氧对应值。结论:1)男子自行车运动员低氧下运动时低氧通气反应高于常氧水平,说明提高自行车运动员在高原训练时的低氧通气反应有利于提高其有氧能力,进而提高运动成绩。2)低氧运动时Δ[HbO2]高于常氧值,Δ[HHb]低于常氧值,提示肌氧含量是反映肌肉疲劳程度的敏感指标。     

Electromyographic analysis of exercise resulting in symptoms of muscle damage

Surface electromyographic (EMG) signals were recorded from the hamstring muscles during six sets of submaximal isokinetic (2.6 rad s -1 ) eccentric (11 men, 9 women) or concentric (6 men, 4 women) contractions. The EMG per unit torque increased during eccentric (P < 0.01) but not during concentric exercise. Similarly, the median frequency increased during eccentric (P < 0.01) but not during concentric exercise. The EMG per unit torque was lower for submaximal eccentric than maximum isometric contractions (P < 0.001), and lower for submaximal concentric than maximum isometric contractions (P < 0.01). The EMG per unit torque was lower for eccentric than concentric contractions (P < 0.05). The median frequency was higher for submaximal eccentric than maximum isometric contractions (P < 0.001); it was similar, however, between submaximal concentric and maximum isometric contractions (P = 0.07). Eccentric exercise resulted in significant isometric strength loss (P < 0.01), pain (P < 0.01) and muscle tenderness (P < 0.05). The greatest strength loss was seen 1 day after eccentric exercise, while the most severe pain and muscle tenderness occurred 2 days after eccentric exercise. A lower EMG per unit torque is consistent with the selective recruitment of a small number of motor units during eccentric exercise. A higher median frequency during eccentric contractions may be explained by selective recruitment of fast-twitch motor units. The present results are consistent with the theory that muscle damage results from excessive stress on a small number of active fibres during eccentric contractions.     

Effect of warm-up exercise on delayed-onset muscle soreness

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.     

Threshold frequency of an electrically induced cramp increases following a repeated,localized fatiguing exercise

Abstract

Though clinical observations and laboratory data provide some support for the neuromuscular imbalance theory of the genesis of exercise-associated muscle cramps, no direct evidence has been published. The purpose of this study was to determine the effect of local muscle fatigue on the threshold frequency of an electrically induced muscle cramp. To determine baseline threshold frequency, a cramp was electrically induced in the flexor hallucis brevis of 16 apparently healthy participants (7 males, 9 females; age 25.1 ± 4.8 years). The testing order of control and fatigue conditions was counterbalanced. In the control condition, participants rested in a supine position for 30 min followed by another cramp induction to determine post-threshold frequency. In the fatigue condition, participants performed five bouts of great toe curls at 60% one-repetition maximum to failure with 1 min rest between bouts followed immediately by a post-threshold frequency measurement. Repeated-measures analysis of variance and simple main effects testing showed post-fatigue threshold frequency (32.9 ± 11.7 Hz) was greater (P < 0.001) than pre-fatigue threshold frequency (20.0 ± 7.7 Hz). An increase in threshold frequency seems to demonstrate a decrease in one's propensity to cramp following the fatigue exercise regimen used. These results contradict the proposed theory that suggests cramp propensity should increase following fatigue. However, differences in laboratory versus clinical fatiguing exercise and contributions from other sources, as well as the notion of a graded response to fatiguing exercise, on exercise-associated muscle cramp and electrically induced muscle cramp should be considered.