Knee joint neuromuscular activation performance during muscle damage and superimposed fatigue (original) (raw)
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Prolonged intermittent high intensity exercise impairs neuromuscular performance of the knee flexors
European Journal of Applied Physiology, 1998
This study investigated the eect of prolonged intermittent high intensity exercise upon the isokinetic leg strength and electromechanical delay of the knee¯exors. Seven male collegiate soccer players were exposed to: (i) a prolonged intermittent high intensity exercise task (PI-HIET) which required subjects to complete a single-leg pedalling task, with the preferred limb, (75 rpm for all constant-load portions of the task) consisting of 48´1.8 minute cycles of exercise, and (ii) a control task consisting of no exercise. Pre-, mid-and post-PIHIET gravity corrected indices of knee¯exion angle-speci®c torque (0.44 rad knee¯exion (AST); 0 rad full knee extension; [1.05 rad á s A1 ]) were made for both intervention and control limbs. Electromechanical delay (EMD) of the m. biceps femoris during supine knee¯exion movements was evaluated in the preferred leg on both intervention and control days. Repeated measures ANOVAs revealed signi®cant condition (intervention; control) by time (pre; mid; post) interactions for both knee¯exor AST (F [2,12] 4.8; p`0X03) and EMD (F [2,12] 4.1; p`0X05). AST was observed to decrease by 16% and EMD increase by 30% pre to post intervention. These observations suggest an impairment of neuromuscular control and the ability to maintain force generation in the knee¯exors, near the extremes of the range of motion during prolonged intermittent high-intensity exercise activities. Changes of this magnitude may pose a threat to the integrity of the knee joint.
Frontiers in Physiology
Purpose: To examine the effects of fatiguing isometric contractions on maximal eccentric strength and electromechanical delay (EMD) of the knee flexors in healthy young adults of different training status. Methods: Seventy-five male participants (27.7 ± 5.0 years) were enrolled in this study and allocated to three experimental groups according to their training status: athletes (ATH, n = 25), physically active adults (ACT, n = 25), and sedentary participants (SED, n = 25). The fatigue protocol comprised intermittent isometric knee flexions (6-s contraction, 4-s rest) at 60% of the maximum voluntary contraction until failure. Pre-and post-fatigue, maximal eccentric knee flexor strength and EMDs of the biceps femoris, semimembranosus, and semitendinosus muscles were assessed during maximal eccentric knee flexor actions at 60, 180, and 300°/s angular velocity. An analysis of covariance was computed with baseline (unfatigued) data included as a covariate. Results: Significant and large-sized main effects of group (p ≤ 0.017, 0.87 ≤ d ≤ 3.69) and/or angular velocity (p < 0.001, d = 1.81) were observed. Post hoc tests indicated that regardless of angular velocity, maximal eccentric knee flexor strength was lower and EMD was longer in SED compared with ATH and ACT (p ≤ 0.025, 0.76 ≤ d ≤ 1.82) and in ACT compared with ATH (p = ≤0.025, 0.76 ≤ d ≤ 1.82). Additionally, EMD at post-test was significantly longer at 300°/s compared with 60 and 180°/s (p < 0.001, 2.95 ≤ d ≤ 4.64) and at 180°/s compared with 60°/s (p < 0.001, d = 2.56), irrespective of training status. Conclusion: The main outcomes revealed significantly higher maximal eccentric strength and shorter eccentric EMDs of knee flexors in individuals with higher training status (i.e., athletes) following fatiguing exercises. Therefore, higher training status is associated with better neuromuscular functioning (i.e., strength, EMD) of the hamstring muscles in fatigued condition. Future longitudinal studies are needed to substantiate the clinical relevance of these findings.
Isokinetics and Exercise Science
Effect of isotonic and isometric knee extension exercises on mechanical and electromyographical specificity of fatigue. Isokinetics and Exercise Science , 10:167-175 ***Note: Figures may be missing from this format of the document Abstract.: This study investigated the effects of isotonic and isometric knee extension exercises on strength, power, and surface EMG in male and female populations. Using the knee extensors, ten males and ten females performed a 120 s MVIC and 120 maximal isotonic contractions. Prior to each exercise (t = pre) knee extensor isometric peak torque (strength) and average peak power (power) were tested utilizing three, 3 s MVIC's and three maximal isotonic contractions, respectively. Following each exercise, strength and power were assessed immediately after (t =: 00) and at 2.5 (t =: 02.5), 5 (t =: 05), 10 (t =: 10), and 15 (t =: 15) minutes. All strength and power measures were normalized to the respective t = pre value. Vastus lateralis surface EMG signals were collected during all muscle testing and normalized to the respective tire value. Following isometric exercise, both strength and power at t =: 00 (68.7% ± 8.7% & 88.0% ± 8.7%) and t =: 02.5 (82.2% ± 17.8% & 95.2% ± 5.0%) significantly decreased from t=pre (100% ± 0.0%) (p < 0.05) with greater decreases in strength at each time point (p < 0.05). EMG analysis revealed a significant EMG amplitude decrease (p < 0.05) at t =: 00 and t =: 02.5 during strength testing with respect to t=pre. Following isotonic exercise, both strength and power at t =: 00 (68.0% ± 13.2% & 38.8% ± 10.7%) and t =: 02.5 (84.5% ± 14.9% & 81.6% ± 14.5%) significantly decreased from t=pre (100% ± 0.0%) with a greater power decrease at t =: 00 (p < 0.05). The EMG amplitude of males was significantly less at t =: 00 than the respective EMG amplitude for females (p < 0.05) (irrespective of testing condition). We conclude that muscle performance in the fatigued state is dependent upon the type of exercise performed. Article: INTRODUCTION: During the past years of research addressing muscle performance during and following fatiguing exercise, the isometric contraction has been considered the gold standard of muscle force producing capability in the laboratory setting. The muscle force production values acquired from isometric contractions are often referred to as "strength" [11]. However in sporting activities the majority of muscle contractions are dynamic in nature. Power, a variable that takes into account contraction force and velocity, is important in sports that demand explosive movements. Throughout the remainder of this paper strength will refer to isometric torque production and power will refer to dynamic, maximal efforts of the muscle/joint complex.
Nonlocal muscle fatigue occurs when fatiguing 1 muscle alters performance of another rested muscle. The purpose of the study was to investigate if fatiguing 2 separate muscles would affect the same rested muscle, and if fatiguing the same muscle would affect 2 separate muscles. Twenty-one trained males participated in 2 studies (n = 11; n = 10). Subjects performed 2 pre-test maximum voluntary contractions (MVCs) with the nondominant knee extensors. Thereafter they performed two 100-s MVCs with their dominant knee extensors, elbow flexors, or rested. Between and after the sets, a single MVC with the nondominant rested knee extensors was performed. Subsequently, 12 nondominant knee extensors repeated MVCs were completed. Force, quadriceps voluntary activation (VA), and electromyography (EMG) were measured. The same protocol was employed in study 2 except the nondominant elbow-flexors were tested. Study 1: Compared with control conditions, a significant decrease in nondominant knee extensors force, EMG, and VA was found under both fatiguing conditions (P ≤ 0.05; effect size (ES) = 0.91–1.15; 2%–8%). Additionally, decrements in all variables were found from the first post-intervention MVC to the last (P ≤ 0.05; ES = 0.82–2.4; 9%–20%). Study 2: No differences were found between conditions for all variables (P ≥ 0.33; ES ≤ 0.2; ≤3%). However, all variables decreased from the first post-intervention MVC to the last (P ≤ 0.05; ES = 0.4–3; 7.2%–19.7%). Whereas the rested knee extensors demonstrated nonlocal effects regardless of the muscle being fatigued, the elbow-flexors remained unaffected. This suggests that nonlocal effects are muscle specific, which may hold functional implications for training and performance. Résumé : La fatigue musculaire non localisée se présente lorsqu'un muscle fatigué modifie la performance d'un autre muscle reposé. Cette étude se propose d'examiner l'effet de l'épuisement de deux muscles distincts sur un même muscle reposé et l'effet de l'épuisement du même muscle se répercute sur deux muscles distincts. Vingt-et-un hommes entraînés participent a ` deux études (n = 11; n = 10). Les sujets effectuent avant le test deux contractions maximales volontaires (« MVC ») des extenseurs du genou du côté non dominant. Ensuite, ils effectuent deux MVC d'une durée de 100 s des extenseurs du genou, des fléchisseurs du coude du côté dominant ou ils se reposent. Entre les deux séries et après, les sujets effectuent une seule MVC des extenseurs du genou non épuisés du côté non dominant. Par la suite, les sujets effectuent 12 MVC des extenseurs du genou du côté non dominant. On évalue la force, le degré d'activation volontaire (« VA ») et l'activité myoélectrique (EMG) du quadriceps. On applique le même protocole dans la deuxième étude pour l'évaluation des fléchisseurs du coude du côté non dominant. Étude 1 : Comparativement a ` la condition de contrôle, on observe dans les deux conditions épuisantes une diminution significative de la force, de l'EMG et de la VA des extenseurs du genou du côté non dominant (P ≤ 0,05; ampleur de l'effet (AE) = 0,91–1,15; 2 %–8 %). De plus, on observe une diminution de toutes les variables a ` partir de la première jusqu'a ` la dernière MVC suivant l'intervention (P ≤ 0,05; AE = 0,82–2,4; 9 %–20 %). Étude 2 : On n'observe aucune différence des valeurs des variables d'une condition a ` l'autre (P ≥ 0,33; AE ≤ 0,2; ≤3 %). Toutefois, toutes les variables présentent une diminution a ` partir de la première jusqu'a ` la dernière MVC suivant l'intervention (P ≤ 0,05; AE = 0,4–3; 7,2 %–19,7 %). Les extenseurs reposés du genou ne présentent pas un effet localisé indépendamment du muscle épuisé et les fléchisseurs du coude ne sont pas touchés. Dès lors, les effets non localisés pourraient être spécifiques au muscle, ce qui suggère des implications fonction-nelles en matière d'entraînement et de performance. [Traduit par la Rédaction]
Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology, 2014
The aim of the study was to examine whether six weeks of endurance training minimizes the effects of fatigue on postural control during dynamic postural perturbations. Eighteen healthy volunteers were assigned to either a 6-week progressive endurance training program on a cycle ergometer or a control group. At week 0 and 7, dynamic exercise was performed on an ergometer until exhaustion and immediately after, the anterior-posterior centre of pressure (COP) sway was analyzed during full body perturbations. Maximal voluntary contractions (MVC) of the knee flexors and extensors, muscle fiber conduction velocity (MFCV) of the vastus lateralis and medialis during sustained isometric knee extension contractions, and power output were measured. Following the training protocol, maximum knee extensor and flexor force and power output increased significantly for the training group with no changes observed for the control group. Moreover, the reduction of MFCV due to fatigue changed for the tr...
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Effect of antagonist muscle fatigue on knee extension torque
Pflugers Archiv-european Journal of Physiology, 2003
The effect of hamstring fatigue on knee extension torque was examined at different knee angles for seven male subjects. Before and after a dynamic flexion fatigue protocol (180° s−1, until dynamic torque had declined by 50%), maximal voluntary contraction extension torque was measured at four knee flexion angles (90°, 70°, 50° and 30°). Maximal torque generating capacity and voluntary activation of the quadriceps muscle were determined using electrical stimulation. Average rectified EMG of the biceps femoris was determined. Mean dynamic flexion torque declined by 48±11%. Extensor maximal voluntary contraction torque, maximal torque generating capacity, voluntary activation and average rectified EMG at the four knee angles were unaffected by the hamstring fatigue protocol. Only at 50° knee angle was voluntary activation significantly lower (15.7%) after fatigue (P<0.05). In addition, average rectified EMG before fatigue was not significantly influenced by knee angle. It was concluded that a fatigued hamstring muscle did not increase the maximal voluntary contraction extension torque and knee angle did not change coactivation. Three possible mechanisms may explain the results: a potential difference in recruited fibre populations in antagonist activity compared with the fibres which were fatigued in the protocol, a smaller loss in isometric torque generating capacity of the hamstring muscle than was expected from the dynamic measurements and/or a reduction in voluntary activation.
Muscle coactivation is the activation of two or more muscles simultaneously around a joint. Coactivation of knee muscles especially quadriceps is considered to be an important phenomenon for the stabilization of patellofemoral joint. The purpose of this study was to investigate the Coactivation ratio of selected knee extensor muscles as measure of neuromuscular fatigue in relation to gender, performance and side (right and left) of male (n1=19) and female (n2=8) during isometric contraction. The isometric contraction consisted of performing knee extension with an angle between 0º to 10º with a load of 30 repetition maximum (RM) on the CYBEX exerciser. The statistical analysis applied were ANOVA with post hoc analysis to determine the influence of fatigue in terms of gender, performance and side (right and left). The results showed significant decrease in the coactivation ratio of the selected muscles pair during isometric contraction with progression of fatigue (time). It also showed male dominance behavior over females in coactivation of Vastus Medialis (VM) and Vastus Lateralis (VL) muscles.. The results of this study would help to better understand the changes in activation strategies that can provide valuable information regarding the mechanisms that alter neuromuscular activity.