Effects of hamstring‐emphasized neuromuscular training on strength and sprinting mechanics in football players

The objective of this study was to examine the effects of a neuromuscular training program combining eccentric hamstring muscle strength, plyometrics, and free/resisted sprinting exercises on knee extensor/flexor muscle strength, sprinting performance, and horizontal mechanical properties of sprint running in football (soccer) players. Sixty footballers were randomly assigned to an experimental group (EG) or a control group (CG). Twenty‐seven players completed the EG and 24 players the CG. Both groups performed regular football training while the EG performed also a neuromuscular training during a 7‐week period. The EG showed a small increases in concentric quadriceps strength (ES = 0.38/0.58), a moderate to large increase in concentric (ES = 0.70/0.74) and eccentric (ES = 0.66/0.87) hamstring strength, and a small improvement in 5‐m sprint performance (ES = 0.32). By contrast, the CG presented lower magnitude changes in quadriceps (ES = 0.04/0.29) and hamstring (ES = 0.27/0.34) concentric muscle strength and no changes in hamstring eccentric muscle strength (ES = ?0.02/0.11). Thus, in contrast to the CG (ES = ?0.27/0.14), the EG showed an almost certain increase in the hamstring/quadriceps strength functional ratio (ES = 0.32/0.75). Moreover, the CG showed small magnitude impairments in sprinting performance (ES = ?0.35/?0.11). Horizontal mechanical properties of sprint running remained typically unchanged in both groups. These results indicate that a neuromuscular training program can induce positive hamstring strength and maintain sprinting performance, which might help in preventing hamstring strains in football players.     

Acute effects of exercise on MR imaging of skeletal muscle: concentric vs eccentric actions

Eccentric (lengthening) muscle actions involve the forced lengthening of active muscles. Compared with concentric (shortening) muscle actions subjected to the same relative work load, eccentric actions have lower oxygen consumption requirements, fewer activated motor units, and less lactate production. This study was conducted to determine if T2-weighted MR could show any difference in muscles performing these specific types of actions and, therefore, be useful for physiologic investigations of eccentric and concentric actions. Five subjects performed exhaustive exercise by doing isolated concentric actions (raising a dumbbell, flexing at the elbow) and eccentric muscle actions (lowering a dumbbell, extending the contralateral arm). T2-weighted MR images of the arms were obtained immediately before and after exercise. Muscles that performed concentric actions had increases in signal intensity, whereas muscles that performed eccentric actions showed little or no change. T2 relaxation times increased significantly (p less than .01) in all volunteers, but T2 relaxation times for the muscles that performed concentric actions were significantly higher than those for muscles that performed eccentric actions (p less than .01). Therefore, T2 times increased with both concentric and eccentric actions, but the images failed to show the changes in the muscles that performed the eccentric actions. These data demonstrate that assessment of T2 values can be used to distinguish between muscles that perform concentric actions and those that perform eccentric actions, and this phenomenon may be useful for further physiologic investigations of these specific types of muscle actions.     

Effects of eccentric phase velocity of plyometric training on the vertical jump

The aim of this study was to compare the effects of plyometric training performed with rapid or slow stretch contraction on jump performance and muscle properties. Thirty males between the ages of 19 and 22 volunteered for the 8-week experiment. Subjects were divided into the following three groups: training group 1 (TG1), training group 2 (TG2), and control group (CG). Each of the two experimental groups underwent a unique training regimen. For the first group (TG1, n = 12): from a standing position the subject flexed his knees to a 90 degrees angle with velocity standardized and controlled at 0.4 m/s and immediately performed a leg extension as quickly as possible. For the second group (TG2, n = 12): from a standing position, the subject flexed his knees to a 90 degrees angle with velocity standardized at 0.2 m/s and then performed a leg extension as quickly as possible. Each exercise consisted of six sets of ten repetitions with a barbell on the shoulders at 70 % of the maximal isometric force (1 RM). The 70 % load was modified at two-week intervals by evaluating a new 1 RM. Exercises were performed four times a week over the eight-week period. The third group (CG, n = 6), served as the control group. Maximal isometric force (MVC), maximal concentric force, squat jump (SJ) and counter movement jump (CMJ) exercises were performed before and after the training program. Subjects were filmed (100 Hz) and each jump was divided into three phases: eccentric phase (ECC), transition phase (TR) and concentric phase (CON). Surface EMG was used to determine the changes in the electromyographic (EMG) activity before and after the training program. There was an increase in leg extension force, velocity and electrical activity for SJ and CMJ for the two training groups (p < 0.05). However, TG1 showed a significant advantage in CMJ performance as well as a significant decrease in TR compared to the TG2 (p < 0.05). The results of this study show that when plyometric training is performed with rapid stretch contraction the CMJ jump height increases and the TR decreases.     

Strength gains following different combined concentric and eccentric exercise regimens

BACKGROUND: Loss of muscle strength and cross-sectional area is a well-recognized consequence of spaceflight. Existing countermeasures have not been fully effective in preventing muscle weakness and atrophy in microgravity. Resistance exercise programs that consist of both eccentric and concentric actions have resulted in strength and muscle mass gains in ground-based studies. HYPOTHESES: 1) A concentric/eccentric combination exercise regimen (with a bias of either concentric or eccentric exercise) will result in a greater strength gain than concentric exercise alone; and 2) an eccentrically biased regimen will result in the greatest strength gain of all. METHODS: The 31 subjects were randomly assigned to one of three isokinetic exercise groups (CON-ECC: 75% concentric and 25% eccentric; ECC-CON: 75% eccentric and 25% concentric; CON: 100% concentric); each subject trained the right leg 3 d per week for 5 wk. Pre- and post-training isokinetic concentric/ eccentric strength tests and DEXA scans assessed changes in muscle strength and/or mass. RESULTS: All three groups showed an increase in eccentric muscle strength with the CON group showing the smallest gain (10.1%). Significantly larger gains were noted in the two combination groups (19.5%, 18.1%; p < 0.042), with the largest gains in eccentric strength. No significant change was noted in muscle mass. CONCLUSIONS: A resistance exercise protocol which includes eccentric as well as concentric exercise, particularly when the eccentric exercise is emphasized, appears to result in greater strength gains than concentric exercise alone. Findings suggest eccentric exercise may be an important component of the in-flight resistance exercise protocol for long-duration spaceflight.     

Effects of eccentric versus concentric training on thigh muscle strength and EMG

The purpose of this study was to compare pure eccentric and concentric strength training regarding possible specific effects of muscle action type on neuromuscular parameters, such as a decreased inhibition during maximal voluntary eccentric actions. Two groups of young healthy adult men performed 10 weeks of either eccentric or concentric unilateral isokinetic knee extensor training at 90 degrees.s(-1), 4 sets of 10 maximal efforts, 3 days a week. Knee extensor torque and surface EMG from the quadriceps and hamstring muscle groups were collected and quantified in a window between 30 and 70 degrees knee angle (range of motion 90-5 degrees ) during maximal voluntary eccentric and concentric knee extensor actions at 30, 90, and 270 degrees.s(-1). Changes in strength of the trained legs revealed more signs of specificity related to velocity and contraction type after eccentric than concentric training. No major training effects were present in eccentric to concentric ratios of agonist EMG or in relative antagonist (hamstring) activation. Thus, for the trained leg, the muscle action type and speed specific changes in maximal voluntary eccentric strength could not be related to any effects on neural mechanisms, such as a selective increase in muscle activation during eccentric actions. Interestingly, with both types of training there were specific cross-education effects, that is, action type and velocity specific increases in strength occurred in the contralateral, untrained, leg, accompanied by a specific increase in eccentric to concentric EMG ratio after eccentric training.     

Importance of eccentric actions in performance adaptations to resistance training.

The inability of the exercises presently used during space-flight to maintain muscle strength and mass may reflect the absence of eccentric (ecc) muscle actions. This study examined the importance of ecc actions in performance adaptations to resistance training. Middle-aged males performed 4-5 sets of 6-12 repetitions (rep) per set of the leg press and leg extension exercises 2 d each week for 19 weeks. Group CON/ECC (n = 9) performed each rep with concentric (con) and ecc actions, group CON (n = 8) with only con actions. Group CON/CON (n = 10) performed twice as many sets with only con actions. The resistance per set was selected to induce failure within the prescribed number of rep. Eight subjects did not train and served as controls. The increase in the three rep maximum (3RM) after training, in general, showed a hierarchy such that CON/ECC greater than CON/CON greater than CON. The differences (p less than 0.05) were: leg press 3RM with con and ecc actions, CON/ECC greater than CON/CON greater than CON (26 greater than 15 greater than 8%); leg press 3RM with only con actions, CON/ECC or CON/CON greater than CON (22 or 18 greater than 14%); and leg extension 3RM with con and ecc actions, CON/ECC greater than CON (29 greater than 16%). These differences (p less than 0.05) were still evident after 1 month of de-training. The results indicate that omission of ecc actions from resistance training compromises increases in strength, probably because intensity is not optimal.(ABSTRACT TRUNCATED AT 250 WORDS)     

Eccentric reinforcement of the ankle evertor muscles after lateral ankle sprain

To compare two methods of ankle evertor muscle reinforcement after ankle sprain: concentric vs eccentric reinforcement. Eighteen subjects practising sport with first episode of ankle sprain. The first randomized group underwent conventional physical therapy including concentric reinforcement of the evertor ankle muscles [concentric group (CG)]. The second randomized group underwent eccentric reinforcement [eccentric group (EG)]. At the end of the physical therapy, the strength of the evertor muscles was tested using an isokinetic dynamometer. The measurements were peak torques in the concentric and eccentric modes; ankle strength deficits, expressed as percentages of the healthy ankle values recorded in the concentric and eccentric modes; ratios between concentric/eccentric values. After the concentric reinforcement, in the CG group, there is both significant concentric strength deficit and an eccentric strength deficit on the injured side in comparison with the healthy side. After the eccentric reinforcement in the EG group, the muscle strength was significantly greater during concentric movements. Eccentric rehabilitation therefore restored the strength of the injured evertor muscles. These results show the value of this method, especially as the weakness of these muscles after sprains is one of the main risk factors contributing to instability and the recurrence of sprains.     

Effects of power training on neuromuscular performance and mechanical efficiency

Effects of power training with stretch-shortening cycle (SSC) exercises on mechanical efficiency (ME) were investigated with 9 young women who trained 3 times a week for 4 months. The training included various types of jumping exercises. Before and after the training as well as after the detraining (2 months) the subjects performed 6 different submaximal exercises with a special sledge apparatus. Each exercise involved 60 muscle actions lasting for a total of 3 min per testing condition. The work intensities were determined individually according to the recordings of distance obtained during the single maximal concentric exercises. The training caused the greatest changes of ME in conditions of higher prestretch intensities. The ME values changed from 49.3 ± 12.9% to 55.4 ± 12.1% in pure eccentric exercises and from 39.5 ± 4.6% to 46.1 ± 5.0% in SSC exercises during the training. After the training, the subjects preactivated their leg extensor muscles earlier before the impact, and the eccentric working phase was more powerful, because of higher tendomuscular stiffness. Higher preactivation of the measured muscles, higher flexion of knee and increased dorsiflexion of ankle joints in the beginning of contact caused the increased stiffness, possibly through more powerful reflex activation. At the same time the metabolic demands of muscles decreased, causing the increases of ME.     

不同运动方式对大鼠骨骼肌急性拉伤修复过程中MHC-Ⅱ,COL-Ⅰ、COL-Ⅲ的影响

目的:了解不同运动方式(离心运动、向心运动)对骨骼肌拉伤愈合过程中肌肉再生和纤维化过程的影响。方法:将120只成年雌性SD大鼠随机分为空白组(BC组,n=8)、即刻组(IM组,n=8)、第1周组(1W组,n=8)、自然愈合组(NC组,n=32)、向心运动组(CE组,n=32)、离心运动组(EE组,n=32)。造成腓肠肌急性拉伤模型1周后,对CE组、EE组分别进行为期4周的向心和离心训练。IM组造模即刻、1W组造模后7天、BC组造模后18天取材;其余各组分别在造模后第14天、第21天、第28天、第35天4个时间段,每个时间段随机选择8只大鼠取材,用免疫组化的方法检测大鼠腓肠肌Ⅱ型肌球蛋白重链(MHC-Ⅱ)及Ⅰ、Ⅲ型胶原(COL-Ⅰ和COL-Ⅲ)水平。结果:损伤恢复的各个阶段,CE组MHC-Ⅱ水平较NH组和EE组高,并且恢复速度较快,而COL-Ⅰ和COL-Ⅲ水平较NH组和EE组低;EE组MHC-Ⅱ水平较NH组和CE组低,COL-Ⅰ水平较NH组低但高于CE组;COL-Ⅲ水平高于CE组和NH组。结论:不同运动方式对骨骼肌急性损伤后的修复过程影响不同,向心运动能有效促进损伤骨骼肌MHC-Ⅱ合成,从而加快骨骼肌再生,离心运动对MHC-Ⅱ合成的影响不明显。运动通过减少COL-Ⅰ表达和合成来抑制骨骼肌的纤维化,向心运动作用比离心运动更加明显。在损伤修复早期,COL-Ⅲ水平提高,使骨骼肌具备一定的强度和力学稳定性,有利于损伤后功能的快速代偿,而后期COL-Ⅲ水平持续增高可能促进和延长骨骼肌的纤维化过程。     

Central versus peripheral adaptations following eccentric resistance training

Aim of the present investigation was to study the effects of an eccentric training on the neuromuscular properties of the plantar-flexor muscles. The experiment was carried out on 14 males divided into two groups (eccentric and control). Eccentric training consisted of six sets of six eccentric contractions at 120 % of one maximal concentric repetition and it was performed four times a week during four weeks. Before and after the 4-wk period, the plantar-flexor torque and the associated electromyographic activity were recorded during voluntary contractions (isometric, concentric and eccentric) and electrically induced contractions (twitch and tetanus), in order to distinguish central from peripheral adaptations. For the eccentric group, voluntary torque significantly increased after training independent of the action mode (relative gains 14 - 30 %, p < 0.05). This was associated with an increase in agonist EMG activity during isometric action and a decrease in antagonist coactivation in concentric (-27 %) and eccentric actions (-22 %) (p < 0.05). Voluntary activation level significantly increased from 80 +/- 5 % to 91 +/- 2 % (p < 0.05). Some of the twitch contractile properties (peak torque and maximal rate of twitch tension relaxation) were significantly modified (p < 0.05), but no changes were observed for the tetanus characteristics. These results allowed to conclude that the torque gains observed after the present training were more likely associated to central adaptations, affecting both agonist and antagonist muscles.     

Acute adaptation to low volume eccentric exercise.

PURPOSE: Many symptoms of eccentric muscle damage can be substantially reduced if a similar eccentric bout is repeated within several weeks of the initial bout. The purpose of this study was to determine whether a nondamaging, low repetition, low volume eccentric exercise bout could also provide a protective/adaptive effect. METHODS: Subjects were assigned to a control (CON), eccentric exercise (ECC), or low volume familiarized eccentric exercise group (LV+ECC). Before the study, the LV+ECC group performed six maximal eccentric contractions during two familiarization sessions. The main eccentric bout targeted the elbow flexor muscle group and consisted of 36 maximal eccentric contractions. Muscle soreness, upper arm girth, elbow angle, creatine kinase activity, isometric torque, and concentric and eccentric torque at 0.52 and 3.14 rad.s-1 were assessed 0, 1, 2, 3, 4, 7, and 10 d postexercise. RESULTS: No evidence of muscle damage was observed as a result of the low volume eccentric bouts. Nevertheless, with the exception of muscle soreness and concentric torque, all variables recovered more rapidly in the LV+ECC group (P < 0.05). CONCLUSION: Adaptation to eccentric exercise can occur in the absence of significant muscle damage. Exposure to a small number of nondamaging eccentric contractions can significantly improve recovery after a subsequent damaging eccentric bout. Furthermore, this adaptation appears to be mode-specific and not applicable to concentric contractions.     

Differential effects of exhaustive cycle ergometry on concentric and eccentric torque production

The purpose of this study was to investigate the potential differences in peak isokinetic concentric end eccentric torque following low- and high-intensity cycle exercise fatigue protocols. Ten healthy, recreationally-active men were tested in a balanced, randomized testing sequence for peak eccentric and concentric isokinetic torque (60 degrees/sec) immediately before and after three experimental conditions each separated by 48 hours: 1) a bout of high intensity cycling consisting of a maximal 90-second sprint; 2) a bout of low-intensity cycling at 60 rpm equated for total work with the high-intensity protocol: and 3) no exercise (control bout). Blood was drawn from an antecubital vein and plasma lactate concentrations were determined immediately before and after each experimental bout. Post-exercise plasma lactate concentrations were 15.1 +/- 2.5 and 4.7 +/- 1.9 mmol l(-1), respectively, following the high- and low-intensity protocols. The high intensity exercise bout resulted in the only post-exercise decrease in concentric and eccentric isokinetic peak torque. The percent decline in maximal force production was significantly (P< 0.05) greater for concentric muscle actions compared to eccentric (29 vs 15%, respectively). In conclusion, a 90-second maximal cycling sprint results in a significant decline in maximal torque of both concentric and eccentric muscle actions with the greatest magnitude observed during concentric muscle actions.     

Changes in urinary titin N-terminal fragments as a biomarker of exercise-induced muscle damage in the repeated bout effect

ObjectivesMuscle damage symptoms induced by unaccustomed eccentric contraction exercise can be reduced by repeating the experience several times. This phenomenon is termed the repeated bout effect. Although traditional biochemical markers require invasive blood sampling, biochemical measurements have recently been developed that can be non-invasively performed using urinary titin N-terminal fragment (UTF). However, it is unclear whether UTF can reflect the repeated bout effect. Therefore, the aim of the present study was to clarify whether UTF decreased with the repeated bout effect.DesignThis study compared changes in muscle damage markers between bouts of exercise performed for the first and second time.MethodsEight young men performed 30 eccentric exercises of the elbow flexor on the first day of the first week (Bout 1). A second bout of eccentric exercises, same as the first, was performed 2 weeks later, (Bout 2). The dependent variables were muscle soreness (SOR), maximal voluntary isometric contraction (MVIC), range of motion (ROM), creatine kinase (CK), and UTF. All dependent variables were analyzed using two-way analysis of variance.ResultsNo significant difference was observed in workload or peak torque between the first and second exercise bouts. SOR as well as CK and UTF were significantly lower and ROM and MVIC were significantly higher in Bout 2 in comparison to Bout 1.ConclusionsThese results suggest that UTF sensitively reflects the repeated bout effect and exercise-induced muscle damage can be non-invasively measured.     

Effects of number of eccentric muscle actions on first and second bouts of eccentric exercise of the elbow flexors

This study compared changes in indirect markers of muscle damage following eccentric exercise of the elbow flexors among the exercises consisting of different number of eccentric actions. Sixty male athletes were placed into one of the six groups (n=10 per group) based on the number of eccentric actions for the first (ECC1) and second exercise bouts (ECC2). Single bout groups (30, 50, and 70) performed ECC1 only, and repeated bout groups (30-30, 50-50, and 70-70) performed ECC2 3 days after ECC1. Another 10 male athletes performed different number of eccentric actions for ECC1 (30) and ECC2 (70) separated by 3 days (30-70). Changes in maximal isometric strength (MVC), range of motion (ROM), upper arm circumference (CIR), serum creatine kinase activity, myoglobin, and nitric oxide concentrations and muscle soreness for 10 days following ECC1 were compared among groups by two-way repeated measures ANOVA. Changes in MVC, ROM, and CIR following ECC1 were significantly (P<0.05) smaller for the groups that performed 30 eccentric actions compared with other groups. No significant differences between 30 and 30-30, 50 and 50-50, and 70 and 70-70 were evident for the changes in the measures for 10 days following ECC1 except for the acute decreases in MVC and ROM immediately after ECC2 for the repeated bout groups. The 30-30 and 30-70 groups showed similar changes in all criterion measures. It is concluded that recovery from eccentric exercise is not retarded by the second bout of eccentric exercise regardless of the number of eccentric actions.     

Effect of activation force on knee extensor torques

The purpose of this study was to determine whether the magnitude of the activation force, defined as the force that must be applied to the load cell in order to activate the resistance arm of an isokinetic dynamometer, affected knee extensor torques. Twenty-four healthy female subjects performed resisted knee extension through the range of 95 degrees to 5 degrees knee flexion, with a 5-s rest between concentric and eccentric muscle actions. Six exercise sets, composed of the combinations of activation force (20,50, and 100 N) and angular velocity (45 and 135 degrees.s-1), were randomly assigned on each of two occasions, completed within a 10-d period. Although peak torques were not affected by the activation force, average torques, eccentric torques at mid-range (50 degrees knee flexion), and torques during the initial portion of each muscle action (80 degrees knee flexion during concentric muscle actions and 20 degrees flexion during eccentric actions) increased as the activation force increased. The effect of the activation force tended to be more pronounced during eccentric than during concentric muscle actions, and at the faster angular velocity. Comparisons of torques should be based on similar test protocols, including activation force.     

Effects of short-term concentric vs. eccentric resistance training on single muscle fiber MHC distribution in humans

The purpose of this investigation was to determine the effects of a concentric vs. eccentric resistance training program on single muscle fiber myosin heavy chain (MHC) adaptations in humans. Fifteen sedentary, healthy males were divided into three groups: concentric training (CTG) (n = 6, 24.2 +/- 1.7 y, 181 +/- 2 cm, 82.5 +/- 4.6 kg), eccentric training (ETG) (n = 6, 23.7 +/- 1.6 y, 178 +/- 3 cm, 90.4 +/- 6.1 kg), and control (CTL) (n = 3, 23 +/- 1.5 y, 181 +/- 2 cm, 97 +/- 13.2 kg). The subjects performed 4 sets of 8 unilateral repetitions starting at 80 % of concentric 1-RM, 3 days/week for a total of 4 weeks. Subjects were tested pre- and post-training for concentric 1-RM. Muscle biopsies were obtained from the vastus lateralis pre- and post-training for determination of single fiber MHC isoform distribution using SDS-PAGE/silver staining (100 fibers analyzed/subject pre- and post-training). Fibers expressing more than one MHC isoform (i.e., hybrid fibers) were analyzed for relative MHC isoform proportions via densitometry. The training program resulted in a 19 % 1-RM strength gain for CTG (p < 0.05) with no change in ETG or CTL. MHC-IIx fibers decreased by 7 % in CTG (p < 0.05) and ETG had an 11 % increase in total hybrids (MHC-I/IIa + MHC-IIa/IIx) (p < 0.05). No other differences were noted in MHC distribution among the three groups. Densitometry analysis of hybrid fibers showed no change in relative MHC isoform proportions pre- to post-training for any group. These data suggest that the MHC distribution did not change dramatically as a result of 4 weeks of concentric vs. eccentric resistance training despite the increase in whole muscle strength from concentric muscle actions.     

Eccentric/concentric training of ankle evertor and dorsiflexors in recreational athletes: Muscle latency and strength

The aim of this study was to investigate the effects of a combined eccentric–concentric exercise program of the ankle evertors and dorsiflexors on the latency time of the peroneus longus and tibialis anterior muscles. Twenty‐four healthy male recreational athletes were admitted to this study and were randomly assigned to either the exercise group (n = 12) or the control group (n = 12). Subjects in the exercise group performed an isokinetic exercise program of the ankle evertors and dorsiflexors in a combined eccentric–concentric mode for 3 days per week for 6 weeks. Before and after the exercise program, muscle reaction times of the peroneus longus and tibialis anterior muscles to sudden supinating maneuvers on a tilting platform, and isokinetic strength of the ankle joint musculature were evaluated. The peroneus longus and tibialis anterior reaction times showed significant (P < 0.01–0.05) reductions following six weeks of intervention in the exercise group. Additionally, eccentric peak torques for the ankle evertor and dorsiflexors represented significant (P < 0.05) increases in the exercise group compared with the control group. The results of this study suggest that it is possible to reduce peroneal and anterior tibial reaction times following a six week eccentric/concentric isokinetic training program in healthy ankles.     

Influence of acute eccentric exercise on the H:Q ratio

The purpose of the present study was to examine the effects of an acute bout of eccentric exercise on maximal isokinetic concentric peak torque (PT) of the leg flexors and extensors and the hamstrings-to-quadriceps (H:Q) strength ratio. Sixteen male (mean±SD: age=20.9±2 years; stature=177.0±4.4 cm; mass=76.8±10.0 kg) volunteers performed maximal, concentric isokinetic leg extension and flexion muscle actions at 60°·sec?-?1 before and after (24-72 h) a bout of eccentric exercise. The eccentric exercise protocol consisted of 4 sets of 10 repetitions for the leg press, leg extension, and leg curl exercises at 120% of the concentric one repetition maximum (1-RM). The results indicated that the acute eccentric exercise protocol resulted in a significant (P<0.05) decrease in isokinetic leg flexion (13-19%) and leg extension (11-16%) PT 24-72 h post-exercise. However, the H:Q ratios were unaltered by the eccentric exercise protocol. These findings suggest that an acute bout of eccentric exercise utilizing both multi - and single - joint dynamic constant external resistance (DCER) exercises results in similar decreases in maximal isokinetic strength of the leg flexors and extensors, but does not alter the H:Q ratio.     

Relationship between post-exercise plasma CK elevation and muscle mass involved in the exercise.

The purpose of this study was to investigate whether a larger post-exercise increase in plasma creatine kinase (CK) activity would be produced when a larger amount of muscle is damaged by eccentric exercise. Twenty-two non-weight trained females were placed into two groups; Group A (n = 12) and Group B (n = 10). Both groups performed 24 maximal eccentric actions of the forearm flexors on each bout. The right and left arm were exercised on the same day for Group A (24 eccentric actions per arm, a total of 48 actions). In contrast, Group B performed 24 actions with either the right or the left arm on the first bout and performed 24 eccentric actions with the opposite arm on the second bout 3-5 weeks later. Blood samples were taken before and for 5 days after each exercise and plasma CK activity was determined. Forearm flexion isometric force (ISO), range of motion evaluated by relaxed elbow joint angle (RANG) and flexed elbow joint angle (FANG), and perceived muscle soreness (SOR) were also examined to indirectly assess muscle damage. All of the muscle damage indicators changed significantly over time (p < 0.01) for both groups, but changes were not significantly different between arms or between groups. Because it seemed that both arms were equally "damaged" for each group, it was expected that Group A (two arms were exercised on the same day) should show an approximate two-fold increase in plasma CK compared to Group B when one arm was exercised on each bout.(ABSTRACT TRUNCATED AT 250 WORDS)     

Exercise-induced muscle damage: absence of adaptive effect after a single session of eccentric isokinetic heavy resistance exercise

BACKGROUND: Unaccustomed eccentric exercise induces muscle damage. A single session of eccentric exercise can induce an "adaptive effect" protecting exercised muscles during several weeks. Our aim was to verify this phenomenon in isokinetic exercise. Tested hypothesis was: the progressive muscle rise in tension due to isokinetic eccentric actions would be insufficient to induce the adaptive effect. METHODS: Experimental design: prospective study. Setting: general community. Participants: six healthy and moderately active (untrained) males (29.1 yr +/- 1.5 SEM). Interventions: subjects performed two isokinetic eccentric exercises (EE1 and EE2) of the quadriceps femoris of both legs (120 degrees.s-1; 8 sets of 15 repetitions) separated by 4 weeks. Measures: type I serum myosin heavy chains (MHC) and creatine kinase concentrations (CK), and rate of perceived soreness (DOMS) were collected before each exercise and on days 1, 2, 4, 6 and 9. RESULTS: Both exercises induced significant (p < 0.01) increases in MHC and CK concentrations, and DOMS score. There was no significant difference between EE1 and EE2, at any measurement time for any parameter. Mean peak values (SEM) were respectively (EE1; EE2): MHC (microU.l-1): 308 (192); 285 (191). CK (U.l-1): 1217 (760); 1297 (1039). DOMS score: 2.67 (0.52); 2.33 (0.52). CONCLUSIONS: The first session of eccentric isokinetic exercise (EE1) had no adaptive effect against muscle damage when an identical session was performed 4 weeks later (EE2). Muscle adaptation could have resulted in increased work production (+10.2%; p < 0.05; from EE1 to EE2).