Maximal Voluntary Concentric Contractions Research Articles

Ischemic Conditioning Reduces Neuromuscular Fatigability During Dynamic Exercise Post Stroke

INTRODUCTION: In addition to baseline muscle weakness, stroke survivors often demonstrate increased neuromuscular fatigability (an acute exercise-induced reduction in power, hereafter referred to as fatigability), which limits endurance during functional tasks. Ischemic conditioning (IC) is a non-invasive and easy-to-administer intervention that can reduce fatigability in stroke survivors during a sustained isometric contraction of their paretic knee extensors. However, IC’s effects on fatigability during dynamic contractions are unknown, despite the greater relevance to everyday activities. Additionally, fatigability is known to be task specific. Thus, the purpose of this study was to quantify the effects of IC on fatigability (percent reduction in power) during dynamic contractions of the paretic knee extensors in stroke survivors. We hypothesized that fatigability would be less after a single session of IC versus IC-sham treatment in stroke survivors. Methods: Eight stroke survivors (66 ± 6 years of age, 6 male) performed 60 maximal voluntary concentric contractions (1 every 4 seconds) with their paretic knee extensors against a resistance of 30% of their maximal voluntary isometric contraction torque through a 60-degree range of motion after receiving a single session of IC and IC-sham treatment on two separate days. IC consisted of 5 sets of 5-minute upper thigh blood flow occlusion at 225 mmHg (25 mmHg for IC-sham) with 5 minutes of no occlusion between each set. The order of the 2 sessions was randomized. All participants visited the laboratory on a different day for functional measurements (Fugl-Meyer Assessment, 10-meter walk test, and 6-minute walk test). Reduction in power was calculated as the difference between the highest average power output from 5 consecutive contractions within the first 15 contractions and the average power output from the last 5 contractions. A paired t-test was used to compare if fatigability during dynamic exercise would differ between the 2 sessions after IC and IC-sham treatment. Pearson correlation was performed to determine the relationship between the difference in fatigability (after IC versus IC-sham treatment) and functional measurements. Results: After a single session of IC treatment, stroke survivors were less fatigable compared to IC-sham treatment (21.9 ± 19.2% power reduction vs. 29.4 ± 19.0%, p = 0.016). Improvement in fatigability after IC versus IC-sham treatment was positively correlated with Fugl-Meyer Assessment lower extremity motor score ( r = 0.82, p = 0.013). CONCLUSION: These preliminary results indicate that IC could serve as a potential intervention to reduce fatigability during dynamic exercise in stroke survivors, especially those who are mildly affected by stroke. Funding Source: American Heart Association Predoctoral Fellowship (903373, ZZ) and Eunice Kennedy Shriver National Institute of Child Health and Human Development R01 Grant (HD099340, AH & MD). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Comparison of the effects of different foam rolling durations on knee extensors function.

Foam rolling (FR) intervention has recently attracted attention in sports and rehabilitation settings. However, the effects of FR using different rolling durations have not been fully clarified. Thus, this study focused on FR durations and examined the acute and prolonged (i.e., 20-min; 40-min, 60-min) effects of different FR intervention durations on maximal voluntary concentric contractions (MVC-CON), knee flexion range of motion (ROM), pain pressure threshold (PPT), and tissue hardness. The participants were 10 male university students (22.5 ± 1.0 years), and the target muscles were the dominant leg knee extensors. Three sets of 60-seconds FR interventions were performed in the randomized crossover trials in each condition. The three intervention conditions were fast (1 rolling/2 s, 30-repetition × 3 sets, 90 repetitions), medium (1 rolling/6 s, 10-repetition × 3 sets, 30 repetitions), and slow speed (1 rolling/12 s, 5-repetition × 3 sets, 15 repetitions). Before as well as immediately, 20-min, 40-min, and 60-min after the interventions, MVC-CON, ROM PPT, and tissue hardness were measured. The results showed no interaction effect in the acute effect but a main effect of time for all variables (p < 0.05). Also, no interaction was observed in prolonged effect, but main effects of time were observed in knee flexion ROM, PPT, and tissue hardness (p < 0.01) but not for MVC-CON. Post-hoc tests showed significant PPT (p < 0.05) and knee flexion ROM (p < 0.01) increases up to 20- and 60-minutes respectively after all interventions. Tissue hardness was significantly (p < 0.01) decreased up to 60-minutes after all interventions. This study showed that the FR intervention changed ROM, PPT, tissue hardness, and MVC-CON regardless of rolling duration and that the effects persisted up to 20-60 minutes.

Immediate Effects of Blood Flow Restriction Combined with Neuromuscular Electrical Stimulation in Female Amateur Football Players: A Pilot Trial

We aimed to investigate the acute effects of blood flow restriction (BFR) combined with neuromuscular electrical stimulation (NMES) on muscle strength, thigh circumference, and knee joint reposition sense in female amateur football players, as well as to determine whether this procedure is safe. Methods: This was a pilot trial. Twenty female amateur football players were randomized into two groups: group 1 (n = 10) received a single NMES session; group 2 (n = 10) received NMES + BFR. The measured variables included maximal voluntary eccentric contraction (MVEC) and maximal voluntary concentric contraction (MVCC), thigh circumference, and knee joint reposition sense test. The type of electrical current used was TENS (symmetrical biphasic rectangular pulse, 350 μs, and 50 Hz), combined simultaneously with active knee extension (75 repetitions in 4 sets, 20% MVCC, 30 s rest between sets), for both groups. Group 2 had BFR added (80% of arterial occlusion pressure). Results: Statistically significant differences (p ≤ 0.05) were obtained for thigh circumference in both groups. The comparison between groups did not show statistically significant differences (p ≤ 0.05) in MVEC, MVCC, thigh circumference, or the knee joint reposition sense test. Conclusions: Both the isolated NMES intervention and its combination with BFR induced immediate changes in thigh circumference without impairing the muscle strength or proprioceptive ability of the football players. However, these results should be interpreted with caution, and future studies including a control group and isolated BFR application are needed.

Effect of CO2 and H2 gas mixture in cold water immersion on recovery after eccentric loading

BackgroundThe findings of previous studies support the efficacy of cold water immersion (CWI) with carbon dioxide (CO2) in enhancing muscle blood flow and maintaining aerobic performance efficiency. We hypothesize that the addition of hydrogen gas (H2), known for its antioxidant properties and role in inflammation regulation, to C-CWI can enhance recovery after eccentric exercise. Subjectsand Methods: Thirty-four healthy subjects performed a knee-extensor eccentric exercise. They were randomly allocated into four groups: control, CWI, CO2-rich CWI (C-CWI), and CO2 + H2 gas mixture CWI (CH-CWI). In the three CWI groups, all subjects were immersed in the appropriate bath at 20 °C for 20 min immediately after 60 repetitions of eccentric exercise. Before exercise and after 48 h of recovery, the subjects' maximal voluntary isometric contraction torque (MVC-ISO), maximal voluntary concentric (MVC-CON) contraction torque, countermovement jump (CMJ) height, knee flexion range of motion (ROM), muscle soreness, and muscle thickness were measured. ResultsIn the CH-CWI group only, the MVC-ISO, CMJ height, and ROM did not decrease significantly post-exercise, whereas all of these decreased in the other three groups. Muscle soreness at palpation, contraction, and stretching significantly increased post-exercise in all groups. Echo intensity and tissue hardness did not increase significantly in the CH-CWI group. ConclusionsCH-CWI stimulated recovery from impairments in MVC-ISO torque, CMJ height, knee-flexion ROM, tissue hardness, and echo intensity. These findings indicate that CH-CWI can promote recovery after eccentric exercise.

Acute Effects of kinesiotaping on Pain and Muscle Strength in Individuals with Anterior Cruciate Ligament Tear

Abstract Objective Limited data are available regarding the effects of application of kinesiology tape (KT) on pain and muscular strength in individuals with complete anterior cruciate ligament (ACL) tear. Thus, we aimed to evaluate the short-term effects of KT on knee pain and maximal strength. Materials and Methods 25 subjects were divided into two groups: a) the control group participants (n=11) were without ACL-tear; and b) the experimental group participants (n=14) were with ACL-tear. Participants in the experimental group were tested under two conditions: with and without KT. Pain was recorded using the visual analog scale, isometric and concentric maximal voluntary contractions (MVCs) were measured using dynamometry, and limb symmetry index was calculated. Results Application of KT causes reduction in pain by 50 % (p&lt;0.05), increases knee flexors and knee extensors isometric MVC and knee extensor concentric MVC at 60°/s angular velocity (p&lt;0.05), and improves limb symmetry (p&lt;0.05), but deficit of MVC as compared to healthy controls is maintained (p&lt;0.05). Conclusions Short-term KT can be an effective tool for decreasing ACL-tear associated pain and muscle weakness.

Muscle- and Region-Specific Associations Between Muscle Size and Muscular Strength During Hip Extension and Knee Flexion in the Hamstrings.

Strength deficits of the hamstrings following sports injuries decrease athletic performance and increase the risk of injury recurrence. Previous studies have shown a high correlation between the muscular strength during hip-extension and knee-flexion and total muscle size of the hamstrings. However, it remains unclear which region of the individual hamstring muscles is closely associated with muscular strength. To investigate the relationship between the size of each region of the individual hamstring muscles and muscular strength during hip extension and knee flexion. Within-subject repeated measures. University laboratory. Twenty healthy young male volunteers who regularly engaged in sports activities. Anatomical cross-sectional areas were acquired from the proximal, middle, and distal regions of the biceps femoris long head, biceps femoris short head, semitendinosus, and semimembranosus. Hip-extension and knee-flexion strength were measured during maximal voluntary isometric and concentric contractions (angular velocities of 60°/s and 180°/s). The anatomical cross-sectional area of the distal regions in biceps femoris long head (r = .525-.642) and semitendinosus (r = .567) were significantly correlated with hip-extension strength under all conditions and only at an angular velocity of 180°/s, respectively. Meanwhile, anatomical cross-sectional areas of the distal regions in biceps femoris short head (r = .587-.684) and semimembranosus (r = .569-.576) were closely associated with knee-flexion strength under all conditions. These results suggest that muscle size in the distal regions of biceps femoris long head and semitendinosus greatly contributes to the production of hip-extension strength, whereas that of biceps femoris short head and semimembranosus significantly contributes to the generation of knee-flexion strength. These findings could be useful for designing training and rehabilitation programs to efficiently improve strength deficits following sports injuries such as strain injury and anterior cruciate ligament tears.

Choline-Based Multi-Ingredient Supplementation Can Improve Explosive Strength during a Fatiguing Task.

Various choline-based multi-ingredient supplementations (CMS) have been suggested in the current market, but the research is limited. The purpose of this study was to investigate the acute effect of a CMS on physical performance. Fourteen male college football players (20.4 ± 1.0 years) participated in a randomized double-blind crossover experiment separated by 7 days. Subjects were given a CMS or a placebo 60 min before physical performance testing measures, including maximum vertical jumps, maximum voluntary isometric contractions (MVIC), maximal voluntary concentric contractions (MVCC), and fatiguing contractions. Four MVICs and seven sets of two MVCCs at various loads (1 N·m to 60% MVIC torque) were performed with the knee extensor muscles while seated on a dynamometer before and after the fatiguing tasks. During the fatiguing tasks, 120 MVCCs (4 sets × 30 reps) were performed with a load equivalent to 20% MVIC. Twitch interpolation technique was used to assess muscle contractile properties and voluntary activation. No significant differences were seen at baseline between sessions for all testing measures including vertical jump height, strength, power, muscle contractile properties and voluntary activation. Rate of torque development and impulse was higher in supplemental session compared to control session throughout the fatiguing contractions (p = 0.018, p < 0.001, respectively). Acute CMS can improve explosive strength by delaying the onset of fatigue.

Comparison Between Foam Rolling With and Without Vibration on Passive and Active Plantar Flexor Muscle Properties.

Nakamura, M, Sato, S, Kiyono, R, Yoshida, R, Yasaka, K, Yahata, K, and Konrad, A. Comparison between foam rolling with and without vibration on passive and active plantar flexor muscle properties. J Strength Cond Res XX(X): 000-000, 2021-Although foam rolling interventions with and without vibration have been used to increase flexibility in the field of sports, their effects on passive and active properties remain unclear. Hence, this study aimed to investigate the effects of foam rolling interventions on range of motion (ROM), shear elastic modulus, plantar flexor muscle strength, and jump performance. This randomized, controlled, crossover study included 16 healthy male subjects who visited the laboratory 3 times (control condition, foam rolling condition, and vibration foam rolling condition), each with an interval of >72 hours. In both foam rolling and vibration foam rolling conditions, subjects were instructed to perform 60-second bouts of intervention for 3 sets, with 30-second rest between each set. In the vibration foam rolling condition, the intensity of vibration was set at a frequency of 48 Hz. Dorsiflexion (DF) ROM, shear elastic modulus, plantar flexor muscle strength, and drop jump height were determined before and after the rolling intervention. Our results showed a similar increase in dorsiflexion range of motion (p < 0.01, d = 0.51; p < 0.01, d = 0.65, respectively) and passive torque at dorsiflexion range of motion (p = 0.02, d = 0.51 and p < 0.01, d = 0.65, respectively) after foam rolling and vibration foam rolling. Medial gastrocnemius shear elastic modulus decreased only after vibration foam rolling (p < 0.01, d = 0.44). No significant main effects of time were observed in maximal voluntary isometric contraction torque (F = 2.0, p = 0.15, = 0.119) and drop jump height (F = 1.5, p = 0.24, = 0.091) after both interventions. Maximal voluntary concentric contraction torque showed a significant main effect of time (F = 7.59, p = 0.02, = 0.336). However, only after foam rolling, the maximal voluntary concentric contraction torque significantly decreased (p = 0.01, d = 0.39). Our results suggest that vibration foam rolling effectively alters passive muscle properties without decreasing muscle strength and performance.

Effect of Leg Eccentric Exercise on Muscle Damage of the Elbow Flexors after Maximal Eccentric Exercise.

The magnitude of muscle damage induced by maximal eccentric exercise is attenuated when the same exercise is repeated by homologous muscle of the ipsilateral or contralateral limb. It is not known if the muscle damage-protective effect is also transferred to nonhomologous muscles. The present study investigated the effects of unilateral knee extensor (KE) or flexor (KF) eccentric exercise on muscle damage induced by elbow flexor (EF) eccentric exercise of the ipsilateral or contralateral side. Young healthy sedentary men were assigned to four experimental groups (n = 13 per group) that performed five sets of six maximal eccentric contractions (MaxEC) of the KE or KF of the same or opposite side of the arm that performed MaxEC of the EF 1 wk later, and a control group that performed two bouts of MaxEC of the EF using a different arm for each bout separated by 1 wk. Changes in several indirect muscle damage markers were compared among the groups by mixed-design, two-way ANOVA. Changes in maximal voluntary concentric contraction torque, range of motion, muscle soreness, and plasma creatine kinase activity after KE or KF MaxEC were not different (P > 0.05) between legs, but greater (P < 0.05) after KF than KE MaxEC. The changes in the variables after EF MaxEC in the experimental groups were not different (P > 0.05) from the first bout of the control group but larger (P < 0.05) than the second bout of the control group, and no differences between the ipsilateral and contralateral sides were evident. These results showed that no protective effect on EF MaxEC was conferred by the leg exercises, suggesting that muscle damage protection was not transferred from KE or KF to EF.

Effects of trunk extensor eccentric exercise on lipid profile and glycaemic response

ObjectivesA number of previous studies reported physiological responses and adaptations after eccentric muscle contraction of limb muscles. In contrast, no study has determined physiological response after eccentric contraction of trunk...

Supraspinal Control of Recurrent Inhibition during Anisometric Contractions.

Increase in recurrent inhibition was observed during eccentric compared with isometric and concentric maximal voluntary contractions but the neural mechanisms involved in this specific control of the Renshaw cell activity are unknown. This study was designed to investigate the supraspinal control of the recurrent inhibition during anisometric contractions of the plantar flexor muscles. To that purpose, the paired Hoffmann-reflex (H-reflex) technique permitted to assess changes in homonymous recurrent pathway by comparing the modulations of test and conditioning H-reflexes (H' and H1, respectively) in the soleus (SOL) muscle during maximal and submaximal isometric, concentric and eccentric contractions. Submaximal contraction intensity was set at 50% of the SOL electromyographic activity recorded during maximal isometric contraction. Fourteen volunteer subjects participated in an experimental session designed to assess the activity of the recurrent inhibition pathway. The results indicate that the amplitude of H1 normalized to the maximal M-wave were similar (P > 0.05) regardless of the muscle contraction type and intensity. Whatever the contraction intensity, the ratio between H' and H1 amplitudes was significantly decreased (P < 0.05) during eccentric compared with isometric and concentric contractions. Furthermore, this ratio was significantly smaller (P < 0.05) during submaximal compared with maximal contractions whatever the muscle contraction type. Together, the current results confirm the supraspinal control of the Renshaw cell activity when muscle contraction intensity is modulated and show that this control remains similar for isometric, concentric and eccentric contractions. Data further suggest that recurrent inhibition pathway may serve as variable gain regulator at motoneuronal level to improve resolution in the control of motor output for the SOL during eccentric contractions.

Changes in central and peripheral neuromuscular fatigue indices after concentric versus eccentric contractions of the knee extensors.

To better understand neuromuscular characteristics of eccentric exercise-induced muscle damage, this study compared between concentric (CONC) and eccentric (ECC) exercises of knee extensor muscles, and the first (ECC1) and second bouts of the eccentric exercise (ECC2) for central and peripheral parameters associated with neuromuscular fatigue. Twelve young men performed three exercise bouts separated by at least 1week between CONC and ECC1, and 2weeks between ECC1 and ECC2. In each exercise, maximal voluntary concentric or eccentric contractions of the knee extensors were performed until a reduction in maximal voluntary isometric contraction (MVC) torque of at least 40% MVC was achieved immediately post-exercise. MVC torque, central (voluntary activation and normalised electromyographic activity), and peripheral neuromuscular indices (evoked torque and M-wave amplitude), and muscle soreness were assessed before (PRE), immediately after (POST), 1h (1H), and 1-4 days after exercise (D1, D2, D3, and D4). MVC torque decreased at only POST for CONC (- 52.8%), but remained below the baseline at POST (- 48.6%), 1H (- 34.1%), and D1-D4 (- 34.1 to - 18.2%) after ECC1, and at POST (- 45.2%), 1H (- 24.4%) and D1 (- 13.4%) after ECC2 (p < 0.05). Voluntary activation decreased immediately after ECC1 (- 21.6%) and ECC2 (- 21.1%), but not after CONC. Electrically evoked torques decreased similarly at POST and 1H for the three conditions, but remained below the baseline at D1 only post-ECC1. These results showed that both central and peripheral factors contributed to the MVC decrease after ECC1 and ECC2, but the decrease was mainly due to peripheral factors after CONC.

Muscle damage protective effect by two maximal isometric contractions on maximal eccentric exercise of the elbow flexors of the contralateral arm.

Muscle damage after 30 maximal eccentric contractions of the elbow flexors (30MVEC) is reduced when the same exercise is performed by the opposite arm, and when two maximal voluntary isometric contractions at a long muscle length (2MVIC) are performed prior to 30MVEC by the same arm. This study investigated the hypothesis that 2MVIC would attenuate muscle damage after 30MVEC performed by the opposite arm. Untrained young (20-25years) men were placed into 1 of 4 experimental groups that performed 2MVIC at 1 (1d), 2 (2d), 4 (4d), or 7days (7d) before 30MVEC by the opposite arm, or one control group that performed 30MVEC only (n=13/group). Changes in indirect muscle damage markers after 30MVEC were compared among the groups by mixed-design two-way ANOVA. Maximal voluntary concentric contraction torque, range of motion, plasma creatine kinase activity, and muscle soreness did not change significantly after 2MVIC. Changes in these variables after 30MVEC were smaller (P<.05) for 1d (eg, peak soreness: 45±21mm) and 2d groups (46±20mm) than control group (66±18mm), without significant differences between 1d and 2d groups. No significant differences in the changes were found among 4d, 7d, and control groups, except for soreness showing smaller (P<.05) increases for 4d group (54±19mm) than 7d (62±17mm) and control groups. These results supported the hypothesis and showed that muscle damage induced by 30MVEC was reduced by 2MVIC performed 1-2days prior to 30MVIC by the contralateral arm.

Influence of Maturation Status on Eccentric Exercise-Induced Muscle Damage and the Repeated Bout Effect in Females.

This study compared changes in indirect muscle damage markers, proprioception and arterial stiffness after elbow flexor eccentric exercise between pre-pubescent (9–10 y), pubescent (14–15 y), and post-pubescent (20–24 y) healthy, untrained females (n = 13/group). The maturation of the participants was confirmed by the hand bone age. All participants performed two bouts of 30 sub-maximal eccentric contractions (EC1, EC2) using a dumbbell set at 60% of pre-exercise maximal voluntary isometric elbow flexion strength at 90°. Changes in maximal voluntary concentric contraction (MVC) torque, muscle soreness (SOR), plasma creatine kinase activity, proprioception (position sense, joint reaction angle) and arterial stiffness (carotid-femoral pulse-wave velocity: cfPWV) before to 5 days after EC1 and EC2 were compared among groups by a mixed-design two-way ANOVA. Pre-exercise MVC torque and cfPWV were smaller (P < 0.05) for the pre-pubescent (MVC: 10.0 ± 0.9 Nm, cfPWV: 903 ± 60 cm/s) and the pubescent (14.3 ± 1.1 Nm, 967 ± 61 cm/s) than the post-pubescent (19.1 ± 1.4 Nm, 1,103 ± 73 cm/s). Changes in all variables after EC1 were smaller (P < 0.05) for the pre-pubescent (e.g., MVC at 1 d post-exercise: −10 ± 6%, peak SOR: 5 ± 2 mm) than the pubescent (−15 ± 9%, 12 ± 6 mm) and the post-pubescent (−25 ± 7%, 19 ± 13 mm). After EC2, changes in all variables were smaller (P < 0.05) than those after EC1 for all groups (e.g., MVC at 1 d post-exercise, pre-pubescent: −4 ± 6%, pubescent: −9 ± 4%, post-pubescent: −14 ± 5%; peak SOR: 3 ± 2, 7 ± 3, 11 ± 6 mm), but the magnitude of the repeated bout effect was not different (P > 0.05) among the groups. These results show that the extents of muscle damage, and proprioception and arterial stiffness changes after eccentric exercise are greater at later stages of maturation, but the repeated bout effect is not affected by maturation.

Post Activation Potentiation and Concentric Contraction Performance: Effects on Rate of Torque Development, Neuromuscular Efficiency, and Tensile Properties.

Gago, P, Zoellner, A, Cezar, J, and Ekblom, MM. Post activation potentiation and concentric contraction performance: effects on rate of torque development, neuromuscular efficiency and tensile properties. J Strength Cond Res 34(6): 1600-1608, 2020-This study investigated how a 6-second maximal voluntary isometric contraction (MVIC) conditioning affected plantar flexor twitch rate of torque development (RTDTW), as well as peak torque (PTCC) and rate of torque development (RTDCC) of maximal voluntary concentric contractions (MVCC) performed at 60°·s. RTDCC and normalized triceps surae electromyography signals (EMGTS) were measured during different phases of contraction. In addition, muscle tendon unit passive stiffness index (SI) calculated from the torque-angle relation was measured after each MVCC. Enhancements were found in the RTDTW immediately (by 59.7%) and up to 480 seconds (by 6.0%) after MVIC (p < 0.05). RTDCC during the 100-200 ms, 50-200 ms, and 0-200 ms phases and PTCC were enhanced (by 5.7-9.5%) from 90 to 300 seconds after conditioning (p < 0.05). Neuromuscular efficiency increased (decreased EMGTS/RTDCC) in the 50-200 ms and 0-200 ms phases by 8.8-12.4%, from 90 to 480 seconds after MVIC (p < 0.05). No significant changes were found in the SI or in RTDCC during the 50-100 ms phase, suggesting that the enhancements reported reflect mainly contractile rather than neural or tensile mechanisms. PAP effects on PTCC and RTDCC were significant and more durable at a lower velocity than previously reported. Enhancement in RTDCC and neuromuscular efficiency were found to be more prominent in later phases (>100 ms) of the MVCC. This suggests that enhanced contractile properties, attained through MVIC, benefit concentric contraction performance.

Low-intensity elbow flexion eccentric contractions attenuate maximal eccentric exercise-induced muscle damage of the contralateral arm

ObjectivesThe magnitude of muscle damage induced by maximal eccentric contractions (MaxEC) of the elbow flexors (EF) is reduced when it is preceded by low-intensity (10% of maximal voluntary isometric contraction strength) eccentric contractions (10%EC) of the same muscle, or by MaxEC of the opposite EF. This study investigated whether 10%EC would reduce the magnitude of muscle damage after MaxEC performed by the opposite arm. DesignComparison among 6 groups for changes in indirect markers of muscle damage. MethodYoung (21.0±1.8years) untrained men were assigned to five experimental groups (n=13/group) that performed 30, 10%EC followed by 30 MaxEC of the other arm performed at either 1 (1d), 2 (2d), 7 (1wk), 14 (2wk) or 21days (3wk) later, and one control group that performed 30 MaxEC without 10%EC (n=13). Changes in several indirect markers of muscle damage after MaxEC were compared among the groups by mixed-design two-way ANOVAs. ResultsNo significant changes in maximal voluntary concentric contraction torque, plasma creatine kinase activity and muscle soreness were evident after 10%EC. Changes in these variables after MaxEC were smaller (p<0.05) for the 1d, 2d and 1wk groups than control group, without significant differences between the 1d, 2d and 1wk groups. No significance differences in the changes were evident among the 2wk, 3wk and control groups, except for muscle soreness showing smaller (p<0.05) increases for the 2wk and 3wk groups than control group. ConclusionsThese results showed that 10%EC conferred muscle damage protection to the contralateral arm that performed MaxEC.

Leg Blood Flow and Fatigability In People With Type 2 Diabetes

We have previously demonstrated that people with type 2 diabetes mellitus (T2D) have greater fatigability of the knee extensor muscles during a dynamic fatiguing contraction due to impairments within the skeletal muscle; however, the precise mechanism(s) are unknown. PURPOSE: To determine if impairments in leg blood flow are associated with greater fatigability of the knee extensor muscles during a dynamic fatiguing contraction in men and women with T2D. METHODS: 5 individuals with non-insulin dependent T2D (60 - 70 years; 3 women) with no signs of diabetic neuropathy were matched based on age, BMI and physical activity with four non-diabetic controls (CON) (60 - 68 years; 2 women). Physical activity was assessed over four days with a tri-axial accelerometer. To assess fatigability, participants performed a 6-minute single-limb dynamic fatiguing contractions with the knee extensors while seated at 90° of hip and knee flexion. 120 maximal voluntary concentric contractions (MVCCs) were performed with a load equivalent to 20% maximal voluntary isometric contraction torque through a 90° range of motion. Doppler ultrasonograpy was used to assess femoral artery diameter and pulse wave blood velocity before and immediately after the dynamic fatiguing contraction. RESULTS: The reduction in MVCC power was greater for T2D (40.5 ± 17.6%) compared with CON (31.3 ± 20.8%, P < 0.05) as assessed at the end of exercise. T2D and CON both demonstrated similar increases in leg blood flow after the dynamic fatiguing contraction (71.7 ± 41.1% vs. 69.0 ± 37.3%, respectively; p > 0.05). However, greater reductions in MVCC power (i.e. greater fatigability) was associated with lower blood flow following dynamic fatiguing contractions (p = 0.034, r = 0.633). CONCLUSIONS: Greater fatigability of the knee extensor muscles during dynamic fatiguing contractions was associated with lower blood flow. Impaired blood flow responses to exercise may limit exercise performance among T2D, and this work highlights the need for future studies that examine skeletal muscle perfusion during dynamic exercise in people with T2D. Supported by Marquette University Way Klingler Research Fellowship to SKH

Sex differences in neuromuscular function after repeated eccentric contractions of the knee extensor muscles.

This study examined the mechanisms for force and power reduction during and up to 48h after maximal eccentric contractions of the knee extensor muscles in young men and women. 13 men (22.8 ± 2.6years) and 13 women (21.6 ± 2.2years) performed 150 maximal effort eccentric contractions (5 sets of 30) with the knee extensor muscles at 60°s-1. Maximal voluntary isometric contractions (MVIC) and maximal voluntary concentric contractions (MVCC) were performed before and after the 150 eccentric contractions. The MVCCs involved a set of two isokinetic contractions at 60°s-1 and sets of isotonic contractions performed at seven different resistance loads (1Nm, 10, 20, 30, 40, 50, and 60% MVIC). Electrical stimulation was used during the MVICs and at rest to determine changes in voluntary activation and contractile properties. At baseline, men were stronger than women (MVIC: 276 ± 48 vs. 133 ± 37Nm) and more powerful (MVCC: 649 ± 77 vs. 346 ± 78W). At termination of the eccentric contractions, voluntary activation, resting twitch amplitude, and peak power during concentric contractions at the seven loads and at 60°s-1 decreased (P < 0.05) similarly in the men and women. At 48h post-exercise, the MVIC torque, power (for loads ≥20-60% MVIC), and voluntary activation remained depressed (P < 0.05), but the resting twitch had returned to baseline (P > 0.05) with no sex differences. Central mechanisms were primarily responsible for the depressed maximal force production up to 48h after repeated eccentric contractions of the knee extensors and these mechanisms were similar in men and women.

Protective effect by maximal isometric contractions against maximal eccentric exercise-induced muscle damage of the knee extensors

ABSTRACTThis study investigated whether maximal voluntary isometric contractions (MVIC) performed before maximal eccentric contractions (MaxEC) would attenuate muscle damage of the knee extensors. Untrained men were placed to an experimental group that performed 6 sets of 10 MVIC at 90° knee flexion 2 weeks before 6 sets of 10 MaxEC or a control group that performed MaxEC only (n = 13/group). Changes in muscle damage markers were assessed before to 5 days after each exercise. Small but significant changes in maximal voluntary concentric contraction torque, range of motion (ROM) and plasma creatine kinase (CK) activity were evident at immediately to 2 days post-MVIC (p < 0.05), but other variables (e.g. thigh girth, myoglobin concentration, B-mode echo intensity) did not change significantly. Changes in all variables after MaxEC were smaller (p < 0.05) by 45% (soreness)–67% (CK) for the experimental than the control group. These results suggest that MVIC conferred potent protective effect against MaxEC-induced muscle damage.

Muscle activation varies with contraction mode in human spinal cord injury.

To better understand volitional force generation after chronic incomplete spinal cord injury (SCI), we examined muscle activation during single and repeated isometric, concentric, and eccentric knee extensor (KE) maximal voluntary contractions (MVCs). Torque and electromyographic (EMG) activity were recorded during single and repeated isometric and dynamic KE MVCs in 11 SCI subjects. Central activation ratios (CARs) were calculated for all contraction modes in SCI subjects and 11 healthy controls. SCI subjects generated greater torque, KE EMG, and CARs during single eccentric vs. isometric and concentric MVCs (all P < 0.05). Torque and EMG remained similar during repeated eccentric MVCs; however, both increased during repeated isometric (>25%) and concentric (>30%) MVCs. SCI subjects demonstrated greater muscle activation during eccentric MVCs vs. isometric and concentric MVCs. This pattern of activation contrasts with the decreased eccentric activation demonstrated by healthy controls. Such information may aid development of novel rehabilitation interventions.