Effects of concentric and eccentric training on muscle strength, cross-sectional area, and neural activation

Higbie, Elizabeth J., Kirk J. Cureton, Gordon L. Warren III,and Barry M. Prior. Effects of concentric and eccentric trainingon muscle strength, cross-sectional area, and neural activation.J. Appl. Physiol. 81(5):2173-2181, 1996.We compared the effects of concentric (Con) andeccentric (Ecc) isokinetic training on quadriceps muscle strength,cross-sectional area, and neural activation. Women (age 20.0 ± 0.5 yr) randomly assigned to Con training (CTG;n = 16), Ecc training (ETG;n = 19), and control (CG;n = 19) groups were tested before andafter 10 wk of unilateral Con or Ecc knee-extension training. Averagetorque measured during Con and Ecc maximal voluntary knee extensions increased 18.4 and 12.8% for CTG, 6.8 and 36.2% for ETG, and 4.7 and1.7% for CG, respectively. Increases by CTG and ETG were greater than for CG (P < 0.05). ForCTG, the increase was greater when measured with Con than with Ecctesting. For ETG, the increase was greater when measured with Ecc thanwith Con testing. The increase by ETG with Ecc testing was greater thanthe increase by CTG with Con testing. Corresponding changes in theintegrated voltage from an electromyogram measured during strengthtesting were 21.7 and 20.0% for CTG, 7.1 and 16.7% for ETG, and8.0 and 9.1% for CG. Quadriceps cross-sectional areameasured by magnetic resonance imaging (sum of 7 slices) increased morein ETG (6.6%) than in CTG (5.0%) (P < 0.05). We conclude that Ecc is more effective than Con isokinetictraining for developing strength in Ecc isokinetic muscle actions andthat Con is more effective than Ecc isokinetic training for developingstrength in Con isokinetic muscle actions. Gains in strength consequentto Con and Ecc training are highly dependent on the muscle action usedfor training and testing. Muscle hypertrophy and neural adaptationscontribute to strength increases consequent to both Con and Ecctraining.

     

Specific effects of eccentric and concentric training on muscle strength and morphology in humans

The purpose of this study was to compare pure eccentric and concentric isokinetic training with respect to their possible specificity in the adaptation of strength and morphology of the knee extensor muscles. Ten moderately trained male physical education students were divided into groups undertaking eccentric (ETG) and concentric (CTG) training. They performed 10 weeks of maximal isokinetic (90 degrees x s(-1)) training of the left leg, 4x10 repetitions - three times a week, followed by a second 10-week period of similar training of the right-leg. Mean eccentric and concentric peak torques increased by 18% and 2% for ETG and by 10% and 14% for CTG, respectively. The highest increase in peak torque occurred in the eccentric 90 degrees x s(-1) test for ETG (35%) whereas in CTG strength gains ranged 8%-15% at velocities equal or lower than the training velocity. Significant increases in strength were observed in the untrained contra-lateral leg only at the velocity and mode used in ipsilateral training. Cross-sectional area of the quadriceps muscle increased 3%-4% with training in both groups, reaching statistical significance only in ETG. No major changes in muscle fibre composition or areas were detected in biopsies from the vastus lateralis muscle for either leg or training group. In conclusion, effects of eccentric training on muscle strength appeared to be more mode and speed specific than corresponding concentric training. Only minor adaptations in gross muscle morphology indicated that other factors, such as changes in neural activation patterns, were causing the specific training-induced gains in muscle strength.     

Non-uniform muscle adaptations to eccentric exercise and the implications for training and sport

Due to the variations in morphological and architectural characteristics of fibers within a skeletal muscle, regions of a muscle may be differently affected by eccentric exercise. Although eccentric exercise may be beneficial for increasing muscle mass and can be beneficial for the treatment of tendinopathies, the non-uniform effect of eccentric exercise results in regional muscle damage and as a consequence, non-uniform changes in muscle activation. This regional muscle weakness can contribute to muscle strength imbalances and may potentially alter the load distribution on joint structures, increasing the risk of injury. In this brief review, the non-uniform effects of eccentric exercise are reviewed and their implications for training and sport are considered.     

Effects of eccentric exercise on microcirculation and microvascular oxygen pressures in rat spinotrapezius muscle.

A single bout of eccentric exercise results in muscle damage, but it is not known whether this is correlated with microcirculatory dysfunction. We tested the following hypotheses in the spinotrapezius muscle of rats either 1 (DH-1; n = 6) or 3 (DH-3; n = 6) days after a downhill run to exhaustion (90-120 min; -14 degrees grade): 1) in resting muscle, capillary hemodynamics would be impaired, and 2) at the onset of subsequent acute concentric contractions, the decrease of microvascular O(2) pressure (Pmv(o(2))), which reflects the dynamic balance between O(2) delivery and O(2) utilization, would be accelerated compared with control (Con, n = 6) rats. In contrast to Con muscles, intravital microscopy observations revealed the presence of sarcomere disruptions in DH-1 and DH-3 and increased capillary diameter in DH-3 (Con: 5.2 +/- 0.1; DH-1: 5.1 +/- 0.1; DH-3: 5.6 +/- 0.1 mum; both P < 0.05 vs. DH-3). At rest, there was a significant reduction in the percentage of capillaries that sustained continuous red blood cell (RBC) flux in both DH running groups (Con: 90.0 +/- 2.1; DH-1: 66.4 +/- 5.2; DH-3: 72.9 +/- 4.1%, both P < 0.05 vs. Con). Capillary tube hematocrit was elevated in DH-1 but reduced in DH-3 (Con: 22 +/- 2; DH-1: 28 +/- 1; DH-3: 16 +/- 1%; all P < 0.05). Although capillary RBC flux did not differ between groups (P > 0.05), RBC velocity was lower in DH-1 compared with Con (Con: 324 +/- 43; DH-1: 212 +/- 30; DH-3: 266 +/- 45 mum/s; P < 0.05 DH-1 vs. Con). Baseline Pmv(O(2)) before contractions was not different between groups (P > 0.05), but the time constant of the exponential fall to contracting Pmv(O(2)) values was accelerated in the DH running groups (Con: 14.7 +/- 1.4; DH-1: 8.9 +/- 1.4; DH-3: 8.7 +/- 1.4 s, both P < 0.05 vs. Con). These findings are consistent with the presence of substantial microvascular dysfunction after downhill eccentric running, which slows the exercise hyperemic response at the onset of contractions and reduces the Pmv(O(2)) available to drive blood-muscle O(2) delivery.     

Effects of endurance exercise training on muscle glycogen accumulation in humans.

The purpose of this investigation was to determine whether endurance exercise training increases the ability of human skeletal muscle to accumulate glycogen after exercise. Subjects (4 women and 2 men, 31 +/- 8 yr old) performed high-intensity stationary cycling 3 days/wk and continuous running 3 days/wk for 10 wk. Muscle glycogen concentration was measured after a glycogen-depleting exercise bout before and after endurance training. Muscle glycogen accumulation rate from 15 min to 6 h after exercise was twofold higher (P < 0.05) in the trained than in the untrained state: 10.5 +/- 0.2 and 4.5 +/- 1.3 mmol. kg wet wt(-1). h(-1), respectively. Muscle glycogen concentration was higher (P < 0.05) in the trained than in the untrained state at 15 min, 6 h, and 48 h after exercise. Muscle GLUT-4 content after exercise was twofold higher (P < 0.05) in the trained than in the untrained state (10.7 +/- 1.2 and 4.7 +/- 0.7 optical density units, respectively) and was correlated with muscle glycogen concentration 6 h after exercise (r = 0.64, P < 0.05). Total glycogen synthase activity and the percentage of glycogen synthase I were not significantly different before and after training at 15 min, 6 h, and 48 h after exercise. We conclude that endurance exercise training enhances the capacity of human skeletal muscle to accumulate glycogen after glycogen-depleting exercise.     

Gender differences in muscle inflammation after eccentric exercise.

Unaccustomed exercise is followed by delayed-onset muscle soreness and morphological changes in skeletal muscle. Animal studies have demonstrated that women have an attenuated response to muscle damage. We studied the effect of eccentric exercise in untrained male (n = 8) and female (n = 8) subjects using a unilateral exercise design [exercise (Ex) and control (Con) legs]. Plasma granulocyte counts [before (Pre) and 48 h after exercise (+48h)] and creatine kinase activity [Pre, 24 h after exercise (+24h), +48h, and 6 days after exercise (+6d)] were determined before (Pre) and after (+24h, +48h, +6d) exercise, with biopsies taken from the vastus lateralis of each leg at +48h for determination of muscle damage and/or inflammation. Plasma granulocyte counts increased for men and decreased for women at +48h (P < 0.05), and creatine kinase activity increased for both genders at +48h and +6d (P < 0.01). There were significantly greater areas of both focal (P < 0.001) and extensive (P < 0.01) damage in the Ex vs. Con leg for both genders, which was assessed by using toluidine blue staining. The number of leukocyte common antigen-positive cells/mm(2) tissue increased with exercise (P < 0.05), and men tended to show more in their Ex vs. Con leg compared with women (P = 0.052). Men had a greater total (Ex and Con legs) number of bcl-2-positive cells/mm(2) tissue vs. women (P < 0.05). Atrophic fibers with homogeneous bcl-2-positive staining were seen only in men (n = 3). We conclude that muscle damage is similar between genders, yet the inflammatory response is attenuated in women vs. men. Finally, exercise may stimulate the expression of proteins involved in apoptosis in skeletal muscle.     

Effects of a shoulder injury prevention strength training program on eccentric external rotator muscle strength and glenohumeral joint imbalance in female overhead activity athletes

Imbalance of the eccentrically-activated external rotator cuff muscles versus the concentrically-activated internal rotator cuff muscles is a primary risk factor for glenohumeral joint injuries in overhead activity athletes. Nonisokinetic dynamometer based strength training studies, however, have focused exclusively on resulting concentric instead of applicable eccentric strength gains of the external rotator cuff muscles. Furthermore, previous strength training studies did not result in a reduction in glenoumeral joint muscle imbalance, thereby suggesting that currently used shoulder strength training programs do not effectively reduce the risk of shoulder injury to the overhead activity athlete. Two collegiate women tennis teams, consisting of 12 women, participated in this study throughout their preseason training. One team (n = 6) participated in a 5-week, 4 times a week, external shoulder rotator muscle strength training program next to their preseason tennis training. The other team (n = 6) participated in a comparable preseason tennis training program, but did not conduct any upper body strength training. Effects of this strength training program were evaluated by comparing pre- and posttraining data of 5 maximal eccentric external immediately followed by concentric internal contractions on a Kin-Com isokinetic dynamometer (Chattecx Corp., Hixson, Tennessee). Overall, the shoulder strength training program significantly increased eccentric external total work without significant effects on concentric internal total work, concentric internal mean peak force, or eccentric external mean peak force. In conclusion, by increasing the eccentric external total exercise capacity without a subsequent increase in the concentric internal total exercise capacity, this strength training program potentially decreases shoulder rotator muscle imbalances and the risk for shoulder injuries to overhead activity athletes.     

Effect of resistance exercise training on cortical and cancellous bone in mature male rats

Westerlind, Kim C., James D. Fluckey, Scott E. Gordon,William J. Kraemer, Peter A. Farrell, and Russell T. Turner.Effect of resistance exercise training on cortical and cancellousbone in mature male rats. J. Appl.Physiol. 84(2): 459-464, 1998.The effect ofresistance training on tibial cancellous and cortical bone wasevaluated in rats by using static histomorphometry and Northernanalysis. Five-month-old male Sprague-Dawley rats were randomlyassigned to exercise (Ex; n = 8) orcontrol (Con; n = 4) groups. Animalswere operantly conditioned to press two levers, facilitating fullextension and flexion of the hindlimbs ("squats"), while wearingan unweighted vest. After an 8-wk familiarization period, Ex animalsperformed 3 sessions/wk for 17-19 sessions with progressivelyincreased amounts of weight applied to the vest. Con rats completed thesame exercise protocol without applied resistance. No difference incross-sectional, medullary, or cortical bone area was observed betweenEx and Con rats in the tibial diaphysis. In contrast, the cancellousbone area in the proximal tibial metaphysis was significantly larger intrained rats. Trabecular number, trabecular thickness, and thepercentage of cancellous bone covered by osteoid were significantlygreater in the Ex animals compared with Con animals. In addition,steady-state mRNA levels for osteocalcin for the Ex group were 456%those expressed in the Con group. The data demonstrate that resistancetraining increases cancellous bone area in sexually mature male ratsand suggest that it does so, in part, by stimulating bone formation.

     

Lovastatin use and muscle damage in healthy volunteers undergoing eccentric muscle exercise.

We did a double-blind, placebo-controlled crossover study of 10 healthy young men taking no medications to determine if ingesting lovastatin is associated with more severe muscle damage after exercise. Five men in the first group took 40 mg of lovastatin daily for 30 days while those in the second group took an identical-appearing placebo. Each volunteer then walked downhill on a -14-degree incline on a treadmill at 3 km per hour for an hour. After a 2-week rest, the subjects were crossed over. Serial serum creatine kinase activity was measured immediately before and 8, 24, 48, 72, 120, and 144 hours after each treadmill session. With each subject serving as his own control, peak mean serum creatine kinase activity (/+- SEM) following treadmill after lovastatin therapy was similar to that following placebo (168.4 +/- 25.8 U per liter versus 146.7 +/- 14.7 U per liter, respectively [P = .9]). With an alpha value of .05, we had greater than a 99% chance of detecting a difference in the rise of serum creatine kinase activity of 200 U per liter between groups. Our data suggest that lovastatin is not an independent risk factor for developing exercise-induced muscle damage using this model of exercise in our study population.     

Effects of an eccentric exercise session short-term recovery of muscle contractility

Short term effects of 5 sets of 10 maximal eccentric contractions of the elbow flexors, performed using an isokinetic ergometer, were studied. Maximal eccentric, isometric, concentric torque, myoelectrical activity of biceps and triceps brachii, voluntary activation, M-wave amplitude, as well as twitch and maximal contraction and relaxation velocities were measured before (Control), 2 minutes after (Post), 24 hours (Post24 h) and 48 hours (Post48 h) after the exercise session. Torque significantly decreased over the recovery period, whatever the contraction type, excepted concentric torque assessed at 240 degrees.s-1 which recovered its Control value at Post48 h. Activation level significantly decreased at Post (p < 0.05) and returned to its Control value at Post24 h. Twitch, as well as maximal contraction and relaxation velocities had significantly declined among the experimental procedure (p < 0.01). M-wave amplitude was not modified after the exercise. These results indicate that, over a 48 hour rest period, torque decrement following a maximal eccentric exercise session should mainly be due to a failure of the peripheral part of the neuromuscular system, and force recovery should closely be linked to the developed force value.     

Effects of age and regular exercise on muscle strength and endurance

Twenty male and 20 female non-professional tennis players were classified into two different age groups (n = 10 per group): young active men (30.4 +/- 3.3 years), young active women (27.5 +/- 4.3 years), elderly active men (64.4 +/- 3.7 years), and elderly active women (65.3 +/- 4.5 years). These individuals were matched (n = 10 per group) according to sex, age, height and mass to sedentary individuals of the same socio-economical background: young sedentary men (29.2 +/- 3.4 years), young sedentary women (25.6 +/- 4.4 years), elderly sedentary men (65.2 +/- 3.2 years) and elderly sedentary women (65.6 +/- 4.4 years). An isokinetic dynamometer was used to measure the strength of the knee extensors and flexors (two separate occasions) and the endurance of the extensors. Vastus lateralis electromyogram (EMG) was measured concomitantly. Significant sex, age and exercise effects (P less than 0.001) were observed for peak torque of both muscle groups. The effect of age on extensor strength was more pronounced at high speeds where men were also able to generate larger relative torques than women. No age or sex effects were noted for muscle endurance. However, muscles of active individuals demonstrated a greater resistance to fatigue than those of sedentary individuals. In conclusion, men were found to be stronger than women, age was associated with a decrease in muscle strength, but not of muscle endurance, and tennis players were stronger and had muscles that were more resistant to fatigue than their sedentary pairs in both age groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of training, exercise and diet on muscle glycolysis and liver gluconeogenesis.

Trained and untrained rats were fed either a control, high-fat, or high-carbohydrate diet and then sacrificed in either a rested or exhausted state. The $\text{in vitro}$ activity of several muscle glycolytic and liver gluconeogenic enzymes was measured. Muscle hexokinase, phosphorylase, and phosphofructokinase activities were increased after training. Hexokinase was decreased in exhausted rats. Phosphorylase and phosphofructokinase were increased in untrained-exhausted rats but were unchanged in trained-exhausted rats. Liver pyruvate carboxylase and phosphoenolpyruvate carboxykinase activities were increased in trained-rested rats fed a high-fat diet. In trained-exhausted rats phosphoenolpyruvate carboxykinase activity was increased regardless of diet fed. Blood glucose was decreased in trained-exhausted rats, but it was increased in untrained-exhausted rats. Plasma glucocorticoid level was increased in exhausted rats. This study showed that training was associated with an increased muscle glycolytic capacity. Training was also related to the ability of liver to increase phosphoenolpyruvate carboxykinase activity during exercise, thereby increasing gluconeogenic capacity.     

MR measurements of muscle damage and adaptation after eccentric exercise.

The purposes of this study were, first, to clarify the long-term pattern of T2 relaxation times and muscle volume changes in human skeletal muscle after intense eccentric exercise and, second, to determine whether the T2 response exhibits an adaptation to repeated bouts. Six young adult men performed two bouts of eccentric biceps curls (5 sets of 10 at 110% of the 1-repetition concentric maximum) separated by 8 wk. Blood samples, soreness ratings, and T2-weighted axial fast spin-echo magnetic resonance images of the upper arm were obtained immediately before and after each bout; at 1, 2, 4, 7, 14, 21, and 56 days after bout 1; and at 2, 4, 7 and 14 days after bout 2. Resting muscle T2 [27.6 +/- 0.2 (SE) ms] increased immediately postexercise by 8 +/- 1 ms after both bouts. T2 peaked 7 days after bout 1 at 47 +/- 4 ms and remained elevated by 2.5 ms at 56 days. T2 peaked lower (37 +/- 4 ms) and earlier (2-4 days) after bout 2, suggesting an adaptation of the T2 response. Peak serum creatine kinase values, pain ratings, and flexor muscle swelling were also significantly lower after the second bout (P < 0.05). Total volume of the imaged arm region increased transiently after bout 1 but returned to preexercise values within 2 wk. The exercised flexor compartment swelled by over 40%, but after 2 wk it reverted to a volume 10% smaller than that before exercise and maintained this volume loss through 8 wk, consistent with partial or total destruction of a small subpopulation of muscle fibers.     

Effects of exercise training and ACE inhibition on insulin action in rat skeletal muscle.

Our laboratory has demonstrated (Steen MS, Foianini KR, Youngblood EB, Kinnick TR, Jacob S, and Henriksen EJ, J Appl Physiol 86: 2044-2051, 1999) that exercise training and treatment with the angiotensin-converting enzyme (ACE) inhibitor trandolapril interact to improve insulin action in insulin-resistant obese Zucker rats. The present study was undertaken to determine whether a similar interactive effect of these interventions is manifest in an animal model of normal insulin sensitivity. Lean Zucker (Fa/-) rats were assigned to either a sedentary, trandolapril-treated (1 mg. kg(-1). day(-1) for 6 wk), exercise-trained (treadmill running for 6 wk), or combined trandolapril-treated and exercise-trained group. Exercise training alone or in combination with trandolapril significantly (P < 0.05) increased peak oxygen consumption by 26-32%. Compared with sedentary controls, exercise training alone or in combination with ACE inhibitor caused smaller areas under the curve for glucose (27-37%) and insulin (41-44%) responses during an oral glucose tolerance test. Exercise training alone or in combination with trandolapril also improved insulin-stimulated glucose transport in isolated epitrochlearis (33-50%) and soleus (58-66%) muscles. The increases due to exercise training alone or in combination with trandolapril were associated with enhanced muscle GLUT-4 protein levels and total hexokinase activities. However, there was no interactive effect of exercise training and ACE inhibition observed on insulin action. These results indicate that, in rats with normal insulin sensitivity, exercise training improves oral glucose tolerance and insulin-stimulated muscle glucose transport, whereas ACE inhibition has no effect. Moreover, the beneficial interactive effects of exercise training and ACE inhibition on these parameters are not apparent in lean Zucker rats and, therefore, are restricted to conditions of insulin resistance.     

Effect of exercise training on insulin binding and glucose metabolism in mouse soleus muscle

Training stimulates glucose uptake and metabolism by muscles independent of a rise in serum glucose. Whether this increased insulin action is associated with enhanced insulin binding in muscles is unknown. We studied the effect of 6 weeks of treadmill running on insulin binding, uptake of 2-deoxy-D-glucose, glycolysis, and glycogenesis by the soleus muscle of Swiss Webster mice. Training was progressively increased. The in vitro studies using intact soleus preparations were done 48 h after the last exercise bout. Training increased insulin binding, insulin-stimulated uptake of 2-deoxy-D-glucose, and glycogenesis but not glycolysis in the soleus. Our data suggest that the enhanced glucose uptake and metabolism in muscles induced by exercise training are associated with an increase in insulin binding.