Transfer effects in endurance exercise. Adaptations in trained and untrained muscles

The effects of 8 weeks of bicycle endurance training (5 X /week for 30 min) on maximal oxygen uptake capacity (VO2max) during arm and leg ergometry, and on the ultrastructure of an untrained arm muscle (m. deltoideus), and a trained leg muscle (m. vastus lateralis) were studied. With the training, leg-VO2max for bicycling increased by +13%, while the capillary per fiber ratio and the volume density of mitochondria in m. vastus lateralis increased by +15% and +40%, respectively. In contrast, the untrained m. deltoideus showed an unchanged capillary per fiber ratio and a decreased mitochondrial volume density (-17%). Despite this decrease of mitochondrial volume arm-VO2max increased by +9%. It seems unlikely that the observed discrepancy can be explained by cardiovascular adaptations, since arm cranking did not fully tax the cardiovascular system (arm-VO2max/leg-VO2max: 0.74 and 0.71 before and after training, respectively). Thus neither cardiovascular adaptations nor local structural changes in the untrained muscles could explain the increased arm-VO2max. However, the enhanced capacity for lactate clearance after endurance training could be sufficient to account for the larger VO2max during arm cranking. We propose that an increased net oxidation of lactate might be responsible for the increased arm-VO2max found after bicycle endurance training.     

Determinants of endurance in well-trained cyclists

Fourteen competitive cyclists who possessed a similar maximum O2 consumption (VO2 max; range, 4.6-5.0 l/min) were compared regarding blood lactate responses, glycogen usage, and endurance during submaximal exercise. Seven subjects reached their blood lactate threshold (LT) during exercise of a relatively low intensity (group L) (i.e., 65.8 +/- 1.7% VO2 max), whereas exercise of a relatively high intensity was required to elicit LT in the other seven men (group H) (i.e., 81.5 +/- 1.8% VO2 max; P less than 0.001). Time to fatigue during exercise at 88% of VO2 max was more than twofold longer in group H compared with group L (60.8 +/- 3.1 vs. 29.1 +/- 5.0 min; P less than 0.001). Over 92% of the variance in performance was related to the % VO2 max at LT and muscle capillary density. The vastus lateralis muscle of group L was stressed more than that of group H during submaximal cycling (i.e., 79% VO2 max), as reflected by more than a twofold greater (P less than 0.001) rate of glycogen utilization and blood lactate concentration. The quality of the vastus lateralis in groups H and L was similar regarding mitochondrial enzyme activity, whereas group H possessed a greater percentage of type I muscle fibers (66.7 +/- 5.2 vs. 46.9 +/- 3.8; P less than 0.01). The differing metabolic responses to submaximal exercise observed between the two groups appeared to be specific to the leg extension phase of cycling, since the blood lactate responses of the two groups were comparable during uphill running. These data indicate that endurance can vary greatly among individuals with an equal VO2 max.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of contractile activity on rat skeletal muscle beta-adrenoceptor properties

The effect of fiber type and endurance exercise training on skeletal muscle beta-adrenoceptor properties were assessed using a direct radioligand binding technique. Six separate muscles, composed of a variety of different fiber types, were examined in treadmill trained and sedentary rats. In trained animals, sarcolemmal preparations from heart and slow twitch soleus muscle exhibited a significantly greater receptor concentration than membranes from white fast twitch glycolytic fibers of the vastus lateralis. No significant changes were observed between trained and sedentary rat muscle beta-adrenoceptor density (beta max, fmole/mg protein) or affinity (Kd, nM) within each muscle type, despite significantly increased myocardial/body weight ratios and skeletal muscle enzyme adaptations associated with the exercise program. These results suggest that muscle beta-adrenoceptor properties may be influenced in part by the motor nerve innervation to that muscle, and are further discussed with respect to a possible relationship between exercise intensity and receptor regulation.     

EMG versus oxygen uptake during cycling exercise in trained and untrained subjects.

The aim of this study was to test the hypothesis that bicycle training may improve the relationship between the global SEMG energy and VO2. We already showed close adjustment of the root mean square (RMS) of the surface electromyogram (SEMG) to the oxygen uptake (VO2) during cycling exercise in untrained subjects. Because in these circumstances an altered neuromuscular transmission which could affect SEMG measurement occurred in untrained individuals only, we searched for differences in the SEMG vs. VO2 relationship between untrained subjects and well-trained cyclists. Each subject first performed an incremental exercise to determine VO2max and the ventilatory threshold, and second a constant-load threshold cycling exercise, continued until exhaustion. SEMG from both vastus lateralis muscles was continuously recorded. RMS was computed. M-Wave was periodically recorded. During incremental exercise: (1) a significant non-linear positive correlation was found between RMS increase and VO2 increase in untrained subjects, whereas the relationship was best fitted by a straight line in trained cyclists; (2) the RMS/VO2 ratio decreased progressively throughout the incremental exercise, its decline being significantly and markedly accentuated in trained cyclists; (3) in untrained subjects, significant M-wave alterations occurred at the end of the trial. These M-wave alterations could explain the non-linear RMS increase in these individuals. During constant-load exercise: (1) after an initial increase, the VO2 ratio decreased progressively to reach a plateau after 2 min of exercise, but no significant inter-group differences were noted; (2) no M-wave changes were measured in the two groups. We concluded that the global SEMG energy recorded from the vastus lateralis muscle is a good estimate of metabolic energy expenditure during incremental cycling exercise only in well-trained cyclists.     

Human skeletal muscle fiber type alteration with high-intensity intermittent training

The response of muscle fiber type proportions and fiber areas to 15 weeks of strenuous high-intensity intermittent training was investigated in twenty-four carefully ascertained sedentary (14 women and 10 men) and 10 control (4 women and 6 men) subjects. The supervised training program consisted mainly of series of supramaximal exercise lasting 15 s to 90 s on a cycle ergometer. Proportions of muscle fiber type and areas of the fibers were determined from a biopsy of the vastus lateralis before and after the training program. No significant change was observed for any of the histochemical characteristics in the control group. Training significantly increased the proportion of type I and decreased type IIb fibers, the proportion of type IIa remained unchanged. Areas of type I and IIb fibers increased significantly with training. These results suggest that high-intensity intermittent training in humans may alter the proportion of type I and the area of type I and IIb fibers and in consequence that fiber type composition in human vastus lateralis muscle is not determined solely by genetic factors.     

Effects of strength, endurance, and concurrent training on aerobic power and dynamic neuromuscular economy in elderly men

The aim of this study was to investigate the effects of concurrent training on endurance capacity and dynamic neuromuscular economy in elderly men. Twenty-three healthy men (65 ± 4 years) were divided into 3 groups: concurrent (CG, n = 8), strength (SG, n = 8), and aerobic training group (EG, n = 7). Each group trained 3 times a week for 12 weeks, strength training, aerobic training, or both types of training in the same session. The maximum aerobic workload (Wmax) and peak oxygen uptake (VO2peak) of the subjects were evaluated on a cycle ergometer before and after the training period. Moreover, during the maximal test, muscle activation was measured at each intensity by means of electromyographic signals from the vastus lateralis (VL), rectus femoris (RF), biceps femoris long head, and gastrocnemius lateralis to determine the dynamic neuromuscular economy. After training, significant increases in VO2peak and Wmax were only found in the CG and EG (p < 0.05), with no difference between groups. Moreover, there was a significant decrease in myoelectric activity of the RF muscle at 50 (EG), 75 and 100 W (EG and CG) and in the VL for the 3 groups at 100 W (p < 0.05). No change was seen in the electrical signal from the lateral gastrocnemius muscle and biceps femoris. The results suggest specificity in adaptations investigated in elderly subjects, because the most marked changes in the neuromuscular economy occurred in the aerobically trained groups.     

Relationships between muscle mitochondrial DNA content, mitochondrial enzyme activity and oxidative capacity in man: alterations with disease

Muscle mitochondrial content is tightly regulated, and requires the expression of both nuclear and mitochondrial genes. In addition, muscle mitochondrial content is a major determinant of aerobic exercise capacity in healthy subjects. The current study was designed to test the hypothesis that in healthy humans, muscle mitochondrial DNA (mtDNA) content is correlated with citrate synthase activity (a representative nuclear-encoded mitochondrial enzyme) and aerobic exercise capacity as defined by whole-body peak oxygen consumption (VO2). Furthermore, it was postulated that these relationships might be altered with disease. Twelve healthy and five paraplegic subjects underwent exercise testing and vastus lateralis muscle biopsy sampling. An additional ten healthy subjects and eight patients with unilateral peripheral arterial disease (PAD) underwent exercise testing and gastrocnemius muscle biopsy sampling. Citrate synthase activity and mtDNA content were positively correlated in the vastus lateralis muscles from the healthy subjects. This relationship was similar in muscle from paraplegic subjects. mtDNA content was positively correlated with peak VO2 in the healthy subjects and in the paraplegic subjects in whom peak VO2 had been elicited by functional electrical stimulation of the muscle. In contrast, the PAD subjects demonstrated higher mtDNA contents than would have been predicted based on their claudication-limited peak VO2. Thus, in healthy humans there are strong relationships between muscle mtDNA content and both muscle citrate synthase activity and peak VO2. These relationships are consistent with coordinant nuclear DNA and mtDNA expression, and with mitochondrial content being a determinant of aerobic exercise capacity. The relationships seen in healthy humans are quantitatively similar in paraplegic patients, but not in patients with PAD, a disease which is associated with a metabolic myopathy. The relationships between mtDNA content, mitochondrial enzyme activities and exercise capacity provide insight into the physiologic and pathophysiologic regulation of muscle mitochondrial expression.     

Muscle and blood redox status after exercise training in severe COPD patients

Beneficial effects of exercise training in patients with chronic obstructive pulmonary disease (COPD) are acknowledged. However, high-intensity exercise may enhance muscle oxidative stress in severe COPD patients. We hypothesized that high-intensity exercise training of long duration does not deteriorate muscle redox status. In the vastus lateralis and blood of 18 severe COPD patients and 12 controls, before and after an 8-week training program, protein oxidation and nitration, antioxidant systems, and inflammatory cytokines were examined. At baseline, COPD patients showed greater muscle oxidative stress and superoxide dismutase activity and circulating inflammatory cytokines than controls. Among COPD patients, muscle and blood protein carbonylation levels were correlated. Both groups showed training-induced increase in VO(2) peak and decreased blood lactate levels. After training, among the COPD patients, blood protein nitration levels were significantly reduced and muscle protein oxidation and nitration levels did not cause impairment. Muscle and blood levels of inflammatory cytokines were not modified by training in either patients or controls. We conclude that in severe COPD patients, high-intensity exercise training of long duration improves exercise capacity while preventing the enhancement of systemic and muscle oxidative stress. In addition, in these patients, resting protein oxidation levels correlate between skeletal muscle and blood compartments.     

Muscle hypertrophy response to resistance training in older women.

We conducted a 12-wk resistance training program in elderly women [mean age 69 +/- 1.0 (SE) yr] to determine whether increases in muscle strength are associated with changes in cross-sectional fiber area of the vastus lateralis muscle. Twenty-seven healthy women were randomly assigned to either a control or exercise group. The program was satisfactorily completed and adequate biopsy material obtained from 6 controls and 13 exercisers. After initial testing of baseline maximal strength, exercisers began a training regimen consisting of seven exercises that stressed primary muscle groups of the lower extremities. No active intervention was prescribed for the controls. Increases in muscle strength of the exercising subjects were significant compared with baseline values (28-115%) in all muscle groups. No significant strength changes were observed in the controls. Cross-sectional area of type II muscle fibers significantly increased in the exercisers (20.1 +/- 6.8%, P = 0.02) compared with baseline. In contrast, no significant change in type II fiber area was observed in the controls. No significant changes in type I fiber area were found in either group. We conclude that a program of resistance exercise can be safely carried out by elderly women, such a program significantly increases muscle strength, and such gains are due, at least in part, to muscle hypertrophy.     

Effect of training and detraining on skeletal muscle glucose transporter (GLUT4) content in rats.

The aim of the present study was to examine the effects of treadmill exercise training and detraining on the skeletal muscle fiber type specific expression of the insulin-regulated glucose transporter protein (GLUT4) in rats. GLUT4 protein content was determined by Western and dot-blot analysis, using a polyclonal antibody raised against the carboxy-terminal peptide. Rats were sacrificed 24 h after the last training session. There were no significant changes in muscle GLUT4 after 1 day or 1 week of training. Six weeks of training increased GLUT4 protein content 1.4- to 1.7-fold (p < 0.05) over controls in the soleus and red vastus lateralis, whereas no significant change was evident in the white vastus lateralis muscle. GLUT4 protein content in both soleus and red vastus lateralis muscle returned to near control values after 7 days of detraining. Similar to GLUT4, citrate synthase activity showed no change after 1 day or 1 week of training, increased 1.8-fold over controls after 6 weeks of training, but returned to control values after 7 days detraining. These findings demonstrate that muscle GLUT4 protein is increased in rats with as little as 6 weeks of treadmill exercise training but that the adaptation is lost within 1 week of detraining. It is suggested that expression of the GLUT4 protein is coordinated with the well-documented adaptations in oxidative enzyme activity with endurance training and detraining.     

Early muscular and metabolic adaptations to prolonged exercise training in humans

A short-term training program involving 2 h of daily exercise at 59% of peak O2 uptake (VO2max) repeated for 10-12 consecutive days was employed to determine the significance of adaptations in energy metabolic potential on alterations in energy metabolism and substrate utilization in working muscle. The initial VO2max determined before training on the eight male subjects was 53.0 +/- 2.0 (SE) ml.kg-1.min-1. Analysis of samples obtained by needle biopsy from the vastus lateralis muscle before exercise (0 min) and at 15, 60, and 99 min of exercise indicated that on the average training resulted (P less than 0.05) in a 6.5% higher concentration of creatine phosphate, a 9.9% lower concentration of creatine, and a 39% lower concentration of lactate. Training had no effect on ATP concentration. These adaptations were also accompanied by a reduction in the utilization in glycogen such that by the end of exercise glycogen concentration was 47.1% higher in the trained muscle. Analysis of the maximal activities of representative enzymes of different metabolic pathways and segments indicated no change in potential in the citric acid cycle (succinate dehydrogenase, citrate synthase), beta-oxidation (3-hydroxyacyl CoA dehydrogenase), glucose phosphorylation (hexokinase), or potential for glycogenolysis (phosphorylase) and glycolysis (pyruvate kinase, phosphofructokinase, alpha-glycerophosphate dehydrogenase, lactate dehydrogenase). With the exception of increases in the capillary-to-fiber area ratio in type IIa fibers, no change was found in any fiber type (types I, IIa, and IIb) for area, number of capillaries, capillary-to-fiber area ratio, or oxidative potential with training.(ABSTRACT TRUNCATED AT 250 WORDS)     

Skeletal muscle oxygenation during incremental exercise

The purpose of this study was to investigate the relationship between muscle oxygenation level at exhaustion and maximal oxygen uptake (VO2max) in an incremental cycling exercise. Nine male subjects took part in an incremental exhaustive cycling exercise, and then cuff occlusion was performed. Changes in oxy-(deltaHbO2) and deoxy-(deltaHb) hemoglobin concentrations in the vastus lateralis muscle were measured with a near infrared spectroscopy (NIRS). Muscle oxygenation during incremental exercise was expressed as a percentage (%Moxy) of the maximal range observed during an arterial occlusion as the lower reference point. A systematic decrease was observed in %Moxy with increasing intensity. A significant relationship was observed between %Moxy at exhaustion and VO2max (p < 0.01). We concluded that the one of the limiting factor of VO2max is the muscle oxygen diffusion capacity, and %Moxy during exercise could be one of the indexes of muscle oxygen diffusion capacity.     

Influence of priming exercise on pulmonary O2 uptake kinetics during transitions to high-intensity exercise from an elevated baseline.

It has been suggested that the slower O2 uptake (VO2) kinetics observed when exercise is initiated from an elevated baseline metabolic rate are linked to an impairment of muscle O2 delivery. We hypothesized that "priming" exercise would significantly reduce the phase II time constant (tau) during subsequent severe-intensity cycle exercise initiated from an elevated baseline metabolic rate. Seven healthy men completed exercise transitions to 70% of the difference between gas exchange threshold (GET) and peak VO2 from a moderate-intensity baseline (90% GET) on three occasions in each of the "unprimed" and "primed" conditions. Pulmonary gas exchange, heart rate, and the electromyogram of m. vastus lateralis were measured during all tests. The phase II VO2 kinetics were slower when severe exercise was initiated from a baseline of moderate exercise compared with unloaded pedaling (mean+/-SD tau, 42+/-15 vs. 33+/-8 s; P<0.05), but were not accelerated by priming exercise (42+/-17 s; P>0.05). The amplitude of the VO2 slow component and the change in electromyogram from minutes 2 to 6 were both significantly reduced following priming exercise (VO2 slow component: from 0.47+/-0.09 to 0.27+/-0.13 l/min; change in integrated electromyogram between 2 and 6 min: from 51+/-35 to 26+/-43% of baseline; P<0.05 for both comparisons). These results indicate that the slower phase II VO2 kinetics observed during transitions to severe exercise from an elevated baseline are not altered by priming exercise, but that the reduced VO2 slow component may be linked to changes in muscle fiber activation.     

Relationship between muscle fatigue and oxygen uptake during cycle ergometer exercise with different ramp slope increments.

The surface electromyogram (EMG) from active muscle and oxygen uptake (VO2) were studied simultaneously to examine changes of motor unit (MU) activity during exercise tests with different ramp increments. Six male subjects performed four exhausting cycle exercises with different ramp slopes of 10, 20, 30 and 40 W.min-1 on different days. The EMG signals taken from the vastus lateralis muscle were stored on a digital data recorder and converted to obtain the integrated EMG (iEMG). The VO2 was measured, with 20-s intervals, by the mixing chamber method. A non-linear increase in iEMG against work load was observed for each exercise in all subjects. The break point of the linear relationship of iEMG was determined by the crossing point of the two regression lines (iEMGbp). Significant differences were obtained in the exercise intensities corresponding to maximal oxygen uptake (VO2max) and the iEMGbp between 10 and 30, and 10 and 40 W.min-1 ramp exercises (P < 0.05). However, no significant differences were obtained in VO2max and VO2 corresponding to the iEMGbp during the four ramp exercises. With respect to the relationship between VO2 and exercise intensity during the ramp increments, the VO2-exercise intensity slope showed significant differences only for the upper half (i.e. above iEMGbp). These results demonstrated that the VO2max and VO2 at which a nonlinear increase in iEMG was observed were not varied by the change of ramp slopes but by the exercise intensity corresponding to VO2max and the iEMGbp was varied by the change of ramp slopes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Exercise training increases branched-chain oxoacid dehydrogenase kinase content in human skeletal muscle

The branched-chain oxoacid dehydrogenase complex (BCOAD) is rate determining for the oxidation of branched-chain amino acids (BCAAs) in skeletal muscle. Exercise training blunts the acute exercise-induced activation of BCOAD (BCOADa) in human skeletal muscle (McKenzie S, Phillips SM, Carter SL, Lowther S, Gibala MJ, Tarnopolsky MA. Am J Physiol Endocrinol Metab 278: E580-E587, 2000); however, the mechanism is unknown. We hypothesized that training would increase the muscle protein content of BCOAD kinase, the enzyme responsible for inactivation of BCOAD by phosphorylation. Twenty subjects [23 +/- 1 yr; peak oxygen uptake (.VO(2peak)) = 41 +/- 2 ml.kg(-1).min(-1)] performed 6 wk of either high-intensity interval or continuous moderate-intensity training on a cycle ergometer (n = 10/group). Before and after training, subjects performed 60 min of cycling at 65% of pretraining .VO(2peak), and needle biopsy samples (vastus lateralis) were obtained before and immediately after exercise. The effect of training was demonstrated by an increased .VO(2peak), increased citrate synthase maximal activity, and reduced muscle glycogenolysis during exercise, with no difference between groups (main effects, P < 0.05). BCOADa was lower after training (main effect, P < 0.05), and this was associated with a approximately 30% increase in BCOAD kinase protein content (main effect, P < 0.05). We conclude that the increased protein content of BCOAD kinase may be involved in the mechanism for reduced BCOADa after exercise training in human skeletal muscle. These data also highlight differences in models used to study the regulation of skeletal muscle BCAA metabolism, since exercise training was previously reported to increase BCOADa during exercise and decrease BCOAD kinase content in rats (Fujii H, Shimomura Y, Murakami T, Nakai N, Sato T, Suzuki M, Harris RA. Biochem Mol Biol Int 44: 1211-1216, 1998).     

Effects of endurance training on a mitochondrial reticulum in limb skeletal muscle

High voltage electron microscopy at 1500 kV, was used to examine the effects of endurance training on mitochondrial morphology in rat skeletal muscle. The soleus, deep portions of the vastus lateralis, and superficial portions of the vastus lateralis muscles were examined to represent slow-twitch-oxidative, fast-twitch-oxidative-glycolytic, and fast-twitch-glycolytic skeletal muscle fiber types, respectively. Muscle samples were removed from endurance trained and untrained control female Wistar rats (n = 6, each group). Tissues were fixed using standard electron microscopic techniques and sectioned transversely with respect to muscle fiber orientation to approximately, 0.5 micron thickness. The sections were stained on grids with uranyl acetate and Reynolds' lead citrate. Results confirmed the presence of a mitochondrial reticulum in all three skeletal muscle fiber types of both groups. Stereologic analyses indicated volume densities of intermyofibrillar mitochondria increased significantly (P less than 0.05) with endurance training in the three skeletal muscle fiber types. Surface-to-volume ratio of mitochondria was significantly decreased (P less than 0.05) after training only in the deep portion of the vastus lateralis muscle. It was concluded that the mitochondria in mammalian limb skeletal muscle are a reticulum which adapts to endurance training by proliferating.     

Functional properties of human muscle fibers after short-term resistance exercise training

The aim of this study was to assess the relationships between human muscle fiber hypertrophy, protein isoform content, and maximal Ca(2+)-activated contractile function following a short-term period of resistance exercise training. Six male subjects (age 27 +/- 2 yr) participated in a 12-wk progressive resistance exercise training program that increased voluntary lower limb extension strength by >60%. Single chemically skinned fibers were prepared from pre- and posttraining vastus lateralis muscle biopsies. Training increased the cross-sectional area (CSA) and peak Ca(2+)-activated force (P(o)) of fibers containing type I, IIa, or IIa/IIx myosin heavy chain by 30-40% without affecting fiber-specific force (P(o)/CSA) or unloaded shortening velocity (V(o)). Absolute fiber peak power rose as a result of the increase in P(o), whereas power normalized to fiber volume was unchanged. At the level of the cross bridge, the effects of short-term resistance training were quantitative (fiber hypertrophy and proportional increases in fiber P(o) and absolute power) rather than qualitative (no change in P(o)/CSA, V(o), or power/fiber volume).     

Effects of depletion exercise and light training on muscle glycogen supercompensation in men

Supercompensated muscle glycogen can be achieved by using several carbohydrate (CHO)-loading protocols. This study compared the effectiveness of two "modified" CHO-loading protocols. Additionally, we determined the effect of light cycle training on muscle glycogen. Subjects completed a depletion (D, n = 15) or nondepletion (ND, n = 10) CHO-loading protocol. After a 2-day adaptation period in a metabolic ward, the D group performed a 120-min cycle exercise at 65% peak oxygen uptake (VO2 peak) followed by 1-min sprints at 120% VO2 peak to exhaustion. The ND group performed only 20-min cycle exercise at 65% VO2 peak. For the next 6 days, both groups ate the same high-CHO diets and performed 20-min daily cycle exercise at 65% VO2 peak followed by a CHO beverage (105 g of CHO). Muscle glycogen concentrations of the vastus lateralis were measured daily with 13C magnetic resonance spectroscopy. On the morning of day 5, muscle glycogen concentrations had increased 1.45 (D) and 1.24 (ND) times baseline (P < 0.001) but did not differ significantly between groups. However, on day 7, muscle glycogen of the D group was significantly greater (p < 0.01) than that of the ND group (130 +/- 7 vs. 104 +/- 5 mmol/l). Daily cycle exercise decreased muscle glycogen by 10 +/- 2 (D) and 14 +/- 5 mmol/l (ND), but muscle glycogen was equal to or greater than preexercise values 24 h later. In conclusion, a CHO-loading protocol that begins with a glycogen-depleting exercise results in significantly greater muscle glycogen that persists longer than a CHO-loading protocol using only an exercise taper. Daily exercise at 65% VO2 peak for 20 min can be performed throughout the CHO-loading protocol without negatively affecting muscle glycogen supercompensation.     

Fiber type changes in rat skeletal muscle after intense interval training

Female Sprague-Dawley rats were subjected to a ten week training program to determine the influence of intense interval running on the fiber type composition of selected hindlimb muscles; soleus (S), plantaris (P), deep vastus lateralis (DVL), and superficial vastus lateralis (SVL). The muscles of one hindlimb were used for histochemical ATPase analysis to determine the distribution of fiber types and those of the contralateral hindlimb were assayed biochemically for citrate synthase activity (an aerobic marker). Training induced a significant increase in citrate synthase activity in each muscle section. The largest absolute increase occurred in the DVL and the largest relative increase occurred in the SVL. The distribution of fiber types within the S (85% slow-twitch) and SVL (100% fast-twitch) remained unchanged with training. However, significant increases in the percentage of type I (slow-twitch) fibers in both the P (2-fold) and DVL (3-fold) were observed with concomitant decreases in the type II (fast-twitch) population. In addition, training induced significant changes in the fast-twitch subtype populations of the DVL (IIB----IIA). These data suggest exercise-induced fiber type transformations occurring both within the fast-twitch population and between fast-twitch and slow-twitch fibers in certain hindlimb muscles of the rat following a high intensity interval training program.     

Biofeedback as a means to alter electromyographic activity in a total knee replacement patient

This paper presents a single case controlled study of a 75-year-old male having bilateral total knee replacement. Baseline EMG recordings demonstrated differential levels of vastus medialis and vastus lateralis muscle activity in both knees during exercise, with increased vastus lateralis activity compared to vastus medialis activity. The purpose of the study was to use electromyographic (EMG) biofeedback training to train the patient to equalize vastus medialis and vastus lateralis EMG activity during exercise. After 11 and 13 training sessions for the left and right knees, respectively, differences between vastus medialis and vastus lateralis activity had markedly decreased. Following the termination of biofeedback training, EMG activity during exercise showed a return toward baseline levels. Several concomitant changes in psychological and physical function were noted. These results suggested that EMG biofeedback can be used to train vastus medialis and vastus lateralis activity in total knee replacement patients, and that biofeedback training may produce positive benefits in other functional areas.