Electrically elicited fatigue test of the quadriceps femoris muscle. Description and reliability

The purposes of this study were to develop an electrically elicited fatigue test (EEFT) that uses electrically elicited isometric muscle contractions and to examine the reliability of this test on a group of healthy individuals. Fifteen subjects were tested on two occasions, one week apart. The subjects were seated and the left leg secured to an isokinetic dynamometer with the knee positioned at 45 degrees of flexion. Maximum voluntary isometric contraction (MVIC) of the quadriceps femoris muscle was obtained and resultant knee extension torque was recorded. The quadriceps femoris muscle then was stimulated 50 times at the current level that elicited a knee extension torque level equal to 60% of that obtained during the MVIC. Percentages of decline in torque were calculated. Test-retest reliability indexes were calculated for the means of contractions 21 to 25 (r = .82, ICC = .83) and for contractions 46 to 50 (r = .92, ICC = .82). The EEFT was found to be reliable and may provide a clinically applicable means of measuring peripheral muscle fatigue.

Hamstring muscle strain treated by mobilizing the sacroiliac joint

The purpose of this study was to compare the effectiveness of two types of treatment of hamstring muscle strains. Twenty patients with hamstring muscle strains were assigned randomly to an Experimental Group (n = 10) or a Control Group (n = 10). Peak torque production of the quadriceps femoris and hamstring muscles and hamstring muscle length were measured before and after treatment. The hamstring muscles of the Experimental and Control groups were treated with moist heat followed by passive stretching. The Experimental Group also received manipulation of the sacroiliac joint. The change in hamstring muscle peak torque was significantly greater for the Experimental Group than for the Control Group (p less than .005). No significant differences existed between the two groups in either quadriceps femoris muscle peak torque or hamstring muscle length. The results of this study suggest a relationship between sacroiliac joint dysfunction and hamstring muscle strain.

Time course of loss of adaptations after stopping prolonged intense endurance training

Seven endurance exercise-trained subjects were studied 12, 21, 56, and 84 days after cessation of training. Maximal O2 uptake (VO2 max) declined 7% (P less than 0.05) during the first 21 days of inactivity and stabilized after 56 days at a level 16% (P less than 0.05) below the initial trained value. After 84 days of detraining the experimental subjects still had a higher VO2 max than did eight sedentary control subjects who had never trained (50.8 vs. 43.3 ml X kg-1 X min-1), due primarily to a larger arterial-mixed venous O2 (a-vO2) difference. Stroke volume (SV) during exercise was high initially and declined during the early detraining period to a level not different from control. Skeletal muscle capillarization did not decline with inactivity and remained 50% above (P less than 0.05) sedentary control. Citrate synthase and succinate dehydrogenase activities in muscle declined with a half-time of 12 days and stabilized at levels 50% above sedentary control (P less than 0.05). The initial decline in VO2 max was related to a reduced SV and the later decline to a reduced a-vO2 difference. Muscle capillarization and oxidative enzyme activity remained above sedentary levels and this may help explain why a-vO2 difference and VO2 max after 84 days of detraining were still higher than in untrained subjects.

Effect of weight training on blood pressure and hemodynamics in hypertensive adolescents

Six adolescents with persistent essential hypertension were examined to determine the effect of weight training on their blood pressure and hemodynamics. Five had first completed an endurance training program; one subject trained only by weight lifting. All subjects were reevaluated after 5 +/- 2 months of weight training, and 12 +/- 2 months after cessation of training. Endurance training resulted in an increase in VO2max and decreases in systolic and diastolic blood pressure. After weight training, VO2max had decreased to the level found prior to endurance training, and body weight was significantly increased. Systolic blood pressure after weight training was 17 +/- 4 mm Hg lower than when measured initially (P less than 0.01). Weight training maintained the reduction in diastolic pressure elicited by endurance exercise in those who initially had diastolic hypertension. Cessation of all forms of training resulted in no change in body weight, body fat, or VO2max from the values measured after weight training. Systolic pressure increased significantly with the cessation of training to a value not different from that measured initially. Diastolic pressure also increased after cessation of training, but was still below the initial value. The only significant hemodynamic change found was a reduction in systemic vascular resistance in response to weight training. Weight training in hypertensive adolescents appears to maintain the reductions in blood pressure achieved by endurance training, and may even elicit further reductions in blood pressure.

Effect of damp on isokinetic measurements

Meaningful use of isokinetic data requires understanding potential sources of variation and error. The purpose of this study was to examine one possible source of variation: the effect of recorder damp settings on Cybex II torque tracings. The effect of damp settings 0 through 4 at speeds of 30 degrees/sec and 75 degrees/sec was assessed by dropping loads of 13.65 kg and 36.85 kg attached to a lever arm of 30.5 cm on a Cybex II. The effect of damp settings at 180 degrees/sec was examined with the same weights at damp settings 2 and 4. Increasing damp resulted in 1) a decrease in amplitude of the entire torque curve and a decreased measurement of peak torque and 2) a shift of the torque curve to the right (later in time). The data underscore the need to record and to report the damp settings used during isokinetic testing.

Failure of endurance training to alter the cardiovascular response to static contraction

The purpose of this study was to determine whether endurance training alters the cardiovascular response to static contractions of the trained, but not untrained, musculature. Six healthy, untrained males (aged 23-36 years) underwent 10-12 weeks of intensive training involving both cycling and running. Peak VO2 on the bicycle ergometer, VO2max during graded treadmill running and concentrations of citrate synthase (CS) and malate dehydrogenase (MDH) in the vastus lateralis muscle were measured before and after training. Subjects performed static leg extension and forearm extension at 30% of maximal voluntary contraction until exhaustion before and after training. Heart rate (HR), systolic (SBP) and diastolic (DBP) blood pressure were measured at rest, and in addition to perceived exertion (PE), every 30 s during contraction. Endurance training elicited significant increases in peak VO2 (36%), VO2max (32%), CS (25%) and MDH (42%) (all P less than 0.05). HR at rest was significantly lower (P less than 0.05) after training, while SBP and DBP were unchanged. HR, SBP, DBP and PE increased throughout both types of static contractions. However, the magnitude of the increases were unaffected by training. In contrast to recent findings, these results suggest that the increases in heart rate and blood pressure in response to static contraction are not altered after endurance training in either the trained or the untrained muscle groups.

Electromyographic, peak torque, and power relationships during isokinetic movement

The use of isokinetic measurements for research and clinical practice becomes more meaningful when it can be demonstrated that subjects being tested at multiple velocities are making similar efforts and when the relationships between various biomechanical measures are understood. The purpose of this study was to examine 1) integrated electromyographic activity per second of the quadriceps femoris muscle at four isokinetic speeds (30, 60, 90, and 120 degrees/sec) and 2) the relationship of power to peak torque at each speed. Two groups were tested: "normals" (healthy subjects) and patients undergoing long-term steroid therapy for rheumatic diseases. The integrated electromyographic activity per second did not vary significantly across speeds, indicating that subjects in each group made equivalent efforts at all four speeds. At each speed, for each group, high correlations were found between peak torque and power. Population-specific and speed-specific linear regression equations were calculated that allowed for predictions of power from the more easily obtained clinical measure of peak torque.

Muscle function in rheumatic disease patients treated with corticosteroids

Clinical and experimental data indicate that long-term corticosteroid use leads to atrophy of the type 2 muscle fibers. The purpose of this study was to characterize and quantify the nature of muscle function in rheumatic disease patients who have been on long-term corticosteroid therapy. Quadriceps function (i.e., peak torque and power) in 19 patients (11 with rheumatoid arthritis, five with systemic lupus erythematosis, and 3 other) and 11 age- and activity-matched normal controls was measured with an isokinetic dynamometer (Cybex II), during four constant velocity movements. Power was significantly lower for the patients at all speeds. At the higher speeds the patients' deficit in power production increased as indicated by a difference in the slopes of power-velocity regression lines. Measures of peak torque could not be consistently used to differentiate the groups. Patients with rheumatic diseases receiving corticosteroids have a decreased ability to generate muscle power. The method described allows for quantification of these deficits in a clinical setting.

Blood lactate threshold in some well-trained ischemic heart disease patients

Six patients with ischemic heart disease who had exercised intensely for longer than 1 yr appeared to have a disproportionately high capacity for endurance exercise relative to VO2 max. They were compared with healthy runners of the same age (mean 55 yr) with similar training programs (6-12 km/day, 5 day/wk). The trained patients had a significantly (P less than 0.05) lower maximal cardiac output (-17%) and VO2 max (-18%, 37 vs. 45 ml . kg-1 . min-1). Despite their lower VO2 max, the trained patients were able to run 8 km at the same speed as the normal runners (approximately 189 m/min). The trained patients' ability to keep pace with the normal subjects was apparently due to a very high lactate threshold (LT) relative to VO2 max. The patients' LT (lactate 1 mM above base line) occurred at a treadmill running speed of 176 m/min, which elicited 100% of their VO2 max, compared with a LT at 178 m/min and 84% of VO2 max in the normal subjects (P less than 0.01). Our results show that some individuals with VO2 max limited by impaired cardiac function can undergo adaptations to training that enable them to maintain close to a metabolic steady state during exercise that elicits VO2 max.