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Biomedical subjects

H E Berg

Publications and source records attributed to H E Berg.

10 recordsLinked to original sources
PubMed1996

Effects of removal of weight-bearing function on contractility and myosin isoform composition in single human skeletal muscle cells.

The purpose of this study was to investigate the effects of a 6-week period without weight bearing, achieved by bed rest, on the contractile behaviour, myosin isoform expression and myofibrillar protein content of single human muscle fibres. Percutaneous biopsied specimens of the quadriceps muscle were taken from three healthy male volunteers before and at the end of the experimental period. Maximum force normalised to cross-sectional area (specific tension), maximum velocity of unloaded shortening (V0), and myosin heavy chain (MyHC) and light chain (MyLC) isoform composition were measured in single membrane-permeabilised muscle cells obtained from these specimens. At the end of the experimental period, specific tension was reduced (P < 0.001) by 40% and there was a parallel decline in myofibrillar protein content per muscle cell volume. V0 did not change significantly in response to bed rest when data from all muscle cells were pooled. In two of the subjects, however, V0 decreased (P < 0.01-0.001) in muscle cells expressing the beta/slow (type I) MyHC isoform, but there was no change in fibres expressing type IIA or a combination of type IIA and IIB MyHCs. The slowing in type I MyHC fibres was associated with a change in the isoform composition of the regulatory MyLC.

Adult↗
PubMed1996

Changes in muscle function in response to 10 days of lower limb unloading in humans.

Force-generating capacity and electromyographic (EMG) activity of the knee extensor muscles were studied before and after short-term (10 d) unilateral lower limb unloading and during 4 days of recovery. Ten healthy males used crutches to prevent one of their lower limbs from weight-bearing while maintaining joint mobility as well as daily ambulatory activities. Knee extensor torque and quadriceps rectified EMG during maximal voluntary isometric contraction (MVC) was measured repeatedly before and after the intervention. Also, EMG at a fixed submaximal level (100 Nm; 30-45% MVC) and maximal angular velocity (AVmax), during unresisted knee extension, were assessed. Maximum torque decreased (P < 0.05) by 13 +/- 8% in response to unloading while maximum EMG activity did not change after unloading or during recovery (P = 0.35). Submaximum EMG increased (P < 0.05) by 25 +/- 16% after unloading. Maximum and submaximum torque/EMG ratio decreased (P < 0.05) after unloading. AVmax decreased (P < 0.05) by 9 +/- 8% after unloading. The post value, however, was not different from that of the weight-bearing limb. Torque, EMG and AVmax were recovered (P > 0.05) after 4 days of resumed weight-bearing. The pronounced decrease and the rapid recovery in maximum torque appears not to be attributed to a change in muscle mass alone. Because the findings of unchanged maximum EMG and increased EMG at a submaximal force level suggest no change in neural drive, we propose that unspecific tissue factors in part impair muscle function in response to short-term loss of weight-bearing activity. Results also indicate that recovery in muscle function after short-term unloading seems to be completed in a time span shorter than the period of preceding inactivity.

Adult↗
PubMed1995

Involvement of eccentric muscle actions in giant slalom racing.

Joint angular movements and muscle activation (EMG), were determined in male elite racers while performing the giant slalom. Movement cycles averaged 3.5 +/- 0.6 s (left plus right turn), and knee angle ranged 66-114 degrees (180 degrees = straight leg). Knee extensor muscle use was dominated (rectified EMG; P < 0.05) by the leg controlling the outside (downhill) ski during the turn. Time spent while decreasing knee angle (eccentric muscle action) of outside leg averaged 1.0 +/- 0.2 s. This phase was longer (P < 0.05) than the average push-off (concentric muscle action) phase of 0.5 +/- 0.1 s. Moreover, EMG activity of the outside leg during eccentric muscle actions exceeded (P < 0.05) that of concentric actions and was similar to that attained during maximum isometric knee extension in laboratory tests. Knee and hip angular movement ranged 20-50 degrees. Average joint velocities equalled 20-40 degrees.s(-1) during the turning phase. Thus, competitive giant slalom skiing is dominated by slow eccentric muscle actions performed at near maximum voluntary force. Because of their greater ability to generate force, eccentric muscle actions may be warranted or even required to resist the G-forces induced during the turn phase.

Adult↗
PubMed1994

Dynamic neck strength training effect on pain and function.

This study examined whether neck resistance training could increase strength and reduce pain in workers with a high prevalence of neck disorders. Middle-aged women workers (n = 17) exercised twice weekly for 8 weeks. Each session (12min) consisted of three sets of 12 repetitions of resisted rotation, flexion, and extension muscles using hydraulic dampers. Resistance was set individually and progressively increased every second week. Angle-specific maximal isometric rotator, extensor, and flexor torque was measured before and after training. Torque during rotation, flexion and extension increased (p < .05) on average 35%, 27%, and 19%, respectively, after training. Perceived pain, assessed using a four-graded scale, was reduced (p < .05) after training. It is suggested that 12 minutes of specific neck strength training twice weekly for 8 weeks increases strength of rotator, extensor, and flexor muscles of the neck. Also all individuals who had pain reported reduced perceived neck pain after training.

Adult↗
PubMed1994

A gravity-independent ergometer to be used for resistance training in space.

An ergometer, to be used for resistance training in space, has been developed and validated. It is designed to activate the extensor muscles of the knee and ankle joints while performing the leg press exercise. Resistance is provided independent of gravity by using the inertial focus of a flywheel. Eleven men performed two series of consecutive maximal voluntary concentric and eccentric muscle actions. Force, power, work and electromyographic (EMG) activity, measured during exercise on this ergometer and a traditional leg press resistive apparatus were similar. This mechanical ergometer seems to meet the operational and technical requirements of equipment that can be flown and used in space. Also, the physiological responses to acute exercise suggest that adaptations similar to those achieved by traditional weight training can be produced. Exercise using the inertia ergometer would, therefore, probably also be effective in combating the muscle atrophy and loss of strength that occur in microgravity.

Adult↗
PubMed1993

Work capacity and metabolic and morphologic characteristics of the human quadriceps muscle in response to unloading.

The response of skeletal muscle to unweighting was studied in six healthy males who were subjected to four weeks of lowerlimb suspension. They performed three bouts of 30 consecutive maximal concentric knee extensions, before unloading and the day after (POST 1), 4 days after (POST 2) and 7 weeks after (REC) resumed weight-bearing. Peak torque of each contraction was recorded and work was calculated as the mean of the average peak torque for the three bouts and fatigability was measured as the decline in average peak torque over bouts. Needle biopsies were obtained from m. vastus lateralis of each limb before and at POST 1. Muscle fibre type composition and area, capillarity and the enzyme activities of citrate synthase (CS) and phosphofructokinase (PFK) were subsequently analysed. Mean average peak torque for the three bouts at POST1, POST2 and REC was reduced (P < 0.05) by 17, 13 and 7%, respectively. Fatigability was greater (P < 0.05) at POST2 than before unloading. Type I, IIA and IIB percentage, Type I and II area and capillaries per fibre of Type I and II did not change (P > 0.05) in response to unloading. The activity of CS, but not PFK, decreased (P < 0.05) after unloading. The weight-bearing limb showed no changes in the variables measured. The results of this study suggest that this human lowerlimb suspension model produces substantial impairments of work and oxidative capacity of skeletal muscle. The performance decrements are most likely induced by lack of weight-bearing.

Adult↗
PubMed1993

Changes in lower limb muscle cross-sectional area and tissue fluid volume after transition from standing to supine.

Lower limbs show acute fluid shift in response to transition from upright to supine body position. It is hypothesized that this would affect tomographic estimations of muscle mass and composition. Seven healthy subjects were investigated during the initial 120 min of bed rest, using repeated computerized tomography (CT) and continuous bioelectrical impedance analysis (BIA). Thigh and calf muscle cross-sectional area (CSA) decreased (P < 0.05) by 1.9 and 5.5% whereas fat CSA decreased (P < 0.05) by 4.1 and 4.4%, respectively. Radiological density (RD) of muscle showed a simultaneous increase (P < 0.05) by 4.8% in calf but not (P > 0.05) in thigh. No changes occurred (P > 0.05) in muscle or fat CSA or muscle RD in either thigh or calf between the first and second hour of bed rest. Fluid shift, as estimated by BIA, showed an exponential decay in thigh (tau th = 30 min) and calf (tau c2 = 37 min) by 2.5 and 8.7%, respectively, from first to 120 min of bed rest. Moreover, the calf showed an initial rapid (tau c1 = 8 s) 2.2% decrease. The demonstrated short-term changes in leg CSA were more pronounced in the calf than in the thigh. They were similar in muscle and subcutaneous fat. These fluid shifts merit consideration when tomographic imaging techniques are used to estimate muscle mass and composition.

Adult↗
PubMed1992

Designing methods for musculoskeletal conditioning in weightlessness.

There is an immediate need to find methods to combat the skeletal muscle deconditioning that occurs in microgravity. Important features to be considered for any ergometer or exercise method to be used as a countermeasure against musculoskeletal deconditioning in space include heavy muscular loading of the postural muscles of the lower limbs and that eccentric and concentric muscle activations can be performed. Those are major requirements to produce optimal gains in strength and muscle mass at 1-g and probably to counteract muscle atrophy and strength loss in microgravity. Resistance exercise with a strength-ergometer, using the fly-wheel principle was carried out at a low oxygen cost and required no external power supply. We have developed a resistance training system employing this ergometer so that force and power production easily can be monitored and calibrated. It is suggested that the features of this ergometer meet the presented requirements for use during long-term space missions.

Animals↗
PubMed1991

Effects of lower limb unloading on skeletal muscle mass and function in humans.

A model to simulate effects of microgravity on skeletal muscle mass and function in humans has been developed. Unilateral lower limb unloading that allowed ankle, knee, and hip joint mobility was conducted in six healthy men by suspending one lower limb and having the subjects walk on crutches. They performed maximal unilateral concentric or eccentric quadriceps actions at different angular velocities before and after 4 wk of suspension and after 4 days and after 7 wk of uncontrolled recovery. Peak torque (PT) and angle-specific torque (AST) were measured. Muscle cross-sectional area (CSA) and radiological density (RD) of the thigh were assessed by means of computerized tomography. Concentric and eccentric PT and AST across speeds decreased (P less than 0.05) by 22 and 16%, respectively, in response to unloading. At 4 days of recovery PT (-11%) and AST (-7%) were still lower (P less than 0.05) than before. Muscle CSA and RD decreased (P less than 0.05) by 7 and 6%, respectively. After 7 wk of recovery PT, AST, CSA, and RD had returned to normal. The control limb showed no changes over the experimental period except for a 6% decrease (P less than 0.05) in RD. It is suggested that this human model of unloading could serve to simulate effects of microgravity on skeletal muscle mass and function because reductions in muscle mass and strength were of similar magnitude to those produced by bed rest.

Adult↗