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PubMed1981

Energy cost of submaximal isometric concentrations in cat fast and slow twitch muscles.

The purpose of the present investigation was to compare the net energy cost incurred by cat soleus (slow twitch muscle) and medial gastrocnemius predominantly fast twitch muscle) muscles for isometric contractions. For this, a computer-controlled sequential stimulation system was employed that enabled fused isometric contractions at frequencies of motor unit discharge within the normal physiological range. This allowed submaximal isometric contractions to be maintained at tensions of 10%, 25%, 50% and 75% of the initial strength of each muscle (tetanic tension of the unfatigued muscle determined at the beginning of each experiment). Total net energy cost was greater for the gastrocnemius than for the soleus muscle at each tension studied. For both muscles, the metabolism shifted toward anaerobic pathways at higher contraction tensions. But in comparison to the soleus muscle, the gastrocnemius muscle consistently had a greater percentage of its total net energy cost provided by anaerobic glycolysis rather than aerobic metabolism; for the gastrocnemius and soleus muscles the percent of the total metabolism from anaerobic pathways was 74% and 18% during the 10% contraction, 96% ad 84% during the 75% contraction for the medial gastrocnemius and soleus muscles respectively.

Animals↗

PubMed1987

The influence of straining maneuvers on the pressor response during isometric exercise.

Experiments were performed to determine to what extent increments in esophageal and abdominal pressure would have on arterial blood pressure during fatiguing isometric exercise. Arterial blood pressure was measured during handgrip and leg isometric exercise performed with both a free and occluded circulation to active muscles. Handgrip contractions were exerted at 33 and 70% MVC (maximum voluntary contraction) by 4 volunteers in a sitting position and calf muscle contractions at 50 and 70% MVC with the subjects in a kneeling position. Esophageal pressure measured at the peak of inspirations did not change during either handgrip or leg contractions but peak expiratory pressures increased progressively during both handgrip and leg contractions as fatigue occurred. These increments were independent of the tensions of the isometric contractions exerted. Intra-abdominal pressures measured at the peak of either inspiration or expiration did not change during inspiration with handgrip contractions but increased during expiration. During leg exercise, intraabdominal pressures increased during both inspiration and expiration, reaching peak levels at fatigue. The arterial blood pressure also reached peak levels at fatigue, independent of circulatory occlusion and tension exerted, averaging 18.5-20 kPa (140-150 mm Hg) for both handgrip and leg contractions. While blood pressure returned to resting levels following exercise with a free circulation, it declined by only 2.7-3.8 kPa after leg and handgrip exercise, respectively, during circulatory occlusion. These results indicate that straining maneuvers contribute 3.5 to 7.8 kPa to the change in blood pressure depending on body position.

Blood Pressure↗

PubMed1990

Physiological response in the forearm during and after isometric intermittent handgrip.

The aim of the present paper was to study the development of fatigue during isometric intermittent handgrip exercise. Using a handgrip dynamometer, four combinations of contraction-relaxation periods were studied (10 + 10, 10 + 5, 10 + 2 s and continuous contraction) at three contraction intensities (10, 25 and 40% maximum voluntary contraction, MVC). Local blood flow (BF) in the forearm (venous occlusion plethysmography) was followed before, during and after the exercise period. Electromyography (EMG) (frequency analysis) and the perceived effort and pain were recorded during the exercise period. Forearm BF is insufficient even at isometric contractions of low intensity (10% MVC). The results indicate that vasodilating metabolites play an active role for BF in low-intensity isometric contractions. It is shown that maximal BF in the forearm during relaxation periods (25-30 ml.min-1.100 ml-1) is already reached at 25% MVC. Only intermittent exercise at 10% MVC and (10 + 5 s) and (10 + 10 s) at 25% MVC was considered acceptable with regard to local fatigue, which was defined as a switch of local BF to the post-exercise period, a decrease in the number of zero-crossings (EMG) and marked increases in subjective ratings.

Adult↗

PubMed1995

Effect of prior isometric muscle action on concentric torque output during plantar flexion.

The influence of different levels of prior isometric muscle action on the concentric torque output during plantar flexion was examined at two angular velocities (60 degrees.s-1 and 120 degrees.s-1) in ten healthy female subjects. The levels of the prior muscle actions were 25%, 50%, 75% and 100% of the maximal voluntary isometric contraction (MVIC). A KINetic-COMmunicator II dynamometer was used to measure torque output during plantar flexion within a range of motion of 78 degrees-120 degrees of the ankle joint. Simultaneous recordings of electromyograms (low-pass filtered and rectified) were obtained from the gastrocnemius medialis muscle and the soleus muscle. Torque-angle curves were made for the plantar flexions using different prior muscle actions. Up to 75% of MVIC, the torque output in the first part of the range of motion increased with the level of the prior isometric muscle action; at higher levels of MVIC the torque did not appear to increase any further. Later in the range of motion, after 24 degrees in the plantar flexion at a velocity of 60 degrees.s-1 and 31 degrees at 120 degrees.s-1, the prior muscle actions had no further influence. No increase was found in the electromyograms, with one exception, during the concentric movements when preceded by higher levels of MVIC. It would seem therefore that the increase in torque output early in the range of motion cannot be explained on the basis of differences in electrical muscle activation in this study.

Adult↗

PubMed1988

Changes in strength and cross sectional area of the elbow flexors as a result of isometric strength training.

Changes in strength and size of the elbow flexor muscles have been compared during six weeks of isometric strength training in six male and six female subjects. Isometric training of one arm resulted in a significant increase in isometric force (14.5 +/- 5.1%, mean +/- SD, n = 12). No differences were seen in the response of male and female subjects. The extent of the change was similar to that reported for training studies of other muscles, thus refuting the suggestion that the elbow flexors may be especially amenable to training. Biceps and brachialis cross-sectional area (CSA) was measured from mid-upper arm X-ray computerized tomography before and after training. Muscles increased in area (5.4 +/- 3.8%) but this was smaller than, and not correlated with, the increase in strength. The main change in the first six weeks of strength training was therefore an increase in the force generated per unit cross-sectional area of muscle. The arrangement of fibres in the biceps is nearly parallel to the action of the muscle and it is argued that the increase in force per unit cross-sectional area is unlikely to be due to changes in the pennation of the muscle fibres as has been suggested for other muscles.

Adult↗

PubMed1986

Levels of serum creatine kinase and myoglobin in women after two isometric exercise conditions.

The purpose of this study was to measure serum creatine kinase (CK) activity and serum myoglobin (MG) concentrations in women after two unilateral isometric knee extension exercises. Forty maximal voluntary contractions (MVC) were held for 10 s, with either a 5 s (10:5) or 20 s 10:20 exercise (349.4 +/- 66.1 mU . ml-1) and 6 h and MG values were measured pre, 0, 3, 6, and 18 h post exercise. For CK, the highest post exercise values were observed at 6 h following the 10:20 exercise (349.4 +/- 66.1 mU . ml-1) and 6 h following the 10:5 exercise (194.1 +/- 18.6 mU . ml-1). For MG, the highest values were found 3 h after the 10:20 exercise (148.9 +/- 61.7 ng . ml-1) and 6 h after the 10:5 exercise (67.3 +/- 10.9 ng . ml-1). Serum CK and MG levels were significantly greater (p less than 0.01) after the 10:20 exercise bout. The data demonstrate that CK and MG values for women increase significantly after isometric exercise. Since greater tension levels were maintained during the 10:20 exercise it is hypothesized that increased serum CK and MG values after isometric exercise may be related to the tension generated by the contracting muscle.

Adult↗

PubMed2003

Bicoherence analysis of quadriceps electromyogram during isometric knee extension.

Bicoherence analysis is applied to electromyogram (EMG) data for the vastus lateralis quadriceps muscle of 18 adult male subjects for isometric knee extension exercise. Bicoherence spectra display ridge-like features that are indicative of deterministic chaotic behaviour and similar to those reported for normal electrocardiogram and electroencephalogram bicoherence spectra. No other obvious features are visually identified within bicoherence spectra in response to the stimulus of isometric tension. Histograms that show the occurrence of constituent EMG frequencies associated with the strongest bicoherence display subtle fluctuations. Validation tests that include the analysis of white noise data show these fluctuations to most likely be a consequence of the normal time evolution of a deterministic chaotic process. The finding suggests that second-order phase coupling is not pronounced between any particular bands of constituent EMG frequencies for the vastus lateralis EMG generation process during the specified isometric task. Previous studies into bicoherence analysis of EMG data are not apparent in the literature for comparison. Since nonlinear processes are known, through mechanomyogram bicoherence analysis, to be significant within active muscle fibre twitch summation patterns, the finding does not exclude the potential for bicoherence analysis to complement standard EMG frequency analysis techniques in the area of sports rehabilitation and medicine. Further investigation is required to establish whether this potential exists. An introduction to bicoherence analysis theory is also presented.

Adult↗

PubMed2005

Effect of combined variation of force amplitude and rate of force development on the modulation characteristics of muscle activation during rapid isometric aiming force production.

Studies of rapid target-directed limb movements have suggested that various control schemes can be defined by the modulation pattern of the muscle activity. The present study was aimed to address the question regarding the extent to which a simultaneous control of force amplitude, and rate of force development influences the modulation characteristics of muscle activation associated with producing rapid isometric aiming forces at the elbow joint. The subjects were instructed to produce rapid isometric force pulses to three different force amplitudes (15, 35, and 55% of their maximal voluntary contractions) under systematically varied force-rate conditions ranging from a fast and accurate force-rate to the fastest force-rate possible. The results showed that larger force amplitudes were achieved by increasing the rate of force development (d F/d t) while the time to peak force remained relatively constant. The magnitude of the electromyographic (EMG) burst systematically increased as a function of force amplitude at all force-rate conditions. The primary finding was that the characteristic of the EMG burst duration associated with different force amplitudes showed a significant difference among force-rate conditions. Under a fast and accurate force-rate condition, the duration of the agonist burst increased linearly with force amplitude. A gradual transition into a fixed duration of the agonist burst then was observed over the remaining three force-rate requirements. With increasingly faster force-rates, there were no changes in the agonist burst duration over three force amplitudes. These results indicate that the combined variations in force amplitude and force-rate examined relative to the most rapid force-rate influence the control patterns for the muscle activation during the fast isometric force production. Changes in the EMG modulation patterns observed are likely due to the constraints imposed by muscle contractile properties.

Adult↗

PubMed2006

Discharge rate during low-force isometric contractions influences motor unit coherence below 15 Hz but not motor unit synchronization.

The purpose of the study was to determine whether pairs of motor units that discharge action potentials at different rates during isometric contractions exhibit different levels of motor unit synchronization or coherence. Twelve subjects (28.6 +/- 6.1 years) performed isometric contractions at target forces slightly above the recruitment threshold (1.02-20.9%) of an isolated motor unit. Based on audio feedback, subjects maintained a relatively constant discharge rate of the isolated unit for about 80 s. Intramuscular electrodes were used to record the discharge of 47 pairs of motor units at rates that ranged from 8.07 to 13.6 pps. Correlated discharge between pairs of motor units was quantified with the common input strength (CIS) index, k' index, and coherence spectrum. Greater discharge rates across pairs of motor units were predicted (R2 = 0.36, P < 0.001) by higher coherence from 8 to 13 Hz (r = -0.52) and lower coherence from 0 to 4 Hz (r = 0.37). Indexes of motor unit synchronization (CIS and k') were strongly associated with motor unit coherence from 16 to 32 Hz (CIS: R2 = 0.63; k': R2 = 0.4; P = 0.001). The CIS index of motor unit synchronization and the motor unit coherence from 16 to 32 Hz did not vary with discharge rate. In contrast, the k' index of motor unit synchronization declined with discharge rate (r2 = 0.20, P = 0.001). Furthermore, greater discharge rates across pairs of motor units were accompanied by higher motor unit coherence in the 8-13 Hz band and lower motor unit coherence in the 0-4 Hz band. These results demonstrate that differences in discharge rate between pairs of motor units in first dorsal interosseus during low-force, isometric contractions were associated with modulation of the correlation in the discharge times of the two motor units at frequencies less than 15 Hz.

Acoustic Stimulation↗

PubMed2002

The effect of ageing in spinal cord injured humans on the blood pressure and heart rate responses during fatiguing isometric exercise.

Groups of 50 healthy male controls and 50 subjects suffering from paraplegia (aged 20-65 years) were examined as to the inter-relationships between age, paraplegia and the strength, endurance, blood pressure and heart rate responses to fatiguing isometric exercise. Contractions were maintained in both groups under voluntary effort and through a contraction induced by electrical stimulation in the paraplegic group. All contractions were maintained to fatigue at a tension of 40% of the maximal muscle strength in either the handgrip or quadriceps muscles. Muscle strength of the handgrip was higher in the paraplegic subjects than in the controls, averaging 589 N and 463 N, respectively for the two groups. In contrast, quadriceps leg extension strength averaged 696 N in the controls and 190 N in the paraplegic groups; for both groups, ageing was associated with a reduction in muscle strength. While leg endurance was less in the paraplegic group than the control group, handgrip endurance was similar in the two groups, endurance increasing with ageing in both the controls and paraplegics. Both systolic and diastolic blood pressures increased at rest in paraplegic and control subjects with age. The magnitude of the pressor response to exercise also increased with age. This was true during both voluntary exercise and exercise induced through electrical stimulation in the paraplegic groups. The heart rate response (change in heart rate during exercise) to a fatiguing isometric handgrip contraction decreased by about 50% between the ages of 20 and 60 years in both the controls and paraplegics for isometric handgrip exercise. In contrast, heart rate changed little with age during contractions of the quadriceps muscle in paraplegics which were induced by electrical stimulation.

Adult↗

PubMed2002

Delayed reoxygenation after maximal isometric handgrip exercise in high oxidative capacity muscle.

We hypothesized that after maximal short-term isometric exercise, when O(2) demand is still high and O(2) supply is not fully activated, higher oxidative capacity muscle may exhibit slower muscle reoxygenation after the exercise than low oxidative capacity muscle. Seven healthy male subjects performed a maximal voluntary isometric handgrip exercise for 10 s. The reoxygenation rate after the exercise (Reoxy-rate) in the finger flexor muscle was determined by near infrared continuous wave spectroscopy (NIRcws) while phosphocreatine (PCr) was measured simultaneously by (31)P magnetic resonance spectroscopy. Muscle oxygen consumption (muscle VO(2)) and muscle oxidative capacity were evaluated using the rate of PCr resynthesis post-exercise. The forearm blood flow (FBF) index at the end of exercise was measured using NIRcws. There was a significant positive correlation between the Reoxy-rate, which ranged between 0.53% s(-1) and 12.47% s(-1), and the time constant for PCr resynthesis, which ranged between 17.8 s and 38.3 s (r(2)=0.939, P<0.001). At the end of the exercise, muscle VO(2) exceeded the resting level by approximately 25-fold, while the FBF index exceeded the resting level by only 3-fold on average. The Reoxy-rate closely correlated with muscle VO(2) (r(2)=0.727, P<0.05), but not with the FBF index. Also, the estimated O(2) balance (muscle VO(2) index/FBF index) was negatively correlated with the Reoxy-rate (r(2)=0.820, P<0.001). These results support our hypothesis that higher oxidative capacity muscle shows slower muscle reoxygenation after maximal short-term isometric exercise because the Reoxy-rate after this type of exercise may be influenced more by muscle VO(2) than by O(2) supply.

Adaptation, Physiological↗

PubMed2004

Passive hyperthermia reduces voluntary activation and isometric force production.

It has been suggested that a critically high body core temperature may impair central neuromuscular activation and cause fatigue. We investigated the effects of passive hyperthermia on maximal isometric force production (MVC) and voluntary activation (VA) to determine the relative roles of skin (T(sk)) and body core temperature ( T(c)) on these factors. Twenty-two males [VO(2max)=64.2 (8.9) ml x kg(-1) min(-1), body fat=8.2 (3.9)%] were seated in a knee-extension myograph, then passively heated from 37.4 to 39.4 degrees C rectal temperature (T(re)) and then cooled back to 37.4(o)C using a liquid conditioning garment. Voluntary strength and VA (interpolated twitch) were examined during an isometric 10-s MVC at 0.5 degrees C intervals during both heating and cooling. Passive heating to a T(c) of 39.4(o)C reduced VA by 11 (11)% and MVC by 13 (18)% (P<0.05), but rapid skin cooling, with a concomitant reduction in cardiovascular strain [percentage heart rate reserve decreased from 64 (11)% to 29 (11)%] and psychophysical strain did not restore either of these measures to baseline. Only when cooling lowered T(c) back to normal did VA and MVC return to baseline (P<0.05). We conclude that an elevated T(c) reduces VA during isometric MVC, and neither T(sk) nor cardiovascular or psychophysical strain modulates this response. Results are given as mean (SD) unless otherwise stated.

Adaptation, Physiological↗

PubMed2005

Behaviour of the human gastrocnemius muscle architecture during submaximal isometric fatigue.

The purpose of this study was to examine whether the human gastrocnemius medialis (GM) fascicle length and pennation angle alter during a sustained submaximal isometric plantar flexion. Fourteen male subjects performed maximal voluntary plantar flexions (MVC) on a dynamometer before and after a fatiguing task. This task consisted of a sustained submaximal isometric fatiguing contraction (40% MVC) until failure to hold the defined moment. Ultrasonography was used to visualise the muscle belly of the GM. Leg kinematics were recorded (120 Hz) to calculate the joint moment using inverse dynamics. The exerted moments and the EMG signals from GM and lateralis, soleus and tibialis anterior were measured at 1,080 Hz. The root mean square (RMS) of the EMG signal of the three triceps surae muscles increased significantly (P < or = 0.05) between 17% and 28% with fatigue. Further, the fascicle length of the GM significantly decreased from 47.1 +/- 8.0 mm at the beginning to 41.8 +/- 6.7 mm at the end of fatigue and the pennation angle increased from 23.5 +/- 4.1 degrees to 26.3 +/- 2.2 degrees (P < or = 0.05). The changes in fascicle length and pennation angle of the GM during the contraction can influence the force potential of the muscle due to the force-length relationship and the force transmission to the tendon. This provides evidence on that an additional mechanical mechanism, namely tendon creep, can contribute to the increase in the EMG activity of the GM during submaximal isometric sustained contractions.

Aged↗

PubMed1998

The effect of leg flexion angle on the mechanomyographic responses to isometric muscle actions.

The purpose of this investigation was to examine the effect of leg flexion angle on the relationship between mechanomyographic (MMG) amplitude and isometric torque production. Adult males (n = 9) performed isometric muscle actions of the leg extensors at 25, 50, 75, and 100 percent maximal voluntary contraction (%MVC) on a calibrated CYBEX 6000 dynamometer at 25, 50, and 75 degrees below full extension. A piezoelectric MMG recording device was placed over the mid-portion of the rectus femoris. At 25 degrees of leg flexion, the MMG amplitude increased to 100%MVC. At 50 and 75 degrees of leg flexion, however, MMG amplitude increased to 75%MVC, and then did not change significantly (P > 0.05) between 75 and 100%MVC. These findings indicate that the MMG amplitude-isometric torque relationship is joint angle specific and may be the result of leg flexion angle differences in: (1) muscle stiffness, or (2) motor unit activation strategies.

Adult↗

PubMed1999

Human isometric force production and electromyogram activity of knee extensor muscles in water and on dry land.

This study was designed to determine trial-to-trial and day-to-day reproducibility of isometric force and electromyogram activity (EMG) of the knee extensor muscles in water and on dry land as well as to make comparisons between the two training conditions in muscle activity and force production. A group of 20 healthy subjects (12 women and 8 men) were tested three times over 2 weeks. A measurement session consisted of recordings of maximal and submaximal isometric knee extension force with simultaneous recording of surface EMG from the vastus medialis, vastus lateralis and biceps femoris muscles. To ensure identical measurement conditions the same patient elevator chair was used in both the dry and the wet environment. Intraclass correlation coefficients (ICC) and coefficients of variation (CV) showed high trial-to-trial (ICC = 0.95-0.99, CV = 3.5%-11%) and day-to-day reproducibility (ICC=0.85-0.98, CV=11%-19%) for underwater and dry land measurements of force and EMG in each muscle during maximal contractions. The day-to-day reproducibility for submaximal contractions was similar. The interesting finding was that underwater EMG amplitude decreased significantly in each muscle during maximal (P < 0.01-P < 0.001) and submaximal contractions (P < 0.05-P < 0.001). However, the isometric force measurements showed similar values in both wet and dry conditions. The water had no disturbing effect on the electrodes as shown by slightly lowered interelectrode resistance values, the absence of artefacts and low noise levels of the EMG signals. It was concluded that underwater force and EMG measurements are highly reproducible. The significant decrease of underwater EMG could have electromechanical and/or neurophysiological explanations.

Adult↗

PubMed2001

Electromyogram power spectrum and features of the superimposed maximal M-wave during voluntary isometric actions in humans at different activation levels.

The frequency characteristics of the electromyogram (EMG) power spectrum, such as the median or the mean power frequency, as well as the duration of the muscle compound action potential response to a single supramaximal electrical stimulus (maximal M-wave) may both be related to the conduction velocity (CV) of the muscle fibre. To investigate this further, we studied in ten male subjects: the EMG of the vastus lateralis, vastus medialis and rectus femoris muscles during maximal isometric knee extensions at 40%, 60%, 80% and 100% of maximal voluntary contraction and also the maximal M-wave, elicited by a single supramaximal stimulus to the femoral nerve, of the same muscles at rest or superimposed on the same levels of voluntary contraction. The EMG was recorded during the constant force phase of the voluntary contractions, the duration of which was 2.5-4 s, with a 1.5 min pause between contractions. The average EMG (aEMG) and the median frequency (MF) were then calculated. The results indicated that as aEMG increased with increase in force, MF remained unchanged. However, while the amplitude of the M-wave was not affected, the duration of the M-wave was shorter as the force level increased. The duration of the M-wave may be affected by recruitment of faster motor units, by increased firing rate of the active units and by changes in the muscle fibre length. The shorter duration of the M-wave observed at higher force levels was not, however, accompanied by a corresponding increase in MF. The MF could not therefore be used as a parameter to reflect the changes in voluntary muscle activation and CV. When MF was calculated by overlapping the fast Fourier transform (FFT) windows (0.4 s long window moved data point by data point to the right) for 1 s periods of the isometric plateau phase at each force level, the difference between the lowest and the highest MF was quite substantial. These variations suggest that FFT window placement, i.e. which part of the signal is chosen for the analyses, may play an important role even in isometric situations.

Adult↗

PubMed2001

Effect of human exposure to altitude on muscle endurance during isometric contractions.

The aim of this study was to evaluate the influence of exposure to altitude on muscle endurance during isometric contractions. Six sedentary subjects were studied. Surface electromyograph (sEMG) activity was recorded from the right biceps brachii (BB) during exhausting isometric exercise at 80% maximal voluntary contraction. Experiments were performed before, during and 6 months after a 12 day stay at the EV-K2 laboratory (Nepal, 5,050 m above sea level). From the sEMG signals from BB, the median frequencies (fmed) were computed for consecutive 1 s epochs. The sEMG was also analysed using a non-linear tool, the recurrence quantification analysis, and the percentage of determinism (%DET) was then calculated. The haemoglobin saturation significantly decreased at altitude. The mean (SD) BB endurance time decreased from 22.4 (4) s to 18.3 (4.7) s (P < 0.05). After exposure to altitude a significant variation in fmed and %DET slopes was observed. We concluded that during the first period of acclimatisation at altitude there was an impairment of isometric muscle endurance performance and there was also evidence of a modified myoelectric activity pattern suggesting a greater fatigability of the neuromuscular system.

Adult↗

PubMed2001

Blood pressure and heart rate response to isometric exercise: the effect of spinal cord injury in humans.

The systolic (SP) and diastolic (DP) blood pressure and heart rate (HR) responses during a fatiguing isometric contraction of either the handgrip or quadriceps muscles was measured in 139 paraplegic patients divided into five groups (having injuries at T4, T12 and L1-L3 and suffering complete paraplegia and having injuries at T4 but showing incomplete hemiplegia or paraplegia) and 25 controls. While all handgrip exercise was maintained by voluntary effort, only the controls were able to make a voluntary contraction of their quadriceps muscles; the paraplegics had isometric contractions of their quadriceps muscles elicited by functional electrical stimulation (FES). The endurance of the handgrip exercise was not significantly different among the controls and any one of the five experimental groups (control group endurance = 151 s, average paraplegic group endurance = 141 s) while it was higher in the leg muscles (P < 0.05 controls 133 s, paraplegics 111 s). All subjects showed a linear increase in SP and DP throughout the duration of the handgrip exercise, pressure increasing from rest to fatigue by 55-56 mmHg. The controls, subjects with a complete and incomplete spinal cord injuries at T4 showed similar SP and DP increases during leg exercise, both the SP and DP response was eliminated in the T12 and L1-L3 injury groups. The HR increased during fatiguing isometric handgrip contractions from an average resting value of 82 to a maximum of 121 beats x min(-1) in both the controls and paraplegic subjects. However, while the HR increased to a slightly higher level of 127 beats x min(-1) at the end of the contraction of the leg muscles in the controls, the increase in HR during FES exercise was modest, increasing by an average of only 6 beats x min(-1) in the paraplegic group.

Adult↗