Maximal Voluntary Isometric Force Research Articles

Gender Differences after Downhill Running for Voluntary Isometric Contractions of Knee Extensor Muscles using Surface EMG

Introduction: We examined gender differences for performance and surface electromyograms (sEMG) of knee extensors 1hr after downhill running. Methods: Maximal voluntary isometric force (MVIF) and sEMG of vastus lateralis (VL) and vastus medialis (VM) muscles during 50%MVIF were measured in 8 males (22±4yr, 75.8±6.1kg, 179.2.0±5.0cm) and 8 females (27±8yr, 60.8±7.2kg, 166.3±5.0cm) before and 1 hr after downhill running [(5x8 min, -12%, 60%V max (females: 7.7±0.9km·h -1 , males: 10.4±0.5km·h -1 )]. Results: Males had higher MVIF values (674.3±59.8N versus 480.6±49.9N, P<0.001) and longer endurance times during 50%MVIF than females (78.7±24.1s versus 57.2±12.6s, P<0.05) before downhill running. After downhill running, MVIF deficits were similar (males: 11.7±7.2%, females: 7.5±7.7%) with no changes in endurance times during 50%MVIF. After the downhill run, there was a trend in females, but not males, of an increased ratio for the root mean square (RMS) values of the VL and VM muscles during MVIF testing by 23% (P=0.054). After the downhill run, females, but not males, lowered during 50%MVIF the change in RMS for VM from 48±32% to 30±31% and for VL from 36±23% to 21±18% (P<0.05). For males, a trend was observed for the change in median frequency in VL during 50%MVIF (P=0.05). After downhill running, females, altered the vastus medialis and vastus lateralis contributions to maximal isometric force production and the activity pattern of these muscles during submaximal isometric fatigue. Conclusion: Acute neuromuscular adaptations after downhill running occur during voluntary isometric contractions of knee extensor muscles in females, but not in males.

Sit-to-stand Test to Evaluate Knee Extensor Muscle Size and Strength in the Elderly: A Novel Approach

The present study examined whether a sit-to-stand score can be related to the force-generating capacity of knee extensor muscles. Fifty-seven subjects (28 men, 63.0+/-7.8 yrs, and 29 women, 64.2+/-7.5 yrs, means+/-SDs) performed a 10-repeated sit-to-stand test as fast as possible, on a steel molded chair. The time taken (T(sit-stand)) was measured with a manual stopwatch. The leg length (L), defined as the distance from the great trochanter of the femur to the malleolus lateralis, was measured using a tape. A power index of the test (P(sit-stand)) was calculated by using the following equation: P(sit-stand)=(L-0.4) x body mass x g x 10/T(sit-stand). The cross-sectional area of the quadriceps femoris muscle (CSA(KE)) and the maximal voluntary isometric knee extension force (F(KE)) were measured using MRI and a static myometer, respectively. There was no significant correlation between T(sit-stand) and each of CSA(KE) and F(KE). On the other hand, the P(sit-stand) was highly correlated with CSA(KE) and F(KE), even after the influence of body mass and L was statistically eliminated. These results indicate that P(sit-stand), derived from three variables of body mass, leg length, and time taken for a sit-to-stand test, can be a useful index to assess the force-generating capacity of the knee extensor muscles of elderly individuals.

The Valsalva Maneuver Revisited: The Influence of Voluntary Breathing on Isometric Muscle Strength

We assessed the effects of 4 voluntary breathing conditions on maximal voluntary isometric force of large muscle groups. Ten subjects performed maximum voluntary isometric contractions (MVICs) of knee flexion and extension, shoulder abduction and adduction, and elbow flexion and extension under all breathing conditions: normal breathing, forced inhalation, forced exhalation, and the Valsalva maneuver (VM). Forced exhalation significantly increased peak force during shoulder adduction, elbow extension, and knee extension MVIC tasks (p = 0.001, 0.024, and 0.002, respectively); the peak force during the Valsalva maneuver was not different from forced exhalation for all tested muscle groups. No voluntary breathing condition seemed to influence the peak force during the knee flexion, elbow flexion, and shoulder abduction MVIC tasks. The results demonstrate that voluntary breathing imposes a significant impact on isometric muscle strength. Given the increased cardiovascular risks associated with the Valsalva maneuver, it is highly recommended that forced exhalation be used during exercise at maximal levels, especially in repetitive repetitions.

Standardized voluntary force measurement in a lower extremity rehabilitation robot

BackgroundIsometric force measurements in the lower extremity are widely used in rehabilitation of subjects with neurological movement disorders (NMD) because walking ability has been shown to be related to muscle strength. Therefore muscle strength measurements can be used to monitor and control the effects of training programs. A new method to assess isometric muscle force was implemented in the driven gait orthosis (DGO) Lokomat. To evaluate the capabilities of this new measurement method, inter- and intra-rater reliability were assessed.MethodsReliability was assessed in subjects with and without NMD. Subjects were tested twice on the same day by two different therapists to test inter-rater reliability and on two separate days by the same therapist to test intra-rater reliability.ResultsResults showed fair to good reliability for the new measurement method to assess isometric muscle force of lower extremities. In subjects without NMD, intraclass correlation coefficients (ICC) for inter-rater reliability ranged from 0.72 to 0.97 and intra-rater reliability from 0.71 to 0.90. In subjects with NMD, ICC ranged from 0.66 to 0.97 for inter-rater and from 0.50 to 0.96 for intra-rater reliability.ConclusionInter- and intra- rater reliability of an assessment method for measuring maximal voluntary isometric muscle force of lower extremities was demonstrated. We suggest that this method is a valuable tool for documentation and controlling of the rehabilitation process in patients using a DGO.

Effects of Acupuncture on Symptoms and Muscle Function in Delayed-Onset Muscle Soreness

This study was done to investigate the effects of a standardized acupuncture treatment on symptoms and muscle function in exercise-induced delayed-onset muscle soreness (DOMS). A prospective, randomized, controlled, observer and subject-blinded trial was undertaken. Twenty-two (22) healthy subjects (22-30 years; 10 males and 12 females) were randomly assigned to three treatment groups: real acupuncture (deep needling at classic acupuncture points and tender points; n = 7), sham-acupuncture (superficial needling at nonacupuncture points; n = 8), and control (no needling; n = 7). DOMS of the nondominant elbow-flexors was experimentally induced through eccentric contractions until exhaustion. The outcome measures were pain perception (visual analogue scale; VAS; range: 0-10 cm), mechanical pain threshold (MPT; pressure algometer), and maximum isometric voluntary force (MIVF; force transducer). Treatment was applied immediately, 24 and 48 hours after DOMS induction. Measurements of MPT and MIVF were made prior to DOMS induction as well as before and after every treatment session. VAS data were acquired after DOMS induction as well as pre- and post-treatment. Final pain, MPT, and MIVF measurements were performed 72 hours after DOMS induction. Following nonparametric testing, there were no significant differences between groups in outcome measures at baseline. After 72 hours, pain perception (VAS) was significantly lower in the acupuncture group compared to the sham acupuncture and control subjects. However, the mean MPT and MIVF scores were not significantly different between groups. Although acupuncture seemed to have no effects on mechanical pain threshold and muscle function, it proved to reduce perceived pain arising from exercise-induced muscle soreness.

Effects Of Acupuncture On Delayed Onset Muscle Soreness (DOMS)

Delayed onset muscle soreness (DOMS) is a frequently observed phenomenon in recreational or experienced athletes. It is associated with tenderness, pain and impairments in muscle function which may interfere with training capacity and athletic performance. Although acupuncture might minimize signs and symptoms of DOMS, there is no consistent evidence. PURPOSE: To investigate the effects of a standardized acupuncture treatment on symptoms and muscle function in exercise-induced DOMS. METHODS: A prospective randomized controlled observer and patient-blinded trial was undertaken. Twenty-two healthy sport students (22-30 yrs.; 10 males & 12 females) were randomly assigned to three treatment groups: verum acupuncture (deep needling at classic acupuncture points and tender points; n=7), sham-acupuncture (superficial needling at non-acupuncture points; n=8) and control (no needling; n=7). DOMS of the non-dominant elbow-flexors was experimentally induced through eccentric contractions until exhaustion. The outcomes measures were pain perception (visual analogue scale; VAS; range: 0-100mm), mechanical pain threshold (MPT; pressure algometer), and maximum isometric voluntary force (MVIF; force transducer). Treatment was applied immediately, 24 and 48 hours after DOMS induction. Measurements of MPT and MIVF were made prior to DOMS induction as well as before and after every treatment session. VAS data were acquired post- induction as well as pre- and post-treatment. Final pain, MPT and MIVF measurements were performed 72 hours after DOMS induction. RESULTS: Following nonparametric testing, there were no significant differences between groups in outcome measures at baseline. After 72 hours, pain perception was significantly lower in the acupuncture group (mean ± SD: 5mm ± 7mm) compared to the sham-acupuncture (mean ± SD: 26mm ± 16mm) and control subjects (mean ± SD: 21mm ± 14mm) (p<0.05). However, the mean MPT and MIVF scores were not significantly different between groups. CONCLUSIONS: Although acupuncture seemed to have no effects on mechanical pain threshold and muscle function, it proved to reduce perceived pain arising from exercise-induced muscle damage. Future studies should examine the effectiveness of acupuncture in routine athletic care.

Maximal Voluntary Isometric Elbow Flexion Force during Unilateral versus Bilateral Contractions in Individuals with Chronic Stroke

The purpose of this study was to determine whether the phenomenon of bilateral deficit in muscular force production observed in healthy subjects and mildly impaired stroke patients also exists in patients with more chronic and greater levels of stroke impairment. Ten patients with chronic hemiparesis resulting from stroke performed unilateral and bilateral maximal voluntary isometric contractions of the elbow flexors. When the total force produced by both arms was compared, 12% less force was produced in the bilateral compared with unilateral condition (p=0.01). However, studying the effect of task conditions on each arm separately revealed a significant decline in nonparetic (p=0.01) but not paretic elbow flexor force in the bilateral compared with unilateral condition. Results suggest that a significant bilateral force deficit exists in the nonparetic but not the paretic arm in individuals with chronic stroke. Bilateral task conditions do not seem to benefit or impair paretic arm maximal isometric force production in individuals with moderate-severity chronic stroke.

Maximal voluntary isometric force is lower during bilateral compared to unilateral quadriceps contractions

Maximal voluntary isometric force is lower during bilateral compared to unilateral quadriceps contractions

Acute effect of percutaneous electrical stimulation of knee extensor muscles on isokinetic torque and power production performance

The aim of the present study was to examine the acute effect of a brief submaximal percutaneous electrical stimulation (PES) of the knee extensor (KE) muscles as a conditioning activity on the isokinetic peak torque (PT) and average power (AP). Eighteen male students aged 20-25 years performed maximal voluntary concentric isokinetic knee extensions at angular velocities of 60 and 180°/s in control (CON) trial (without prior PES application), followed by a PES trial after 30 min rest period. In PES trial, a conditioning submaximal (25% of the maximal voluntary isometric contraction force) isometric tetanic contraction of the KE muscles was induced by a 7 s direct PES at 100 Hz, interspersed after 3 min with testing of voluntary isokinetic performance. No significant differences in isokinetic knee extension PT and AP were observed between PES and CON trial at 60°/s. However, a significantly greater (p < 0.05) isokinetic PT (8.9%) and AP (8.2%) were observed in PES trial compared to CON trial at 180°/s. In conclusion, application of a brief high-frequency submaximal PES may enhance isokinetic strength and power of the KE at a moderate but not at a low angular velocity.

Effects of fatigue of elbow extensor muscles voluntarily induced and induced by electromyostimulation on multi-joint movement organization

To investigate the capacity of the central nervous system to integrate and differentiate two different muscular fatigue states, the present study examines the changes on multi-joint movement organization following muscular fatigue of elbow extensor muscles (triceps brachii) induced by voluntary versus electrically induced contractions. Twenty right-handed male volunteers performed throws in the horizontal plane before and after two fatiguing procedures. First, success rate of throws was not affected by fatigue neither after voluntary contractions, nor after electrically induced contractions. Despite similar reductions of the maximal voluntary isometric force and the median frequency of the electromyographic signal following both fatiguing protocols, voluntary contractions induced greater changes in muscle activation, kinematics and kinetics during throws than electrically induced contractions. The changes observed following voluntary contractions are interpreted as a compensatory strategy involving a greater contribution of the wrist. In contrast, the greater activation of the triceps brachii could compensate the weakness of this muscle induced by fatigue without any modification of the initial multi-joint movement organization.

Effects of Electrotherapy And Icing on Damaged Muscle During Repeated Sets Exercise

PURPOSE: This study investigated which modality would be the best way to improve the recovery of muscle function and immediately performance between two different sets of repeated bouts eccentric exercise. METHODS: Thirty-six non-weight-trained females (29.32 ± 3.58 yrs, 175.75 ± 3.76 cm, 77.00 ± 12.02 kg) participated in this study. All subjects performed the first set of 30 eccentric actions (ECC1) with non-dominate elbow flexors using the dumbbell that was set at 80% of the pre-ECC1 maximal voluntary isometric contraction force (MVC) level, and then subjects were randomly placed into cryotherapy (CTG; n = 12), electrical therapy (ETG; n = 12) or control (CON; n = 12) groups based on their MVC response to ECC1. Immediately after ECC1, cryotherapy and electrical theraphy groups were accepted cold pack and trans cutaneous electrical nerve stimulation (TENS) treatments, respectively, for an hours. Including CON, all subjects were repeated the same bout of 30 eccentric exercise (ECC2) after treatments. MVC were assessed before, immediately after both ECC1 and ECC2, and 2, 4, 7, and 10 days (D2, D4, D7, D10) after ECC1 for all groups. Serum creatine kinase muscle isoform (CK-MM) was collected before, and D2, D4, D7, and D1 0 for all groups. RESULTS: There was a significant further decrease (p <0.01) in MVC immediately after treatment when compared to pre-test for the ETG, but not in CTG and CON. The MVC for ETG were significant decrease than CTG (p <0.05) on day D4, D7, D10, were significant decrease than CON (p <0.05) on D7, D10. There were significant increase in CK-MM on D4, D7 (p <0.05) when compared to pre-test for the ETG, was increase on D4 (p <0.05) for CON, but no significant different between each day for CTG. The CK-MM for ETG were significant increase than CTG and CON on D2, D4, D7 and D10 (p <0.05), and no significant different between CTG and CON on any day. CONCLUSION: The long-term recovery outcomes showed cryotherapy is the most beneficial for muscle damage management between repeated sets, and the short-term outcomes showed cryotherapy and resting are beneficial to the muscle performance, such as muscle strength and active range of motion. Electrical therapy is disadventiaged to manage muscle damage between repeated sets exercise.

Effects of Passive Warm-Up With Ultrasound Diathermy on Exercise Performance and Muscle Damage

PURPOSE: This study investigated the effects of passive warm-up with ultrasound diathermy and heat packing on exercise performance and recovery on muscle damage. METHODS: Eighteen females (22.16±0.84yrs) participated in this study. All of them were involved into three groups as control group (CON), heat packing group (HP) and ultrasound group (USD). CON never received any warm-up protocol before eccentric exercise, HP received 15 minutes of superficial heat with electrical heat pack before exercise, and USD received 7 minutes of deep heat with ultrasound diathermy before exercise. Each subject processed 30 repeated bouts of eccentric exercise with 80% maximal voluntary isometric contraction force (MVC) level. Serum creatine kinase muscle isoform (CK-MM), MVC, range of motion (ROM) and cross section area of biceps brachii (CSA) were measured before, immediately after exercise and at 2nd, 4th, 7th, and 10th days post-exercise. RESULTS: When measuring serum CK-MM and CSA, there were no significant difference between CON, HP and USD (P > 0.05). When measuring ROM and MVC, there were significant difference between CON, HP and USD (p < 0.05).FigureCONCLUSION: Passive warm-up with ultrasound diathermy and heat packing have better performance in muscle strength and range of motion in eccentric exercise. According to the recovery procedure, Subjects of USD group took lesser damage on muscles than HP and CON. USD group had lesser swelling then other groups in recovery stage after eccentric contraction exercise.

Maximal force during eccentric and isometric actions at different elbow angles

The purpose of this study was to examine a course of force potentiation and/or inhibition during maximal voluntary eccentric action. Maximal voluntary force (MVC) of elbow flexion of ten healthy male volunteers was measured during isometric and isokinetic eccentric action starting from 80 degrees or 110 degrees and ending at 140 degrees elbow angle. Surface EMG was recorded from biceps brachii (BB) and brachioradialis (BR) muscles. Maximal voluntary eccentric force during the first 10 degrees of the movement was higher (P<0.001) than the maximal voluntary isometric preactivation force both in 80 degrees and in 110 degrees starting position at all three velocities (1, 2, and 4 rad s(-1)). The relative force potentiation was velocity dependent being smallest at the lowest stretching speed (P<0.01). Average EMG (aEMG) of BB and BR decreased as the joint angle increased both in eccentric and in isometric actions but the decrease in aEMG towards extension was somewhat higher in eccentric actions as compared to isometric. It was concluded that the force measured during the first 10 degrees of eccentric contraction always exceeded the maximal voluntary isometric preactivation force regardless of the joint angle or of the movement velocity. When maximal voluntary preactivation preceded the stretch, the relative force potentiation seemed to be greater at higher stretching velocities (velocity dependent) while at lower preactivation levels, the velocity dependence was not observed. Decreased muscle activation and lower maximal voluntary force towards the end of the movement suggested inhibition during maximal voluntary eccentric actions.

Test Methods to Detect Hip and Knee Muscle Weakness and Gait Disturbance in Patients With Hip Osteoarthritis

Rasch A, Dalén N, Berg HE. Test methods to detect hip and knee muscle weakness and gait disturbance in patients with hip osteoarthritis. Objective To evaluate test methods for hip and knee muscle weakness and gait disturbance. Design Test-retest. Setting Orthopedic university clinic. Participants Ten young (age, 36±6y) and 13 elderly (age, 69±8y) healthy volunteers and 11 patients (age, 69±8y) with unilateral hip osteoarthritis (OA) were tested for muscular strength. Twenty-five volunteers (age, 42±14y) underwent gait analysis. Interventions A dynamometer assessing maximal voluntary isometric force of hip and knee muscles and an optosensor walkway detecting limp were developed. Tests evaluated reproducibility and tolerance in patients with OA and elderly subjects. Main Outcome Measures Relative coefficient of variation (CV%) and force (in newtons). Results CV% for unilateral strength measurements ranged from 7% to 12% for specific muscle groups. CV% for gait parameters ranged from 4% to 8%, except for the double-support phase. Tests were well tolerated, and no patient had to discontinue because of fatigue. Differences related to sex, age, and disease were detected. Conclusions Our dynamometer system provides reliable measurements of hip and knee muscle strength in young and old people, and variation is comparable to previous data. Our photocell technique for gait analysis is reliable in people with normal gait. Both methods are attractive because they are affordable, nonstationary, and easy to use.

Diurnal changes in the amplitude of the Hoffmann reflex in the human soleus but not in the flexor carpi radialis muscle

Changes in the reflex amplitude throughout the day have been observed in non-human mammals. The present experiment tested whether diurnal fluctuations also occur in humans. Hoffmann reflex (H-reflex) amplitude was measured in soleus and flexor carpi radialis (FCR) muscles from the data collected over a 12-h period between 7:00-9:00 a.m. and 7:00-9:00 p.m. At 4-h intervals, M/H recruitment curves were obtained, and two measures of H-reflex excitability were calculated. The maximal H-reflex (H (max)) was calculated as the average of the three largest H-reflexes. H-reflexes were also sampled from the ascending limb of the M/H recruitment curve (H (A), n=10), with a corresponding M-wave of 5% M (max). All values were normalized to the maximal M-wave (M (max)). Soleus H-reflex amplitude and plantar flexion maximal voluntary isometric contraction force (MVIC) were significantly smaller (p<0.05) in the morning (H (max)=57.2% M (max), H (A)=42.3%, M (max), MVIC=162.1 Nm) than in the evening (H (max)=69.1% M (max), a 20.1% increase, H (A)=54.1% M (max), a 27.4% increase and MVIC=195.8 Nm, a 20.8% increase). In contrast, FCR H-reflex amplitude and FCR MVIC were unchanged across all testing sessions. The data show that diurnal fluctuations are present in the amplitude of the human soleus but not in the FCR H-reflex. Diurnal fluctuation in the human soleus H-reflex amplitude must be considered when interpreting H-reflex data, especially when a repeated measures design spanning several days is utilized.

Changes in the force development characteristics of muscle following repeated maximum force and power exercise

There is some evidence to suggest that ability to develop force in skeletal muscle can be improved for a short period following repeated maximal strength exercise. Some studies have suggested the phenomenon known as post-activation potentiation (PAP) to explain this immediate response to such exercise. However, little is known about the physical and temporal characteristics of the changes in muscle function due to PAP when induced using whole-body maximal strength exercise. The purpose of this study was to establish the physical and temporal characteristics of PAP of muscle function in elite male athletes following maximum strength and power exercise. Fifteen participants performed one of repeated maximal strength exercise or maximal power exercise or a control protocol on separate occasions. Changes in maximum isometric voluntary force (iMF), maximum isometric rate of force development (iRFD) and maximum vertical counter-movement jump (CMJ) were assessed. Results suggest that post-activation potentiation of iRFD occurs but is preceded by an initial suppression of force development capability following repeated maximal strength exercise. Following repeated maximal power exercise, however, post-activation potentiation of iRFD occurs immediately but is not seen over as long a period as that observed following maximal strength exercise. These results suggest that post-activation potentiation does bring about increased force development capability following intense exercise and that the temporal profile of the post-activation potentiation changes with intensity of the exercise used to induce it.

Quantitating progression in ALS

The authors prospectively studied the value of clinical and neurophysiologic measurements in assessing progression in ALS. Motor unit number estimation (MUNE) and the neurophysiologic index (NI) were significantly correlated with ADM strength (maximal voluntary isometric contraction force in the abductor digiti minimi muscle [MVIC-ADM]). MUNE and the NI were reliable, but the NI showed a lower variation. On assessing progression at 3, 6, and 12 months, MUNE, NI, and MVIC-ADM showed the highest rate of change. The NI is a potentially useful new neurophysiologic measurement.

Effects of supra‐physiological changes in human ovarian hormone levels on maximum force production of the first dorsal interosseus muscle

The purpose of this study was to investigate the effects of supra-physiological changes in ovarian hormone levels on maximum force production in two conditions, one physiological (pregnancy) and one pseudo-physiological (in vitro fertilization (IVF) treatment). Forty IVF patients were tested at four distinct stages of treatment and 35 women were tested during each trimester of pregnancy and following parturition. Maximum voluntary isometric force per unit cross-sectional area of the first dorsal interosseus muscle was measured. Plasma concentrations of total and bioavailable oestradiol and testosterone were measured, in addition to the total concentrations of progesterone and human chorionic gonadotropin. Despite significant changes in the concentrations of total progesterone, 17beta-oestradiol, bioavailable oestradiol and testosterone between phases, strength did not change significantly throughout IVF treatment (1.30+/-0.29, 1.16+/-0.38, 1.20+/-0.29 and 1.26+/-0.34 N mm-2, respectively, in the 4 phases of IVF treatment). Force production was significantly higher during the second trimester of pregnancy than following childbirth (1.33+/-0.20 N mm-2 at week 12 of pregnancy, 1.51+/-0.42 N mm-2 at week 20, 1.15+/-0.26 N mm-2 at week 36 and 0.94+/-0.31 N mm-2 at week 6 postnatal) but was not significantly correlated with any of the hormones measured. These data suggest that extreme changes in the concentrations of reproductive hormones do not affect the maximum force-generating capacity of young women.

Assessment of skeletal muscle fatigue in men with coronary artery disease using surface electromyography during isometric contraction of quadriceps muscles

Gayda M, Merzouk A, Choquet D, Ahmaidi S. Assessment of skeletal muscle fatigue in men with coronary artery disease using surface electromyography during isometric contraction of quadriceps muscles. Objective To evaluate whether using surface electromyography to assess skeletal muscle fatigue during an isometric exercise has the potential to be clinically useful in patients with coronary artery disease (CAD). Design Double sample comparative study. Setting Cardiac rehabilitation service in France. Participants Sixteen men with documented CAD and 9 age-matched healthy men. Interventions Assessment of quadriceps skeletal muscle fatigue on an isokinetic apparatus with surface electromyography measurements and a symptom-limited exercise test in a laboratory. Main outcome measures The maximal voluntary isometric force (MVIF) of the quadriceps was quantified as a measure of muscle strength and isometric endurance was defined as the time required to sustain a contraction at 50% of MVIF until exhaustion. Surface electromyography signals were recorded from the vastus lateralis, rectus femoris, and vastus medialis during isometric endurance. The root mean square (RMS) and the median frequency (MF) were directly calculated on a computer and then normalized (as a percentage of the initial value). Results Muscle strength did not differ significantly between the patients with CAD and the healthy subjects (229±21N/m vs 228±52N/m), but isometric endurance was reduced (64±17s vs 90±7s, P<.01). The RMS values showed a significantly higher increase in the healthy subjects versus the patients with CAD for the vastus lateralis and vastus medialis ( P<.001). The MF values were significantly lower for the vastus lateralis, rectus femoris ( P<.01), and vastus medialis ( P<.05) in patients with CAD compared with the healthy subjects. Conclusions Skeletal muscle fatigue occurs sooner in men with CAD relative to matched healthy men, despite similar muscle strength. This finding may be the result of an abnormality of skeletal muscle function and may play an important role in measuring functional capacity. In addition, it may be a useful tool to assess the efficacy of cardiac rehabilitation interventions.

Acute Hormonal Responses to Heavy Resistance Exercise in Strength Athletes Versus Nonathletes

The aim of the present study was to investigate acute hormonal and neuromuscular responses and recovery in strength athletes versus nonathletes during heavy resistance exercise performed with the forced and maximum repetitions training protocol. Eight male strength athletes (SA) with several years of continuous resistance training experience and 8 physically active but non-strength athletes (NA) volunteered as subjects. The experimental design comprised two loading sessions: maximum repetitions (MR) and forced repetitions (FR). MR included 12-RM squats for 4 sets with a 2-min recovery between sets. In FR the initial load was higher than in MR so that the subject could lift approximately 8 repetitions by himself and 4 additional repetitions with assistance. Before and after the loading protocols, blood samples were drawn to determine serum testosterone, free testosterone, cortisol and growth hormone concentrations, and blood lactate. Maximal voluntary isometric force and EMG activity of the leg extensors was measured before and after the loading as well as 24 and 48 hrs after the loading. The concentrations of the hormones measured increased significantly (p < .01-.001) after both loadings in both groups. The responses tended to be higher in FR than the MR loading and the increases of testosterone concentrations were significantly (p < .01) greater in both loadings in SA than in NA. Both loading protocols in both groups also led to neuromuscular fatigue observable with significant acute decreases in isometric strength by 32-52% (p < .001) and in maximal iEMG (p < .05-01) associated with large increases in blood lactate. These data suggest that, at least in experienced strength athletes, the forced-repetition protocol is a viable alternative to the more traditional maximum-repetition protocol and may even be a superior approach.