Kynurenine aminotransferase isoforms display fiber-type specific expression in young and old human skeletal muscle.

Conversion of kynurenine (KYN) to kynurenic acid (KYNA) is the main pathway for free tryptophan degradation in skeletal muscle and has emerged as an important mechanism of how exercise is linked to promotion of mental health. Metabolism of KYN to KYNA mainly depends on the expression of kynurenine aminotransferases (KATs) that is under control of the mitochondria biogenesis regulator PGC-1α. We therefore hypothesized that expression of KATs would vary between muscle fibers that differ in mitochondrial content, i.e. oxidative type I vs more glycolytic type II muscle fibers. Moreover, we tested the hypothesis that KAT expression differs with age. Single muscle fibers were isolated from biopsies taken from the vastus lateralis muscle in young and old healthy subjects. In young and old subjects the abundance of KAT I, KAT III and KAT IV was greater in Type I than Type II fibers without age-dependent difference in the KAT isoform expressions. The link to mitochondrial content was further seen as the expression of KAT IV correlated to mitochondrial cytochrome c oxidase IV (COX IV) abundance in both fiber types. In conclusion, we describe for the first time the expression pattern of KAT isoforms with respect to specific fiber types and age in human skeletal muscle.

Shoulder muscle function in frozen shoulder syndrome patients following manipulation under anesthesia: a 6-month follow-up study.

INTRODUCTION: The present study evaluates changes in shoulder muscle function in patients with frozen shoulder syndrome (FSS) following manipulation under general anesthesia (MUA). PATIENTS AND METHODS: Fifteen FSS patients with mean (±SD) age of 53.6±9.7 years were included in this study. Isometric endurance of the shoulder muscles was characterized by time and net impulse (NI), which were assessed with the patient holding a weight in the hand until exhaustion. Fatigability of the deltoid and trapezius muscles during isometric endurance test was assessed by electromyogram power spectrum median frequency (MF) slope per minute. Patients were also screened for daytime pain. Data were collected before MUA, and at 1 and 6 months postoperatively. RESULTS: Six months postoperatively, the MF slope for the trapezius and deltoid muscles of the involved and uninvolved shoulders did not differ (P>0.05), whereas NI remained lower and endurance time was longer (P<0.05). Shoulder pain was reduced as compared to preoperative levels (on visual analog scale) 1 and 6 months postoperatively (P<0.05). DISCUSSION: In patients with FSS, the fastest improvements in shoulder muscle NI, fatigability and pain take place in the first month after MUA; 6 months after MUA, however, NI and endurance time remained impaired for the involved shoulder. Physiotherapy should pay more attention to muscle function recovery. LEVEL OF EVIDENCE: Level III, prospective follow-up study.

Low back muscle fatigue during Sørensen endurance test in patients with chronic low back pain: relationship between electromyographic spectral compression and anthropometric characteristics.

This study assessed low back muscle fatigue during Sørensen back endurance test in chronic low back pain (CLBP) patients and healthy controls, and investigated relationship between the erector spinae muscle fatigability and subject's anthropometric characteristics. Four groups (n = 10 per group) of middle-aged (47-52-year-old) subjects participated: 1) female CLBP patients, 2) healthy female subjects, 3) male CLBP patients and 4) healthy male subjects. Subjects performed Sørensen back endurance test until exhaustion, while electromyographic (EMG) power spectrum median frequency compression over time (MF slope) as indicator of the erector spinae muscle fatigability, and endurance time were recorded. The endurance time was shorter (p < 0.05) in male CLBP patients compared to the healthy male and female subjects. No significant gender differences in endurance time were found in CLBP patients and in healthy subjects. EMG power spectrum MF slope did not differ significantly in CLBP patients and in healthy subjects. However, MF slope was higher (p < 0.05) in healthy male than in female subjects. Body mass and BMI correlated moderately positively with MF slope (r = 0.40-0.67) in all measured groups. We conclude that male CLBP patients had lower back extensor muscle isometric endurance compared to the healthy subjects of both genders, whereas no gender differences in isometric endurance were found in CLBP patients and in healthy subjects. Healthy male subjects had greater lumbar erector spinae muscle fatigability compared to the healthy female subjects. Subjects with higher body mass and body mass index fatigued faster during Sørensen back endurance test.

Changes in soleus motoneuron pool reflex excitability and surface EMG parameters during fatiguing low- vs. high-intensity isometric contractions.

The fatigue-related changes in soleus motoneuron pool reflex excitability and surface electromyography (EMG) parameters, and maximal voluntary contraction (MVC) force of the plantarflexor (PF) muscles during repeatedly sustained low- (30% MVC) vs. high-intensity (70% MVC) isometric contractions were evaluated Twelve young men with mean (+/- SE) age of 22.4 +/- 0.3 years participated in two fatigue tasks on separate days with at least 1-week interval. The fatigue task consisted of three sustained isometric contractions of PF muscles at a target force level until exhaustion separated with 2-min pause between contractions. M-wave (muscle compound action potential) amplitude (M(max)), Hoffmann reflex maximal amplitude (H(max)) to M-wave amplitude ratio (H(max)/M(max)), and root mean square amplitude (RMS) and median frequency (MF) of EMG power spectrum were recorded from the soleus muscle. The M(max) remained constant immediately post-fatigue and during recovery for low- and high-intensity fatigue tasks, whereas H(max)/M(max) was significantly (p < 0.05) reduced only after high-intensity fatigue task. The increase in RMS and decrease in MF during isometric contractions, and reduction in MVC force immediately after the exercise was greater (p < 0.05) for low-intensity fatigue task. We conclude that low-intensity isometric contractions, repeatedly sustained to fatigue, resulted in a marked increase in the EMG amplitude and spectral compression without a significant post-fatigue reflex inhibition of soleus motoneuron pool. High-intensity contractions, however, resulted in post-fatigue reflex inhibition of soleus motoneuron pool and less pronounced EMG spectral compression during fatiguing contractions. A failure of neuromuscular transmission-propagation was not evident after repetitive fatiguing isometric contractions.

Shoulder muscle strength and fatigability in patients with frozen shoulder syndrome: the effect of 4-week individualized rehabilitation.

The effect of 4-week individualized rehabilitation on shoulder muscle strength and fatigability was evaluated in 10 patients with frozen shoulder syndrome (FSS) in comparison of 10 age- and gender-matched healthy control subjects. Isometric maximal voluntary contraction (MVC) force of the shoulder flexors was measured by hand-held dynamometer. Isometric endurance of the shoulder muscles was characterized by endurance time and net impulse (NI) assessed during weight (30% MVC) holding in hand until exhaustion. Fatigability of deltoideus, infraspinatus and trapezius muscles during isometric endurance test was assessed by electromyogram (EMG) power spectrum median frequency (MF) slope per minute. Rehabilitation in patients with FSS consisted of exercise therapy in swimming pool and gymnasium, electrical therapy and massage. Before rehabilitation, patients with FSS had less (p < 0.05) isometric MVC force and NI during endurance test compared to the control. MF slope in patients with FSS for involved extremity was higher (p <0.05) for the deltoideus muscle and less for the infraspinatus muscle before rehabilitation compared to the controls. Shoulder pain was decreased (p < 0.05) and isometric MVC force and NI in endurance test in patients for involved extremity were increased after rehabilitation. No significant changes in endurance time and MF slope for infraspinatus and trapezius muscles in patients for involved extremity were observed after rehabilitation, whereas MF slope for deltoideus muscle was increased. It was concluded that in patients with FSS, 4-week rehabilitation decreased shoulder pain and improved MVC force of the shoulder flexors and isometric working capacity of these muscles during endurance test.

Improvement in Parkinson's disease patients achieved by coordination dynamics therapy.

Eight patients in whom Parkinson's disease had set on 5 to 10 years earlier underwent low intensity coordination dynamics therapy with on average 4 hours per week for 2.5 months. The ongoing pharmaco-therapy and the conventional fitness training for 1 to 2 hours per week were not changed. With the coordination dynamics therapy the functioning of the central nervous system (CNS) of the Parkinson's disease patients improved by 35%, as quantified by coordination dynamics measurements. Following 3 months of no coordination dynamics therapy, but further ongoing pharmaco-therapy and fitness training the CNS functioning worsened again by 21%. It is concluded that pharmaco-therapy and conventional fitness training alone cannot prevent the worsening of the CNS functioning in progressing Parkinson's disease, but additional coordination dynamics therapy can.

Age differences in growth and physical abilities in trained and untrained girls 10-17 years of age.

The purpose of the present study was to assess the age differences in growth characteristics and physical abilities of physically active adolescent girls and to compare them to corresponding data for girls nonactive in sport. The cross-sectional study was carried out on 643 Estonian girls, 10-17 years of age, who were regularly training track and field, and 902 nonactive girls. The organized physical activity of the studied girls consisted of lessons in the school curriculum (2 x 45 minutes per week) for both groups and special track and field training for the first group. Height, weight, and the body mass index (BMI) were used to characterize growth status. Physical ability was assessed with the 30-m dash, standing long jump, medicine ball throw (2 kg), standing quintuplet jump, isometric strength of back extensor muscles, and 1-minute ergocycling at the highest possible rate. Girls active in track and field were taller in all the age groups (P < 0.05-0.001) and lighter except at 17 years, when they were heavier (P > 0.05), but the differences at 12 and 13 years were not significant. BMI was also significantly lower in active girls (P < 0.05-0.001) in all age groups, except at 17 (P > 0.05). The actively training girls had higher physical abilities at all ages from 10-17. The annual differences in performance scores were significant (P < 0.05-0.001) up to 15 years except for the standing long jump. Differences in mean scores of most motor abilities were minimal or reduced significantly at 13-14 years in nonactive girls, but were significant in active girls.

Age-related differences in knee extension rate of isometric force development and vertical jumping performance in women.

AIM: The purpose of this study was to compare knee extension rate of isometric force development and vertical jumping performance characteristics in young, middle-aged and elderly women. METHODS: Unilateral knee extension maximal rate of isometric force development (RFD) was measured by a dynamometer. Maximal squat (SJ) and counter-movement jumps (CMJ) were performed on a force platform. Twelve young (21- to 24-year-old), 12 middle-aged (50- to 58-year-old) and 13 elderly (70- to 76-year-old) women participated. RESULTS: Young women had greater (p<0.05) maximal isometric RFD as compared to older groups. No significant differences in maximal isometric RFD between middle-aged and elderly women have been found. The jumping height in SJ and CMJ was greater in young women as compared to older groups, and in middle-aged women greater as compared to elderly women. Absolute and body mass-related values of CMJ height was greater as compared to SJ height only in young women. Young women had greater jumping height relative to body mass in SJ and CMJ than the other groups. CONCLUSION: The ability to develop isometric force of the knee extensor muscles rapidly did not differ significantly in middle-aged and elderly women. Middle-aged and elderly women had a reduced ability to use the potentiating effect of stretch-shortening cycle to vertical jumping performance during CMJ.

Coordination dynamics in Parkinson's disease patients and healthy subjects quantified by the coordination dynamics recording method and sEMG.

Coordination dynamics were measured in Parkinson's disease patients to quantify central nervous system (CNS) dysfunction. The low-load coordination dynamics in the patients were impaired by 56% for forward and 44% for backward moving in comparison to a control group of similar age. Exercising at higher load was only partly possible. When the disease preferentially affected one side of the body, the coordination dynamics were worse for the affected side. A dexterity test showed that coordination of hand and arm movements could be improved in the short-term memory when exercising on the special coordination dynamics recording and therapy device. Simultaneously taken surface EMG (sEMG) showed that the motor pattern was impaired in the Parkinson's disease patients. sEMG recordings showed further that the fast fatigable muscle fibre activation was impaired. FF-type muscle fibres were already activated for low load in one and not at all in another muscle. In conclusion, coordination between motoneuron firings and between arm and leg movements were found to be impaired in Parkinson's disease patients.

Effects of creatine supplementation during recovery from rapid body mass reduction on metabolism and muscle performance capacity in well-trained wrestlers.

BACKGROUND: The aim of the study was to test the hypothesis that creatine supplementation with concomitant carbohydrate ingestion during recovery period after rapid body mass reduction accelerates the restoration of body mass and physical performance in well-trained wrestlers. METHODS: A double-blind, placebo-controlled cross-over study was conducted on five young healthy male wrestlers, who reduced their body mass by 4.5-5.3% in two series of investigations separated by one month. During 17 hrs recovery period they consumed controlled diet supplemented in random order with glucose (GL trial) or with glucose plus creatine (GL+CR trial). The capacity of the subjects to perform submaximal and maximal (W(max)) intensity work was measured using 5 min intermittent intensity test exercise at the Cybex II device before (Test 1) and after body mass loss (Test 2), also after the recovery (Test 3) on both trials. RESULTS: There was no effect of treatment on the extent of body mass regain during 17 hrs recovery. A significant increase (19.2%) in W(max) from Test 2 to Test 3 was observed in GL+CR trial whereas no change was evident with GL treatment. A strong correlation (r=0.92) was established between the whole body creatine retention and the extent of change in W(max) from Test 2 to Test 3. CONCLUSIONS: The results suggest that creatine supplementation with concomitant glucose ingestion during 17 hrs recovery from rapid body mass loss does not accelerate the restoration of body mass but still stimulates the regain of physical performance in maximal intensity efforts in well-trained wrestlers.

Back extensor muscle fatigability in chronic low back pain patients and controls: Relationship between electromyogram power spectrum changes and body mass index.

Back extensor muscle fatigability and its relationship to body mass index (BMI) was measured in 12 chronic nonspecific low back pain (CNLBP) patients (7 women and 5 men) and 12 healthy age-and gender-matched controls. Subjects performed Sørensen back isometric endurance test until exhaustion while EMG spectral mean power frequency (MPF) over the lumbar erector spinae muscle and endurance time were recorded. The CNLBP patients had significantly shorter endurance time than healthy controls. Spectral MPF significantly declined as time of isometric contraction progressed. Relative decrease of the MPF per minute (MPF slope) for left and right side, and pooled MPF slope was significantly higher in CNLBP patients compared with controls. In CNLBP patients the isometric endurance time correlated significantly negatively with BMI (r=-0.71). In controls BMI correlated significantly positively with MPF slopes of left (r=0.68) and right (r=0.57) side, and pooled MPF slope (r=0.62).

Knee extension strength and vertical jumping performance in nordic combined athletes.

BACKGROUND: The purpose of this study was to measure knee extension strength and vertical jumping performance characteristics in nordic combined athletes. METHODS: Unilateral knee extension isometric maximal force (MF) and rate of force development (RFD) were measured by a special dynamometer, and unilateral isokinetic peak torque (PT) at angular velocities of 60 and 180 deg/sec by a Cybex II dynamometer. Maximal squat (SJ) and counter-movement jumps (CMJ) were performed on force platform. Nine nordic combined athletes as the experimental group and 12 untrained male university students as the control group participated. RESULTS: Nordic combined athletes had a greater (p<0.05) absolute and relative (body mass-related) values of knee extension isometric MF and isokinetic PT, isometric RFD as well as jumping height in SJ and CMJ, than controls. The jumping height in CMJ was greater (p<0.05) compared with SJ only in nordic combined athletes. Jumping height in SJ and CMJ correlated significantly (p<0.05) with knee extension isometric RFD (r=0.62-0.83) and isokinetic PT at angular velocity of 60 deg/sec (r=0.70-0.82) in nordic combined athletes and untrained men. No significant correlation was obtained between unilateral knee extension isometric MF and isokinetic PT or vertical jumping height. CONCLUSIONS: The present study demonstrated a markedly higher voluntary maximal and explosive force-generating capacity of the extensor muscles of lower extremities in nordic combined athletes compared with untrained men, which indicates the adaptation to specific explosive type of strength training.

Isokinetic torque deficit of the knee extensor muscles after arthroscopic partial meniscectomy.

Isokinetic torque deficit of the knee extensor muscles in the operated leg was measured in 21 male patients (mean age 26.4 +/- 1.9 years) who had undergone arthroscopic partial medial meniscectomy. The isokinetic torque testing was performed 1, 3, and 6 months postoperatively using the Cybex II dynamometer according to standard technique. Isokinetic knee extension peak torque (PT) at angular velocities of 60 degrees and 180 degrees/s was determined in both legs, and the proportional PT deficit in the operated leg was compared with that in the nonoperated leg. A significant (P<0.001) isokinetic PT deficit in the operated leg in testing with angular velocity of 60 degrees and 80 degrees/s was observed at 1 month (28.6% and 31.0%, respectively) and 3 months (19.8% and 15.8%, respectively) postoperatively. At 6 months postoperatively a significant (P<0.001) isokinetic PT deficit (18.2%) of the knee extensor muscles in the operated leg was observed only in testing with angular velocity of 60 degrees/s; no significant differences (P>0.05) in isokinetic PT between the operated and nonoperated leg in testing with angular velocity of 180 degrees/s was found 6 months postoperatively. Thus in patients with arthroscopic partial meniscectomy the postoperative recovery of isokinetic strength of the knee extensor muscles in the injured leg is closely related to testing velocity, while it is more delayed at low than intermediate angular velocities.

Age-related differences in twitch contractile properties of plantarflexor muscles in women.

This study compared maximal voluntary isometric strength and electrically evoked twitch characteristics of the plantarflexor muscles among the groups of women of the 3rd (n=14), 4th (n=13), 5th (n=11), 6th (n=12) and 8th (n=13) decade. A significant decrease (P < 0.05-0.001) has been found in isometric maximal voluntary contraction (MVC) force from the 5th decade and in twitch maximal force from the 6th decade. The 3rd decade group produced 72% greater MVC force and 43% greater twitch maximal force than the 8th decade group (P < 0.001). A prolongation (P < 0.01) in twitch contraction time was observed from the 5th decade. Twitch contraction time in the 3rd decade group was 16% shorter (P < 0.001) compared with the 8th decade group (P < 0.01). Twitch half-relaxation time did not differ significantly (P > 0.05) among the groups. A decrease (P < 0. 05-0.001) has been found in twitch maximal rate of force development from the 5th decade and in twitch maximal rate of relaxation from the 6th decade. The 3rd decade group produced 63% greater (P < 0. 001) twitch maximal rate of force development than the 8th decade group. It was concluded that in women a marked age-related reduction in maximal voluntary force-generating capacity of the plantarflexor muscles and speed of contraction of the electrically evoked twitch takes place after 40 years of age, while reduction in maximal force-generating capacity and speed of relaxation of the twitch occurs after 50 years of age.

Twitch contraction properties of plantar flexor muscles in pre- and post-pubertal boys and men.

This study compared electrically evoked twitch contraction characteristics of the plantar flexor muscles in pre-pubertal (11-year-old) and post-pubertal (16-year old) boys, and young (19- to 23-year-old) men. The posterior tibial nerve was stimulated by supramaximal square-wave pulses of 1 ms duration at rest and after brief (5 s) isometric maximal voluntary contraction (MVC) of the plantar flexor muscles, i.e. during postactivation potentiation. Men had higher MVC force than boys and post-pubertal boys higher than prepubertal boys. Pre-pubertal boys had lower peak twitch forces (P(t)) at rest and when potentiated compared with post-pubertal boys and men, whereas no significant differences were found between post-pubertal boys and men. Pre-pubertal boys had higher ratios of P(t) at rest and potentiated P(t) to MVC force than post-pubertal boys and men. No age-related differences were obtained in post-activation potentiation, rest and potentiated twitch contraction and half-relaxation time, and MVC force relative to body mass. The main findings of the study were that puberty is characterized by increased muscle force-generating capacity with no change in twitch potentiation and time-course characteristics, and that twitch force-generating capacity develops in an adult-like pattern after puberty.

Motor performance status in 10 to 17-year-old Estonian girls.

The improvement of motor abilities is associated with the periodical acceleration of changes in adolescents of both sexes. The present cross-sectional study is aimed at establishing smooth curves of motor performance status in 10 to 17-year-old girls. Motor performance was tested in 902 girls with the aid of 30 m dash, standing long jump, vertical jump, pushing a stuffed ball (2 kg), standing quintuplet jump, isometric strength of back extensor muscles, trunk forward flexion and 1-min ergocycling at the highest possible rate. Statistically significant differences of all studied motor abilities between the age groups of 10-12 were indicated. In height and body mass the most pronounced differences (on average 6.5 cm and 7.7 kg, respectively) appeared between the age groups of 12 and 13. At the age of 13 the group results were statistically higher than those at 12 in pushing a stuffed ball, vertical jump, quintuplet jump, strength of back extensors muscle, 30 m dash and ergocycling test, but not in standing long jump and trunk forward flexion. At the age of 14 the performance was not higher than at 13, except in the vertical jump and quintuplet jump. From 14 to 16 years of age differences reappeared in the results of vertical jump, quintuplet jump, pushing a stuffed ball, 1-min cycling and trunk forward flexion but not in the 30 m dash and standing long jump. The lack of significant differences between the age groups of 16 and 17 indicated the final stabilization of tested motor abilities. The obtained results suggest the existence of several periods in motor performance status in 10 to 17-year-old Estonian girls: 1) The biggest differences in the mean results of the tests on motor abilities occurred between ages 10-11, 11-12 and 12-13, which coincide with the biggest differences in height and weight at the same age. 2) The differences in the mean results of most tests on motor abilities stabilized between the age groups of 13 and 14. The mean results of 14-year-old girls were lower in some tests compared to the results of 13-year-olds. 3) The positive differences in the mean results remained between the age groups of 14-15 and 15-16 (excluding the sprint velocity and standing long jump). 4) The final stabilization of motor abilities occurred at the age of 16 to 17.

Neuromuscular fatigue during repeated exhaustive submaximal static contractions of knee extensor muscles in endurance-trained, power-trained and untrained men.

The neural and muscular changes during fatigue produced in repeated submaximal static contractions of knee extensors were measured. Three groups of differently adapted male subjects (power-trained, endurance-trained and untrained, 15 in each) performed the exercise that consisted of 10 trials of submaximal static contractions at the level of 40% of maximal voluntary contraction (MVC) force till exhaustion with the inter-trial rest intervals of 1 min. MVC force, reaction time and patellar reflex time components before and after the fatiguing exercise and following 5, 10 and 15 min of recovery were recorded. Endurance-trained athletes had a significantly longer holding times for all the 10 trials compared with power-trained athletes and untrained subjects. However, no significant differences in static endurance between power-trained athletes and untrained subjects were noted. The fatigue test significantly prolonged the time between onset of electrical and mechanical activity (electromechanical delay) in voluntary and reflex contractions. The electromechanical delay in voluntary contraction condition for power-trained and untrained subjects and in reflex condition for endurance-trained subjects had not recovered 15 min after cessation of exercise. No significant changes in the central component of visual reaction time (premotor time of MVC) and latency of patellar reflex were noted after fatiguing static exercise. It is concluded, that in this type of exercise the fatigue development may be largely owing to muscle contractile failure.

Twitch contractile properties of plantar flexor muscles in power and endurance trained athletes.

This study compared twitch contractile properties of plantar flexor muscles among three groups of 12 subjects each: endurance and power trained athletes and untrained subjects. The posterior tibial nerve was stimulated by supramaximal square wave pulses of 1-ms duration. Power trained athletes had higher twitch maximal force, maximal rates of force development and relaxation and also maximal voluntary contraction (MVC) force. The trained subjects had a smaller twitch maximal force: MVC force ratio and shorter twitch contraction and half-relaxation times than the untrained subjects with no significant differences between the two groups. Thus, the short time for evoked twitches in the athletes compared to the untrained subjects would seem unrelated to the type of training. It is concluded that power training induces a more evident increase of muscle force-generating capacity and speed of contraction and relaxation than endurance training.

Impaction bone-grafting increases the holding power of cancellous screws in the femoral head. A pull-out study in human cadaver hips.

We studied the effect of impaction of fresh cancellous bone or demineralized bone matrix (DBM) around cancellous screws in 25 cadaver femoral heads. The bone mineral content (BMC) of femoral heads was measured to determine if greater relative increase in holding power will be achieved by impaction-grafting, as the BMC of the specimen decreases. A 60% (p < 0.001) relative increase in the pull-out force was achieved by impaction-grafting with DBM, compared to non-grafted controls. The augmenting effect of fresh cancellous bone graft and DBM did not differ significantly. The relative improvement in holding power was not inversely correlated to femoral head BMC, but was inversely related to the pull-out resistance of non-grafted control screws. These findings suggest that impaction-grafting provides significantly better hold of cancellous screws in femoral heads.

Effect of creatine supplementation during rapid body mass reduction on metabolism and isokinetic muscle performance capacity.

Well-trained subjects (n = 6) were studied before and after losing a mean 3.0%-4.3% of body mass to determine whether muscle performance could be maintained or even enhanced by dietary creatine supplementation. During a 5-day period of loss of mass the subjects were randomly assigned to a creatine or placebo supplemented diet. All the subjects were measured before and after loss of mass on both supplements for isokinetic peak torque (PT) and work at peak torque (W(PT)) of knee extensors, also for intermittent high intensity working capacity of the same muscle group. The latter test consisted of submaximal isokinetic knee extensions at an angular velocity of 1.57 rad x s(-1) for 45 s at the rate of 30 contractions each min (submaximal work, Ws max) followed by 15-s maximal effort (maximal work, Wmax). Total duration of the test was 3 min. Haematocrit was measured and haemoglobin, ammonia, lactate, glucose and urea concentrations were analysed in blood samples obtained at rest and after cessation of muscle performance tests. The results indicated that creatine supplementation in comparison with placebo treatment during rapid body mass reduction may help to maintain muscle PT and W(PT)1 at high angular velocities, not influencing Wmax and the rate of fatigue development during Wmax, but affecting adversely Ws max. Within the limitations of the present study the reasons for the partially detrimental effect of creatine administration remain obscure, but it is suggested that impaired creatine uptake in muscle during body mass loss as well as creatine induced changes in muscle glucose and glycogen metabolism may be involved.