Acute effects of very low-volume high-intensity interval training on muscular fatigue and serum testosterone level vary according to age and training status.

PURPOSE: To compare the acute physiological responses of three different very low-volume cycling sessions (6 × 5 s, 3 × 30 s, and 3 × 60 s) and their dependence on age and training status. METHODS: Subjects were untrained young men (mean ± SD; age 22.3 ± 4.6 years, VO2peak 42.4 ± 5.5 ml/kg/min, n = 10), older untrained men (69.9 ± 6.3 years, 26.5 ± 7.6 ml/kg/min, n = 11), and endurance-trained cyclists (26.4 ± 9.4 years, 55.4 ± 6.6 ml/kg/min, n = 10). Maximal voluntary contraction (MVC) and electrically stimulated knee extension torque, and low-frequency fatigue, as ratio of stimulation torques at 20-100 Hz (P20/100), were measured only 24 h after exercise. Serum testosterone (Te) and blood lactate concentrations were measured only 1 h after exercise. RESULTS: All protocols increased the blood lactate concentration and decreased MVC and P20/100 in young men, but especially young untrained men. In old untrained men, 6 × 5 s decreased P20/100 but not MVC. Te increased after 3 × 30 s and 3 × 60 s in young untrained men and after 3 × 60 s in older untrained men. The increase in Te correlated with responses of blood lactate concentration, MVC, and P20/100 only in old untrained men. CONCLUSIONS: As little as 6 × 5 s all-out cycling induced fatigue in young and old untrained and endurance-trained cyclists. Slightly higher-volume sessions with longer intervals, however, suppressed contractile function more markedly and also transiently increased serum testosterone concentration in untrained men.

Effect of sprint cycling and stretch-shortening cycle exercises on the neuromuscular, immune and stress indicators in young men.

Selection of optimal physical load is essential for desired adaptation including health benefits. We hypothesized that neuromuscular, immune and stress indicators will be higher after energy demanding sprint interval exercise (SIE) than to mechanically demanding stretch-shortening cycle exercise (SSE). The main aim of this study was to assess and compare the kinetics of blood brain-derived neurotrophic factor (BDNF), norepinephrine (NE) and cortisol (as stress indicators) and proinflammatory (IL-6) and anti-inflammatory (IL-10) cytokines within 24 hours after metabolically demanding SIE and after muscle damage inducing SSE. Twenty healthy physically active young men randomly assigned to two equal groups to complete 12 bouts of 5 s stationary cycling sprints every 3 min (SIE) or 200 drop-jumps with 30 s interval between each jump (SSE), respectively. Quadriceps muscle maximal voluntary contraction torque and voluntary activation and soreness were measured and blood samples collected before and 2 min, 1 hour, 12 hours and 24 hours after the SIE and SSE. The BDNF, cortisol, IL-6 and NE levels increased more at 2 min after SIE than SSE (P < 0.05); however, the IL-10 level did not differ between SIE and SSE. BDNF and cortisol levels were decreased at 24 h after both SIE and especially after SSE. The higher was the initial BDNF level, the greater was its decrease at 24 h after both type of exercise. Before exercise BDNF level correlated closely with the change in central fatigue (decrease in voluntary activation) after both SIE and SSE. We thus conclude that both metabolically demanding SIE and muscle damage inflicting SSE induced long-lasting decrease in circulating BDNF which may not promote brain health. The level of circulating BDNF, but not cortisol, IL-6, IL-10 or NE, was associated with changes in central motor fatigue.

Absence of Bilateral Differences in Child Baseball Players with Throwing-related Pain.

The aim of this study was to assess whether side-to-side differences in morphology and function of the upper limbs in 11-12 year-old male baseball players with throwing-related pain (n=14) were more pronounced than that of age-matched healthy untrained subjects (n=16). Baseball players 1) had played baseball≥4.5 h·wk-1 for ≥ 4 years and (2) suffered from moderate-intensity (3-6 points on 10-point questionnaire scale) throwing-related pain in the shoulder or elbow in at least 2 training sessions within the past month. The range of motion (ROM), function and structure of the elbows and shoulders were assessed using goniometry, isokinetic dynamometry and ultrasonography. While the ROM and eccentric external peak torque of internal shoulder rotation were lower, the thickness of the supraspinatus tendon, the ulnar collateral ligament and articular cartilage of the humeral head were larger in baseball players than controls. There were, however, no significant side-to-side differences in any parameter in either group. In conclusion, it is unlikely that side-to-side differences in shoulder and upper limb structure and function contributed to the throwing-related pain in young baseball players, but low shoulder eccentric external peak torque and range of internal rotation may predispose to throwing-related pain.

Single muscle fibre contractile properties differ between body-builders, power athletes and control subjects.

NEW FINDINGS: What is the central question of this study? Do the contractile properties of single muscle fibres differ between body-builders, power athletes and control subjects? What is the main finding and its importance? Peak power normalized for muscle fibre volume in power athletes is higher than in control subjects. Compared with control subjects, maximal isometric tension (normalized for muscle fibre cross-sectional area) is lower in body-builders. Although this difference may be caused in part by an apparent negative effect of hypertrophy, these results indicate that the training history of power athletes may increase muscle fibre quality, whereas body-building may be detrimental. We compared muscle fibre contractile properties of biopsies taken from the vastus lateralis of 12 body-builders (BBs; low- to moderate-intensity high-volume resistance training), six power athletes (PAs; high-intensity, low-volume combined with aerobic training) and 14 control subjects (Cs). Maximal isotonic contractions were performed in single muscle fibres, typed with SDS-PAGE. Fibre cross-sectional area was 67 and 88% (P < 0.01) larger in BBs than in PAs and Cs, respectively, with no significant difference in fibre cross-sectional area between PAs and Cs. Fibres of BBs and PAs developed a higher maximal isometric tension (32 and 50%, respectively, P < 0.01) than those of Cs. The specific tension of BB fibres was 62 and 41% lower than that of PA and C fibres (P < 0.05), respectively. Irrespective of fibre type, the peak power (PP) of PA fibres was 58% higher than that of BB fibres (P < 0.05), whereas BB fibres, despite considerable hypertrophy, had similar PP to the C fibres. This work suggests that high-intensity, low-volume resistance training with aerobic exercise improves PP, while low- to moderate-intensity high-volume resistance training does not affect PP and results in a reduction in specific tension. We postulate that the decrease in specific tension is caused by differences in myofibrillar density and/or post-translational modifications of contractile proteins.

EVALUATION OF BILATERAL ASYMMETRY BETWEEN UPPER LIMB MASSES IN RIGHT-HANDED YOUNG ADULTS OF BOTH SEXES.

The study introduced a novel precise method for measurement and calculation of upper arm mass and to assess the difference between masses of upper limbs on the dominant and non-dominant sides of the body of right-handed participants. Forty healthy untrained male (n = 20; M age = 20.8 yr., SD = 1.2) and female (n = 20; M age = 20.7 yr., SD = 1.3) participants without a history of upper-extremity pathology participated. Kinematic and kinetic data were collected during arm motion. The mass of each arm was calculated. Each participant performed 20 movements with each arm. Most often the dominant arm was more massive than the non-dominant in both sex groups; however, mass was more symmetric for female participants than for male participants. Regression equations related to total body mass were calculated for each arm independently.

Influence of spatial accuracy constraints on reaction time and maximum speed of performance of unilateral movements.

The goal was to study reaction time and maximal velocity of upper limbs of healthy young adults of both sexes during transition from a simple to a more involved task. Performance of dominant and non-dominant arms was recorded. Participants were 43 healthy, right-handed, untrained men (n=22) and women (n=21), 18-22 years old. The simple task required a single jerk-like movement. The involved task required both speed and accuracy where necessity for high speed of performance was emphasized. The effectiveness of transition between tasks was calculated for both reaction time and maximal velocity. No lateral differences were found. Men usually had a shorter reaction time on both tasks and a higher maximal velocity in the simple task. Women were more effective at modifying velocity.

Stretching exercise volume for flexibility enhancement in secondary school children.

AIM: The study aim was to establish the threshold of stretching volume for flexibility enhancement during physical education lessons in secondary school children. METHODS: Subjects were 239 tenth grade children randomly assigned to four groups (boys 107, girls 132, mean age 15.1 ± 0.4). Children involved in after-school sports were not included in the study. Physical education lessons were performed twice a week for 45 minutes in duration. The intervention lasted for five weeks comprising 10 physical education lessons. Flexibility was determined from sit and reach test before and after intervention. Subjects in group 1 performed standard "sit and reach" test of four trials in every physical education lesson; in group 2 received one stretching exercise of four repetitions; group 3 received four stretching exercises of four repetitions; in group 4 no stretching was performed. RESULTS: Flexibility improvement in group 3 were the greatest (21.6%; P<0.05), smaller in group 2 (12.6%, P<0.05) and smallest in 1 group (5.1%, P<0.05), while control group changes were insignificant (1.7%, P>0.05). CONCLUSION: The main finding was that single flexibility test performed twice a week for five weeks was sufficient stimulus to increase range of motion in secondary school children. Stretching exercises provides exceptional prospects to achieve youths' improvement since schoolchildren are very sensitive to flexibility training.

The effect of plyometric training on central and peripheral fatigue in boys.

The aim of this study was to investigate the effect of high-intensity plyometric training (PT) on central and peripheral fatigue during exercise performed at maximal intensity in prepubertal boys. The boys (n=13, age 10.3+/-0.3 years) performed continuous 2-min maximal voluntary contractions (MVC) before and after 16 high-intensity PT sessions (two training sessions per week, 30 jumps in each session, 20 s between jumps). The greatest effect of PT was on excitation-contraction coupling: twitch force increased by 323.2+/-210.8% and the height of a counter-movement jump increased by 36.7+/-11.7%, whereas quadriceps femoris (QF) muscle voluntary activation index, central activation ratio and MVC did not change significantly after PT. The thickness of QF increased by 8.8+/-7.9% after PT. Central fatigue increased significantly by about 15-20% after PT, whereas peripheral fatigue decreased significantly by about 10% during the 2-min MVC. Central fatigue and peripheral fatigue during the 2-min MVC were inversely related before PT, but this relationship disappeared after PT.

Prolonged muscle damage depends on force variability.

Skeletal muscle damage frequently occurs after eccentric exercise, however, the relationship between intraindividual variability of eccentric exercise and skeletal muscle damage is not clear yet. The aim of the study was to test the hypothesis that prolonged decrease in skeletal muscle force depends on intraindividual variability of eccentric exercise. Eleven healthy men were asked to perform knee eccentric extension of 10 series with 12 repetitions (EE) with maximal intensity at 160 degrees/s. The maximal voluntary knee extension isometric torque (MVC) of the quadriceps muscle and isokinetic concentric torque (IT) at 30 degrees/s of knee angles were established before and 2 min, 60 min, 24 h and 14 days after EE. At 24 h and 48 h after EE muscle soreness and creatine kinase activity before and at 48 h after EE were calculated. The intraindividual variability of EE and autocorrelation coefficient of EE were calculated. We observed a significant decrease in MVC and IT after EE. The maximal isokinetic torque shifted to longer muscle length after EE. It was concluded that longer lasting (within 14 days) indirect symptoms of exercise induced muscle damage (decrease in muscle force) are closely related to variability of EE.

The decrease in electrically evoked force production is delayed by a previous bout of stretch-shortening cycle exercise.

AIM: Unaccustomed physical exercise with a large eccentric component is accompanied by muscle damage and impaired contractile function, especially at low stimulation frequencies. A repeated bout of eccentric exercise results in less damage and improved recovery of contractile function. Here we test the hypotheses that (1) a prior stretch-shortening cycle (SSC) exercise protects against impaired muscle function during a subsequent bout of SSC exercise and (2) the protection during exercise is transient and becomes less effective as the exercise progresses. METHODS: Healthy untrained men (n = 7) performed SSC exercise consisting of 100 maximal drop jumps at 30 s intervals. The same exercise was repeated 4 weeks later. Peak quadriceps muscle force evoked by electrical stimulation at 15 (P15) and 50 (P50) Hz was measured before exercise, after 10, 25, 50 and 100 jumps as well as 1 and 24 h after exercise. RESULTS: P15 and P50 were higher during the initial phase of the repeated bout compared with the first exercise bout, but there was no difference between the bouts at the end of the exercise periods. P15 and P50 were again larger 24 h after the repeated bout. The P15/P50 ratio during exercise was not different between the two bouts, but it was higher after the repeated bout. CONCLUSION: A prior bout of SSC exercise temporarily protects against impaired contractile function during a repeated exercise bout. The protection can again be seen after exercise, but the underlying mechanism then seems to be different.

Behavior of dominant and non dominant hands during ballistic protractive target-directed movements.

The purpose of this study is to investigate the asymmetry of dominant and non-dominant arms regarding reaction time (RT), velocity, force and power generated during ballistic target-directed movements. Fifty six, right-handed young males performed protractile movements with both arms separately by pushing a joystick towards a target-line as quickly and as accurately as possible. Participants performed 21 repetitions with each hand. The temporal, spatial, kinetic and kinematic parameters were computed. All movements were grouped regarding their accuracy (when joystick fell short, stopped precisely or overreached the target). Each group of movements was analyzed separately and the data obtained was compared across groups. The results showed that although the left arm was less accurate than the right one, it reached the target significantly faster, developing greater average force and power. The forces of acceleration and deceleration of the left arm were greater too. We did not observe a significant lateral difference in RT in situations when the arm fell short of the target, or stopped precisely on the target. It was only when the target was overreached that the left arm displayed a significantly greater RT than the right one. We explain the results from the asymmetry of motor behavior in favor of the influence of both hemispheres in this process.

Relationship between simple reaction time and body mass index.

The aim was to establish the relationship between simple reaction time in motor response in young adults in relation to their body physique, as represented by body mass index. Forty-five young male participants were allocated to one of three anthropometric groups, based on their body mass index. Participants performed 100 reaction-time trials with instructions to move a joystick, as quickly as possible, as soon as they detected a single star appearing in the centre of a monitor. All data were statistically selected into seven intervals and data from the mode frequency interval were precisely analysed. Participants from the group with greater body mass index reacted significantly slower than others. We did not record group lateral differences based on simple reaction time in each selected group. We recommend for future researchers the importance of identification of the level of body mass index of participants prior to testing them for effectiveness of simple sensori-motor reactions.

Effect of age on metabolic fatigue and on indirect symptoms of skeletal muscle damage after stretch-shortening exercise.

AIM: The purpose of this study was to establish the main differences between men (M) and adolescents (A) (males) in metabolic fatigue and damage induced by exercise performed at maximal intensity. METHODS: Healthy A (age 13.4 0.6 years, n = 12) and healthy adult M (age 25.4 1.7 years, n = 12) participated in this study. To induce muscle damage and metabolic fatigue stretch-shortening exercise (SSE) (5 bouts of 20 jumps with counter-movement to 90 degrees angle in the knee with 10 s between bouts) has been chosen. The following data were measured: the force of the quadriceps muscle, aroused by electrical stimulation at different frequencies, maximal voluntary contraction force, height of jump (JH), muscle soreness, lactate (La) concentration and creatine kinase (CK) activity in the blood. All the parameters mentioned were measured before exercise and 2-5 min, 20 min, 24 h and 48 h after the SSE, except for La concentration changes in the blood measured before exercise, 2 min and 20 min after the SSE. RESULTS: The main findings in this study are the following: 1) during SSE JH decreased significantly (P < 0.05) more in M than in A, whereas La concentration in the blood after SSE increased more in M than in A; 2) indirect symptoms of muscle damage were more evident in M than in A; 3) there was secondary decrease in electrically induced muscle force at 10-20 Hz from 3 min until 20 min after SSE but only in the muscles of M; 4) low frequency fatigue after SSE was more evident in M than A. CONCLUSIONS: The results of the present study indicate that the muscles of adolescents are more resistant to both metabolic fatigue and exercise-induced damage than those of men.

Skeletal muscle fatigue in long-distance runners, sprinters and untrained men after repeated drop jumps performed at maximal intensity.

One hundred drop jumps were performed at maximal intensity every 20 s in 12 untrained subjects (UT), 9 sprinters (S) and 10 long-distance runners (LDR). Muscle contraction force (P20, P50) induced by percutaneous electrical stimulation (20 Hz and 50 Hz, respectively) as well as maximal voluntary contraction force and the height of vertical jumps performed in different ways decreased (P<0.05) and was not restored to the initial value 20 min post exercise. There was a marked increase in low frequency fatigue (LFF) in all the groups studied as substantiated by a significant decrease in the ratio of P20/P50 immediately after exercise as well as 20 min post exercise compared to pre exercise values (P<0.05). However, low frequency fatigue was similar in UT, S and LDR. The jump height of the sprinters during counter-movement jump and drop jump at 90 degrees decreased to a smaller extent compared to jumps performed by LDR and UT. Muscle pain did not differ between UT, S and LDR at 24 h post exercise. The present data indicate that endurance training status as well as prevalence of muscle fibres of the slow type does not decrease muscle resistance to LFF nor accelerate the recovery of muscle contraction force following maximal, intermittent stretch-shortening cycle exercise.

Changes in height of jump, maximal voluntary contraction force and low-frequency fatigue after 100 intermittent or continuous jumps with maximal intensity.

Healthy untrained males (age 25.4 +/- 1.7 years, n=12) gave their informed consent to take part in all experiments within the study. After 100 intermittent (every 20 s) drop jumps from the height of 0. 4 m, jumps with counter-movement to 90 degrees angle in the knee and immediate maximal rebound (eccentric-concentric exercise; E-C) and 100 continuous jumps (five bouts of 20 jumps with counter-movement to 90 degrees angle in the knee with 10 s between bouts) (maximal exercise; M) with maximal intensity, the height of vertical jump decreased in a similar way, and this decrease did not depend on the performance mode of jumps. After E-C and M jumping exercises, there was a significant (P < 0.001) decrease in maximal voluntary contraction force, as well in the force generated by electrical stimulation at all stimulation frequencies, and these values were not restored to the initial level even after 24 h. After the E-C exercise, however, the muscle contraction force generated at different stimulation frequencies and, especially, at low-stimulation frequencies (1-20 Hz) decreased to a significantly (P < 0.05-0.001) greater extent than after M exercise. Twenty minutes after the end of M exercise, there was still a greater increase in low-frequency fatigue (LFF) and it was no different from the LFF registered 20 min after the end of E-C exercise. Twenty-four hours after the M exercise, however, LFF was smaller than its respective value after E-C exercise. There was no significant relationship between the values of LFF after E-C and M exercises. This may indicate that there are differences in the origin of the LFF after the E-C and M exercises.

Is post-tetanic potentiation, low frequency fatigue (LFF) and pre-contractile depression (PCD) coexistent in intermittent isometric exercises of maximal intensity?

The aim of our experiment was to test the hypothesis that the performance of maximal isometric exercise every 20 s would reduce the intermediate frequency force, i.e. the force that appears while stimulating the muscle at 15 and 20 Hz, and would produce less decrease the force at 10 and 50 Hz, while Pt would increase. Such changes in stimulated force should demonstrate the coexistence of potentiation, low frequency fatigue (LFF) and 'post-contractile depression' (PCD). The quadriceps muscle of 14 healthy men (aged 19-37 years) was studied. The results have shown, that during isometric exercise of maximal intensity there was significant (P < 0.05) decrease in P15 and P20, increase in Pt, however, MVC and P10 and P50 was unchanged (P > 0.05). LFF manifested itself most significantly which is evident from decrease in P20/P50. During recovery after work there was significant increase in LFF and decrease in P50 which is indicative of the manifestation of PCD. Besides, there was significant (P < 0.05) decrease immediately after exercise in RTP20 and RTP50, while no changes in T50 and RT. There were no significant changes (P > 0.05) however, either in RTP20 and RTP50 or in T50 and RT 20 min after exercise if compared to the initial and immediately post-exercise values.

Effects of contraction duration on low-frequency fatigue in voluntary and electrically induced exercise of quadriceps muscle in humans.

The aims of this study were to investigate if low-frequency fatigue (LFF) dependent on the duration of repeated muscle contractions and to compare LFF in voluntary and electrically induced exercise. Male subjects performed three 9-min periods of repeated isometric knee extensions at 40% maximal voluntary contraction with contraction plus relaxation periods of 30 plus 60 s, 15 plus 30 s and 5 plus 10 s in protocols 1, 2 and 3, respectively. The same exercise protocols were repeated using feedback-controlled electrical stimulation at 40% maximal tetanic torque. Before and 15 min after each exercise period, knee extension torque at 1, 7, 10, 15, 20, 50 and 100 Hz was assessed. During voluntary exercise, electromyogram root mean square (EMGrms) of the vastus lateralis muscle was evaluated. The 20-Hz torque:100-Hz torque (20:100 Hz torque) ratio was reduced more after electrically induced than after voluntary exercise (P < 0.05). During electrically induced exercise, the decrease in 20:100 Hz torque ratio was gradually (P < 0.05) reduced as the individual contractions shortened. During voluntary exercise, the decrease in 20:100 Hz torque ratio and the increase in EMGrms were greater in protocol 1 (P < 0.01) than in protocols 2 and 3, which did not differ from each other. In conclusion, our results showed that LFF is dependent on the duration of individual muscle contractions during repetitive isometric exercise and that the electrically induced exercise produced a more pronounced LFF compared to voluntary exercise of submaximal intensity. It is suggested that compensatory recruitment of faster-contracting motor units is an additional factor affecting the severity of LFF during voluntary exercise.

Submaximal-exercise-induced impairment of human muscle to develop and maintain force at low frequencies of electrical stimulation.

The aim of this study was to test the hypothesis that low intensity exercise-induced low frequency fatigue is caused by failure of excitation-contraction coupling. Changes in knee extension torque at 5, 10, 15, 20 and 50 Hz electrical stimulation of quadriceps muscle in ten healthy, young, male subjects were recorded during 20-min voluntary exercise followed by 60-min recovery. In seven of the ten subjects, changes in torque during 3 min of 10-Hz stimulation were recorded 2 min and 20 min after 20 min voluntary exercise. Exercise was performed at 30% of maximal voluntary contraction with a contraction plus relaxation period of 6 plus 4 s. Torque at 5, 10, 15, 20 and 50-Hz stimulation at the end of exercise was reduced to mean 91.0 (SEM 5.4)%, 68.7 (SEM 5.4)%, 67.2 (SEM 3.9)%, 66.5 (SEM 4.5)% and 74.7 (SEM 4.3)% of control values, respectively. During the first 30 s of the 3 min 10-Hz stimulation, torque was reduced in exercised muscle and increased in nonfatigued muscle. The reduction in torque was more marked 20 min after exercise than after 2 min. In conclusion, the pattern of depression and recovery of muscle force observed was in agreement with the hypothesis that the main cause of low intensity exercise-induced low frequency fatigue is an impairment of excitation-contraction coupling.

Complex evaluation of velocity, force, and accuracy characteristics of the movements of upper extremities in young athletes.

8 measures recorded during alternate tapping of two targets by left and right hands for 15 boys, 13 or 14 yr. old, were made during 4 30-sec. trials using a force averaging 450 gm. Mechanical and electrical activity (EMG from m. biceps brachii) of both hands suggested asymmetric characteristics of the two hands and the likely involvement of different types of muscle fibers or asymmetry of the CNS.