Effects of training at simulated altitude on performance and muscle metabolic capacity in competitive road cyclists

Differences between the effects of training at sea level and at simulated altitude on performance and muscle structural and biochemical properties were investigated in 8 competitive cyclists who trained for 3-4 weeks, 4-5 sessions/week, each session consisting of cycling for 60-90 min continuously and 45-60 min intermittently. Four subjects, the altitude group (AG), trained in a hypobaric chamber (574 torr = 2300 m above sea level), and the other four at sea level (SLG). Before and after training work capacity was tested both at simulated altitude (574 torr) and at sea level, by an incremental cycle ergometer test until exhaustion. Work capacity was expressed as total amount of work performed. Venous blood samples were taken during the tests. Leg muscle biopsies were taken at rest before and after the training period. AG exhibited an increase of 33% in both sea level and altitude performance, while SLG increased 22% at sea level and 14% at altitude. Blood lactate concentration at a given submaximal load at altitude was significantly more reduced by training in AG than SLG. Muscle phosphofructokinase (PFK) activity decreased with training in AG but increased in SLG. All AG subjects showed increases in capillary density. In conclusion, work capacity at altitude was increased more by training at altitude than at sea level. Work capacity at sea level was at least as much improved by altitude as by sea level training. The improved work capacity by training at altitude was paralleled by decreased exercise blood lactate concentration, increased capillarization and decreased glycolytic capacity in leg muscle.     

Strength training for 1h in humans: effect on the motor performance of normal upper extremities

It has been found that one session of intense muscle strength training decreases muscle strength temporarily and causes neuromuscular fatigue in the trained muscles, but little attention has been given to the effects of neuromuscular fatigue on the other components of motor performance. The purpose of this study was to examine in normal healthy volunteers the effects of a 1-h strength training session on the motor performance of the upper extremity, including reaction time, speed of movement, tapping speed and coordination. Group of 30 healthy female volunteers, aged 29-47 years, were randomly divided into sub-groups, (A and B, n = 15 per group). Both groups first completed a set of motor performance tests on 3 consecutive days. On the 4th day, group A carried out a 1-h muscle strength training session of the upper extremities. Isometric muscle strengths and electromyogram (EMG) data were recorded before the training session. Immediately after the training session the same recordings were repeated, and additional motor performance tests were also performed. Group B carried out only the motor performance tests. The groups exchanged programmes the following week. The 1-h strength training session decreased the isometric muscle strength of wrist flexion by 18% (P < 0.001) and extension by 18% (P < 0.001) in group A, while in group B flexion strength decreased by 19% (P < 0.001) and extension strength by 17% (P < 0.001). All the measured EMG activations also decreased in both groups. There were no statistically significant differences in the results of the motor performance tests between the mean values of the three baseline measurements and the values recorded after the training session. The result was surprising, but straightforward; neuromuscular fatigue induced by a 1-h strength training session of the upper extremities had no effect on the motor performance functions of the hand, as indicated by reaction times, speed of movement, tapping speed and coordination, in these normal healthy female volunteers.     

Role of agonist and antagonist muscle strength in performance of rapid movements

Six subjects performed rapid self-terminated elbow movements under different mechanical conditions prior to, and 5 weeks after an elbow extensor strengthening programme. Despite the large difference in the strengths of elbow flexors and extensors, the pretest did not demonstrate significant differences between the movement time of flexion and extension movements performed under the same mechanical conditions. The results obtained in the posttest demonstrated a decrease in movement time (i.e. an increase in movement speed) in both elbow flexion and extension movements under some mechanical conditions. In addition, flexion movements demonstrated a relative increase in the acceleration time (acceleration time as a proportion of the movement time). It was concluded that the strength of both the agonist and antagonist muscles was important for the performance of rapid movements. Stronger agonists could increase the acceleration of the limb being moved, while stronger antagonists could facilitate the arrest of the limb movement in a shorter time, providing a longer time for acceleration.     

表面肌电信号的肌肉疲劳判别研究进展

肌肉在周期的收缩或静态的拉伸过程中,会渐渐进入疲劳状态,肌肉疲劳特性的研究在康复医学、运动医学领域具有重要作用。表面肌电信号是从肌肉表面通过电极记录下来的反映神经肌肉系统活动的一维时间序列非平稳生物电信号,是评价局部肌肉疲劳的有效工具。本研究从时域和频域、时频域线性方法下的测量指标和非线性方法下的指标来综述表面肌电信号的疲劳研究进展,同时比较各种方法的优缺点,并对使用表面肌电信号来判别疲劳研究做了进一步的展望。     

Effects of low salinity on antioxidant enzymes activities in kidney and muscle of juvenile silver pomfret Pampus argenteus

Silver pomfret (Pampus argenteus) is an important fish species in China, whose fatality is strongly affected by marine salinity. To better understand the tolerance of sliver pomfret to varying environmental salinity at its early developmental stages, the influence of salinity on the activities of five antioxidant enzymes – superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione-S-transferase (GST), and glutathione reductase (GR) – in the kidney and muscle of juvenile silver pomfret was investigated in this study. Divided groups A, B, C, D at random, the juvenile silver pomfrets were then treated with different salinity levels of 25, 20, 15, and 10 with time periods of 24, 48, 96, and 120 h respectively. Generally speaking, the results show that the renal and muscular SOD as well as the renal CAT activities first rise then drop (P < 0.05), while the muscular CAT activity increases with the elapse of treatment time (P < 0.05) and peaked at 96 h, then decreased at 120 h, while the muscular CAT activity in group D increased consistently and peaked at 120 h. The renal GPX activity decreases significantly (P < 0.05) as the salinity drops and treatment time prolongs with its lowest level occurring at 96 h in group D, while the muscular GPX activity increases first then decrease (P < 0.05); moreover the renal and muscular GPX activities vary reversely in compensation. On a whole, the renal and muscular GST and GR activities first rise then drop (P < 0.05) with the drop of salinity and elapse of time. To sum up, the results acquired from study indicate that the salinity decrease could effectively stimulate and enhance the antioxidant enzyme activity in the kidney and muscle of the juvenile silver pomfrets, thus effectively eliminating the excessive reactive oxygen species (ROS) and minimizing the body damage. Characterized by certain sequentiality and tissue specificity, the activation of the antioxidant enzymes could also be inhibited when the salinity varies beyond the tolerance range of the body.     

Effect of lowered muscle temperature on the physiological response to exercise in men

The effect of low muscle temperature on the response to dynamic exercise was studied in six healthy men who performed 42 min of exercise on a cycle ergometer at an intensity of 70% of their maximal O2 uptake. Experiments were performed under control conditions, i.e. from rest at room temperature, and following 45 min standing with legs immersed in a water bath at 12 degrees C. The water bath reduced quadriceps muscle temperature (at 3 cm depth) from 36.4 (SD 0.5) degrees C to 30.5 (SD 1.7) degrees C. Following cooling, exercise heart rate was initially lower, the mean difference ranged from 13 (SD 4) beats.min-1 after 6 min of exercise, to 4 (SD 2) beats.min-1 after 24 min of exercise. Steady-state oxygen uptake was consistently higher (0.2 l.min-1). However, no difference could be discerned in the kinetics of oxygen uptake at the onset of exercise. During exercise after cooling a significantly higher peak value was found for the blood lactate concentration compared to that under control conditions. The peak values were both reached after approximately 9 min of exercise. After 42 min of exercise the blood lactate concentrations did not differ significantly, indicating a faster rate of removal during exercise after cooling. We interpreted these observations as reflecting a relatively higher level of muscle hypoxia at the onset of exercise as a consequence of a cold-induced vasoconstriction. The elevated steady-state oxygen uptake may in part have been accounted for by the energetic costs of removal of the extra lactate released into the blood consequent upon initial tissue hypoxia.     

Immediate effect of patellar kinesiology tape application on quadriceps peak moment following muscle fatigue: A randomized controlled study

Objective:To investigate the immediate effect of horseshoe taping for patellar superior and inferior gliding (HTPSG and HTPIG, respectively) using kinesiology tape on the peak moment of fatigued quadriceps.Methods:Twenty-eight adults were divided into the HTPSG (experimental) and HTPIG (control) groups. The peak moment of the dominant quadriceps of the participants was measured using Biodex System 4 prior to the experiment and after inducing quadriceps fatigue. The peak moment of the quadriceps was measured after separate application of HTPSG and HTPIG using kinesiology tape.Results:After kinesiology tape application, the peak moment of the quadriceps muscle was significantly increased in both groups (p<.05); however, the peak moment of the fatigued quadriceps muscle was significantly higher in the HTPSG group than in the HTPIG group (p<.05).Conclusions:The application of HTPSG using kinesiology tape would more be helpful for immediate recovery after exercise-induced quadriceps fatigue.     

Effect of growth on efficiency and fatigue in extensor digitorum longus muscle of the rat

The effect of growth on work output, energy consumption and efficiency during repetitive dynamic contractions was determined using extensor digitorum longus muscles of 40-, 60-, 120- and 700-day-old male Wistar rats. When work output of each contraction was normalized to the work output of the first contraction it was found that work output initially increased over the first 10–20 contractions by approximately 8% in each age group. Thereafter a faster decrease in work output was found in the youngest group (approximately 2% each contraction) compared to the older groups (approximately 0.7% each contraction). After 40 contractions the reduction in work output was significantly different only between the youngest group and the two oldest groups (–30% vs –5%). These differences in fatigue were not associated with differences in adenosine 5-triphosphate and phosphocreatine concentrations or in lactate production. Total work output and high-energy phosphate consumption increased by approximately 555% and 380% from age 40 to 120 days, respectively. Consequently, efficiency was significantly higher (approximately 32%) in the older groups compared to 40-day-old animals. Normalized for muscle mass, mean rate of high-energy phosphate consumption was similar in all groups whereas mean power output was significantly lower in the youngest group (approximately 46%). Thus, the difference in efficiency between the young and the other groups may be attributed to a lower external power production in the youngest group rather than changes in energy turnover.     

Interindividual variation of isolated muscle performance and fibre-type composition in the toad<Emphasis Type="Italic"> Bufo viridus</Emphasis>

Interindividual analyses of physiological performance represent one of the most powerful tools for identifying functional positive and negative linkages between various performance traits. In this study we investigated functional linkages in the whole-gastrocnemius performance of juvenile Bufo viridis by examining interindividual variation in in vitro muscle performance and muscle fibre-type composition. We used the work-loop technique to investigate the maximum in vitro power output and fatigue resistance of the gastrocnemius muscle during repeated sets of three cycles at the cycle frequency of 5 Hz, simulating an intermittent style of locomotion. We found several significant correlations between different measures of in vitro muscle performance, including a negative correlation between maximum net power output and fatigue resistance of power, indicating functional trade-offs between these performance traits. We also investigated the extent of individual variation in the proportions of different fibre types, and tested for correlations between individual variation in muscle fibre-type composition and the previously measured isolated muscle performance. Fast glycolytic fibres represented 84.0±3.4% of the muscle, while the combined slow oxidative and fast oxidative-glycolytic fibres represented 16±3.4%. We found no significant correlations between measures of in vitro muscle performance and the proportion of different fibre types in the gastrocnemius muscle. However, despite this lack of correlation between whole-muscle performance and muscle fibre-type composition data, we suggest the functional linkages detected between different measures of in vitro muscular performance have important ecological and evolutionary consequences.Communicated by I.D. Hume     

Effects of heavy barbell hip thrust vs back squat on subsequent sprint performance in rugby players

The objective of this research was to compare the effect of Post-Activation Performance Enhancement (PAPE) exerted on the back squat (BS) versus the barbell hip thrust (HT) on the sprint performance (5- and 10-m). 17 male amateur rugby players participated in the study (age 22.14 ± 2.52 years; body mass 81.06 ± 9.6 kg; height 1.78 ± 0.05 m). All participants performed a dynamic maximum strength test (3RM) in BS and HT at maximum speed. Two randomized sessions were performed inducing PAPE using BS or HT trough three series with three repetitions at 85% 1RM eight minutes before the sprint tests. An ANOVA of repeated measurement, found no differences in the time for 5-m (F = 0.398, P = 0.537, η²p = 0.024) or 10-m (F = 2.589, P = 0.127, η²p = 0.139). There were no significant differences in the Protocol effect between HT and BS in 5-m or 10-m (F = 2.963, P = 0.104, η²p = 0.156 and F = 1.472, P = 0.243 η²p = 0.084, respectively). There were also no differences in the Time x Protocol interaction at 5-m (F = 0.001, P = 0.976, η²p < 0.001) or 10-m (F = 4.174, P = 0.058, η²p = 0.207). The effect size obtained in the results of the sprint tests was small in both exercises (ES < 0.2). None of the BS or HT exercises performed with heavy load induced a significant PAPE phenomenon on the ability to sprint in rugby players.     

The relationship between internal and external loads as a tool to monitor physical fitness status of team sport athletes: a systematic review

The efficiency index (Eff_index) combines internal and external loads, and it has been considered a promising tool to evaluate physical fitness status. However, its real applicability and limitations have not been elucidated yet. To examine and discuss the findings from studies that used Eff_index as a tool for the evaluation of physical fitness status in team sports. A systematic search was performed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). The databases conferred were PubMed, Scopus, Web of Science, SPORTDiscus, MEDLINE and CINAHL. The articles selected were published up to March 2021. Fourteen articles were included after meeting the inclusion criteria. A wide variety of combinations of external and internal loading parameters to calculate Eff_index were found. The pooled sample included 349 male participants (23 ± 3 years). Fifty-nine percent of the sample were soccer players, 20% rugby players, 10% Australian football players, 7% hurling players, and 4% basketball players. Most Eff_index calculations used total distance (TD) divided by heart rate derived parameters. However, recent studies have suggested the use of accelerations as the external load parameter. Eff_index is a simple and powerful tool for the evaluation of physical fitness status in team sports athletes. The disparity of external and internal loading parameters used to calculate Eff_index may affect its sensitivity to detect changes in fitness status in different team sport settings. More studies with indoor team sports and female athletes are warranted.     

Effects of low salinity on antioxidant enzymes activities in kidney and muscle of juvenile silver pomfret Pampus argenteus

Silver pomfret (Pampus argenteus) is an important fish species in China, whose fatality is strongly affected by marine salinity. To better understand the tolerance of sliver pomfret to varying environmental salinity at its early developmental stages, the influence of salinity on the activities of five antioxidant enzymes – superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione-S-transferase (GST), and glutathione reductase (GR) – in the kidney and muscle of juvenile silver pomfret was investigated in this study. Divided groups A, B, C, D at random, the juvenile silver pomfrets were then treated with different salinity levels of 25, 20, 15, and 10 with time periods of 24, 48, 96, and 120 h respectively. Generally speaking, the results show that the renal and muscular SOD as well as the renal CAT activities first rise then drop (P < 0.05), while the muscular CAT activity increases with the elapse of treatment time (P < 0.05) and peaked at 96 h, then decreased at 120 h, while the muscular CAT activity in group D increased consistently and peaked at 120 h. The renal GPX activity decreases significantly (P < 0.05) as the salinity drops and treatment time prolongs with its lowest level occurring at 96 h in group D, while the muscular GPX activity increases first then decrease (P < 0.05); moreover the renal and muscular GPX activities vary reversely in compensation. On a whole, the renal and muscular GST and GR activities first rise then drop (P < 0.05) with the drop of salinity and elapse of time. To sum up, the results acquired from study indicate that the salinity decrease could effectively stimulate and enhance the antioxidant enzyme activity in the kidney and muscle of the juvenile silver pomfrets, thus effectively eliminating the excessive reactive oxygen species (ROS) and minimizing the body damage. Characterized by certain sequentiality and tissue specificity, the activation of the antioxidant enzymes could also be inhibited when the salinity varies beyond the tolerance range of the body.     

Effects of temperature on electromyogram and muscle function

The effects of 30 min of cooling (15 degrees C water) and warming (40 degrees C water) on arm muscle function were measured. A reference condition (24 degrees C air) was included. Of nine young male subjects the maximal grip force (Fmax), the time to reach 66% of Fmax (rate of force buildup) and the maximal rhythmic grip frequency were determined, together with surface electromyographic activity (EMG) of a forearm muscle (flexor digitorum superficialis). The results showed that in contrast to warming, cooling resulted in a significant decrease of 20% in the Fmax and a significant 50% decrease in force build-up time and the maximal rhythmic grip frequency. The relationship between the root mean square value (rms) of the EMG and the static grip force did not change due to temperature changes. The median power frequency (MPF) in the power spectrum of the EMG signal decreased by 50% due to cooling but remained unchanged with heating. During a sustained contraction at 15% of Fmax (Fmax depending on the temperature) the increase in the rms value with contraction time was 90% larger in the warm condition and 80% smaller in the cold condition compared to the increase in the reference condition. The MPF value remained constant during the warm and reference conditions but in the cold it started at a 50% lower value and increased with contraction time.(ABSTRACT TRUNCATED AT 250 WORDS)     

Spatial distribution of active muscle fibre characteristics in the upper trapezius muscle and its dependency on contraction level and duration

The aim of this study was to provide direct in vivo information of the physiological and structural characteristics of active muscle fibres from a large part of the upper trapezius muscle. Two-dimensional (2-D) multi-channel surface electromyography recordings were used, with 13 × 10 electrodes covering 6 × 4.5 cm of the skin’s surface. A previously developed method was applied to detect individual propagating motor unit action potentials and to estimate their corresponding muscle fibre conduction velocity (MFCV) and muscle fibre orientation (MFO). Using these estimates, spatial distributions of MFCV and MFO were examined for five male subjects performing isometric shoulder elevation at different force levels. The main results were: (1) the general relationship between MFCV and force generation was non-systematic, with a positive relationship at the inferior part of the muscle, (2) the spatial distribution of MFCV at different force levels and fatigue was inhomogeneous and (3) the MFO was slightly different (6°) of the muscle fibres with origin superior compared to inferior to the C7 vertebra. These findings provide new information of the MFO of contracting muscle fibres and knowledge of the physiological characteristics of a large part of the upper trapezius muscle that previously was based on observations from human cadavers only.     

Physiological factors in stretcher carriage performance

In this study we examined the anthropometric and physiological factors that may account for the ability to carry a casualty on a stretcher. Eleven young soldiers were pretested to obtain their anthropometry, body composition, physical fitness, and muscle cross-sectional areas. They then performed a two-person manual carry of a stretcher containing an 82-kg manikin while walking on a treadmill at a speed of 4.8 km/h. Subjects walked until volitional fatigue, as indicated by slippage of the stretcher from their hands. Average (SD) carriage time was 2.7(1.4) min with a range of 1.4-6.4 min. A stepwise multiple linear regression revealed that forearm bone-plus-muscle cross-sectional area, thigh muscle cross-sectional area, and push-up performance accounted for most of the variance in hand carriage time (r2 = 0.99, P < 0.001). These data suggest that muscle cross-sectional area and upper-body muscular endurance are important physiological factors in the ability to carry a loaded stretcher by hand.     

Merged plantarflexor muscle activity is predictive of poor walking performance in post-stroke hemiparetic subjects

Stroke is the leading cause of long-term disability and individuals post-stroke often experience impaired walking ability. The plantarflexor (PF) muscles are critical to walking through their contributions to the ground reaction forces and body segment energetics. Previous studies have shown muscle activity during walking can be grouped into co-excited muscle sets, or modules. Improper co-activation, or merging of modules, is a common impairment in individuals post-stroke. The purpose of this study was to determine the influence of merged PF modules on walking performance in individuals post stroke by examining balance control, body support and propulsion, and walking symmetry. Muscle modules were identified using non-negative matrix factorization to classify subjects as having an independent or merged PF module. The merged group had decreased balance control with a significantly higher frontal plane whole-body angular momentum than both the independent and control groups, while the independent and control groups were not significantly different. The merged group also had higher paretic braking and nonparetic propulsion than both the independent and control groups. These results remained when comparisons were limited to subjects who had the same number of modules, indicating this was not a general effect due to subjects with merged PF having fewer modules. It is likely that a merged PF module is indicative of general PF dysfunction even when some activation occurs at the appropriate time. These results suggest an independent PF module is critical to walking performance, and thus obtaining an independent PF module should be a crucial aim of stroke rehabilitation.     

Enzyme activity of rat tibialis anterior muscle differs between treatment with triamcinolone and prednisolone and nutritional deprivation

The maximal activity of a selection of enzymes involved in muscle carbohydrate handling, citric acid cycle and fatty acyl beta-oxidation were studied after treatment with the fluorinated corticosteroid triamcinolone and compared to a similar treatment of the non-fluorinated corticosteroid prednisolone in an equipotent anti-inflammatory dose. Furthermore, because triamcinolone causes loss of body mass and muscle wasting, the effects of triamcinolone were investigated relative to a control group, with the same loss of body mass, due to nutritional deprivation. The study was performed in male Wistar rats in the following treatment groups: TR, triamcinolone treatment (0.25 mg x kg(-1) x day(-1) for 2 weeks), which resulted in a reduction of body mass (24%); ND, nutritional deprivation (30% of normal daily food intake for 2 weeks) resulting in a similar (24%) decrease of body mass as TR; PR, prednisolone treatment (0.31 mg x kg(-1) x day(-1) for 2 weeks), with a 10% increase in body mass; FF, free-fed control group, with a 12% increase in body mass in 2 weeks. Compared to FF, TR induced an increase in phosphofructokinase (PFK) activity (P < 0.01), glycogen synthase [GS(i + d)] activity (P < 0.05) and glycogen content (P < 0.01) in the tibialis anterior muscle. The PR and ND caused no alterations in PFK or citrate synthase (CS) activity compared to FF. Compared to PR, TR induced an increase in PFK (P < 0.01), CS (P < 0.05) and GS(i + d) activity (P < 0.01). Both TR and PR caused an increased muscle glycogen content, being more pronounced in TR (P < 0.05). Compared to ND, TR induced an increased CS (P < 0.05) and GS(i + d) activity (P < 0.01) and glycogen content (P < 0.01). The ND resulted in a decreased glycogen content compared to FF (P < 0.05). None of the treatments affected the activity of glycogen phosphorylase, beta-hydroxyacyl coenzyme A dehydrogenase and lactate dehydrogenase. It was concluded that corticosteroids led to an increased muscle glycogen content; however, the changes in the enzymes of carbohydrate metabolism were corticosteroid type specific and did not relate to undernutrition, which accompanied the triamcinolone treatment.     

Caffeine mouth rinse enhances performance,fatigue tolerance and reduces muscle activity during moderate-intensity cycling

We investigated the effects of caffeine mouth rinse on endurance performance, muscle recruitment (i.e., electromyographic activity of the vastus lateralis and rectus femoris), rating of perceived effort and heart rate. Twelve physically-active healthy men cycled at 80% of their respiratory compensation point until task failure. The participants rinsed their mouths for 10 seconds with placebo (PLA, 25 mL of a solution composed of non-caloric mint essence) or caffeine (CAF, 25 mL of 1.2% of anhydrous caffeine concentration with non-caloric mint essence) every 15 minutes of exercise. Time until exhaustion increased 17% (effect size = 0.70) in CAF compared to PLA (p = 0.04). The wavebands of low-frequency electromyographic activity (EMG) of the vastus lateralis and rectus femoris was lower in CAF group than PLA at 50% of the time until exhaustion (p = 0.04). The global EMG signal was lower in CAF group than PLA at 100% of the time until exhaustion (p = 0.001). The rating of perceived effort pooled was higher in CAF mouth rinse (p = 0.001) than PLA group. No effect was found on the heart rate between the groups (p > 0.05). Caffeine mouth rinse increases endurance performance, rating of perceived effort and decreases muscle activity during a moderate-intensity exercise.     

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 (EMG_rms) 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 EMG_rms 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. Accepted: 5 November 1997     

Parvalbumins distribution and physical state inside the muscle cell

Single skinned muscle fibres (frog) have been submitted to double Ouchterlony immunodiffusion assays with antibodies directed against the two species of frog parvalbumin. The antigenic material which diffuses out of each fibre contains the two parvalbumins. Their presence in each cell is thus demonstrated. The amount of parvalbumins having diffused out of the fibre has been quantified. It corresponds to the parvalbumin content of the cell. This implies that these proteins are freely soluble in the muscle sarcoplasm.