Vytautas Streckis

Children are more susceptible to central fatigue than adults

Performance in high‐intensity exercise is dependent on the ability to activate motor units. The main aim of this study was to test the hypothesis that adult men and women (age 19–27 years) are able to maintain higher levels of voluntary activation (VA) in knee extensor muscles than boys and girls (age 12–14 years). The volunteers (n = 7 in each group) performed three 5‐s maximal voluntary contractions (MVCs) and a continuous 2‐min MVC. The VA and fatigue of the muscles was assessed by applying 250‐ms 100‐HZ test tetani (TT100HZ). During brief MVCs girls showed lower VA than women, but the difference between boys and men was not significant. During the 2‐min MVC, VA in boys and girls was more depressed than in adults. The end‐exercise values of the relative TT100HZ torque correlated with the average VA during the exercise. Thus, the results of the study support the hypothesis that children are more susceptible to central fatigue than adults. This should be taken into account when evaluating results of fitness tests that require high levels of motor unit activation. Muscle Nerve, 2007

Repeated Bout Effect Was More Expressed in Young Adult Males Than in Elderly Males and Boys

This study investigated possible differences using the same stretch-shortening exercise (SSE) protocol on generally accepted monitoring markers (dependent variables: changes in creatine kinase, muscle soreness, and voluntary and electrically evoked torque) in males across three lifespan stages (childhood versus adulthood versus old age). The protocol consisted of 100 intermittent (30 s interval between jumps) drop jumps to determine the repeated bout effect (RBE) (first and second bouts performed at a 2-week interval). The results showed that indirect symptoms of exercise-induced muscle damage after SSE were more expressed in adult males than in boys and elderly males, suggesting that the muscles of boys and elderly males are more resistant to exercise-induced damage than those of adult males. RBE was more pronounced in adult males than in boys and elderly males, suggesting that the muscles of boys and elderly males are less adaptive to exercise-induced muscle damage than those of adult males.

The effect of multiple sclerosis and gender on central and peripheral fatigue during 2-min MVC

OBJECTIVE The aim of this study was to evaluate the effect of secondary progressive MS disease on central and peripheral fatigue in women and men during continuous 2-min maximal voluntary contractions (MVC) of the quadriceps muscle. METHODS We studied age-matched (40-50-years of age) healthy individuals (men, n=9; women, n=10) and MS patients (men, n=9; women, n=9). The inclusion criteria for MS patients were a Kurtzke Expanded Disability Status Score <4 and a Fatigue Severity Scale Score >5. RESULTS The electrically-induced torque, MVC, and voluntary activation (VA) values were significantly greater in healthy persons than in MS patients. At the end of exercise, the fatigue index of MVC and VA was greater in MS patients than in the healthy cohort, whereas the electrically-induced torque was significantly decreased in healthy individuals. Peripheral fatigue was directly correlated with VA in MS patients; in contrast, it was inversely correlated with VA in healthy men. The variability of torque increased significantly during exercise and did not depend on MS and gender. CONCLUSIONS MS increased central fatigue and diminished peripheral fatigue significantly during 2-min MVC; however, only peripheral fatigue was significantly greater in healthy men than in healthy women. SIGNIFICANCE These results suggest the specified pattern of central and peripheral fatigue in MS patients and could be further exploited for potential therapeutic uses, for instance, to model exercise-induced less central fatigue, and this may not be differentiated between men and women.

Effects of age and sex on fatigability and recovery from a sustained maximal isometric voluntary contraction

The aim was to assess the effects of sex and age on fatigability and recovery from sustained maximal voluntary contraction (MVC) of the knee extensor muscles. The central (central activation ratio (CAR) and electrical activity amplitude) and peripheral (electrically evoked torque and muscle contractile properties) factors contributing to fatigue and recovery of 24 young adults (12 males) aged 23.2±3.6years and 20 older adults (12 males) aged 70.6±4.4years were compared. The increase in central and peripheral fatigue was greater (p⩽0.01) in the young adults vs the older adults. Sex differences (p=0.002) regarding MVC were attributed to the greater (p<0.01) peripheral fatigue of males vs females. The recovery rate of MVC was greater (p<0.001) in the young adults vs the older adults, with no sex effect. The recovery of MVC was correlated with the CAR in older adults (p=0.001). Thus, the greater endurance observed with age is caused by differences in central and peripheral mechanisms, whereas the greater endurance in females is caused by a difference in a mechanism located within the muscle. The impaired recovery from fatigue in older adults relied more on the recovery of central factors.

Interval Running Training Improves Cognitive Flexibility and Aerobic Power of Young Healthy Adults.

Abstract Venckunas, T, Snieckus, A, Trinkunas, E, Baranauskiene, N, Solianik, R, Juodsnukis, A, Streckis, V, and Kamandulis, S. Interval running training improves cognitive flexibility and aerobic power of young healthy adults. J Strength Cond Res 30(8): 2114–2121, 2016—The benefits of regular physical exercise may well extend beyond the reduction of chronic diseases risk and augmentation of working capacity, to many other aspects of human well-being, including improved cognitive functioning. Although the effects of moderate intensity continuous training on cognitive performance are relatively well studied, the benefits of interval training have not been investigated in this respect so far. The aim of the current study was to assess whether 7 weeks of interval running training is effective at improving both aerobic fitness and cognitive performance. For this purpose, 8 young dinghy sailors (6 boys and 2 girls) completed the interval running program with 200 m and 2,000 m running performance, cycling maximal oxygen uptake, and cognitive function was measured before and after the intervention. The control group consisted of healthy age-matched subjects (8 boys and 2 girls) who continued their active lifestyle and were tested in the same way as the experimental group, but did not complete any regular training. In the experimental group, 200 m and 2,000 m running performance and cycling maximal oxygen uptake increased together with improved results on cognitive flexibility tasks. No changes in the results of short-term and working memory tasks were observed in the experimental group, and no changes in any of the measured indices were evident in the controls. In conclusion, 7 weeks of interval running training improved running performance and cycling aerobic power, and were sufficient to improve the ability to adjust behavior to changing demands in young active individuals.

Effect of the time of day on central and peripheral fatigue during 2-min maximal voluntary contractions in persons with multiple sclerosis: gender differences

There is a lack of data on fatigue changes within 24h among patients with multiple sclerosis. The purpose of this study was to evaluate the effect of time of day on central and peripheral fatigue during a continuous 2-min maximal voluntary contraction of the quadriceps muscle in women and men with multiple sclerosis (MS). We studied age-matched MS patients (range, 40-50years). The inclusion criteria for patients were: a Kurtzke Expanded Disability Status score and a Fatigue Severity Scale score. We found a significant gender difference in central activation ratio (CAR) in the evening. At the end of the 2-min maximal voluntary contraction (MVC), the voluntary torque decreased by about 65% in men and women with MS in both the morning and evening. We also observed that, in women, CAR decreased markedly during the first 30s in the evening test. The most interesting finding of our study is that central fatigue increased, whereas peripheral fatigue decreased markedly in the evening only in women. It remains unclear why womens central fatigue is greater in the evening than in the morning.