Abstract des Autors

Numerous studies have shown that males can generate a higher absolute muscle force, but are less fatigue resistant comparing to females. Even thought aging is accompanied by substantial reductions in muscle mass and strength, it is known, that older adults can sustain a relative submaximal force for a longer duration than young adults. However, findings of quadriceps muscle fatigue after maximal isomeric contractions (MVC) are not well understood, because motor fatigue is task specific and depends of sex, age and the muscle group tested. Thus the aim of our study was to assess gender differences of fatigue from sustained maximal-effort isometric contraction of the knee extensors in older adults. Twenty four young (18–29 years) and twenty older (65–75 years) males and females volunteered to participate in experimental trial. Before experimental procedures anthropometric variables of the subjects were measured (TBF-300 body composition scale „Tanita“ (West Drayton, UK). Subsequently, baseline measures were done: the maximal voluntary contraction (MVC) of knee extensor muscles was measured using an isokinetic dynamometer (System 3; Biodex Medical Systems, Shirley, NY, USA), then involuntary torques were superimposed with electrostimulation of 20Hz and 100Hz stimuli (MG 440; Medicor, Budapest, Hungary). After baseline measures sustained maximum-effort fatiguing contraction of 30 s was conducted. The PTT100 stimulus was superimposed also on the 30-s contraction to asses central activation ratio (CAR). After 5 and 10 min recovery of involuntary (20Hz,100Hz) and voluntary force (MVC) was assessed. Results of our study revealed that baseline involuntary torque, MVC and CAR values of young subjects were greater than older adults (p < 0.05). Moreover, males developed higher MVC and CAR values than females of the same age (p < 0.05). During 30 s fatiguing contractions MVC decreased in all groups (p < 0.05), However, sex-differences of MVC remained only between young adult groups (p < 0.05). MVC recovered up to baseline level after 10 min in all groups ( p < 0.05). During fatiguing contractions CAR values did not changed significantly only in old Lina Kreivėnaitė Lietuvos sporto universitetas Sporto g. 6, LT-44221 Kaunas Mob. +370 619 62454 El. paštas: lina.biathlon@gmail.com Gauta 2016-07-04 Patvirtinta 2016-09-07 females group. CAR of young adults recovered to the baseline level after 5min (p < 0.05), but for older males CAR values reached baseline level only after 10 min. Peripheral fatigue of young man was greater than other groups after fatiguing contraction (p < 0.05). There were age-induced differences in peripheral fatigue, but sex-impact to involuntary torques was not observed. Involuntary torques of 20 and 100 Hz stimuli (P20 and P100) decreased during contraction and increase during recovery (p > 0.05). P20 variables of older adults did not changed, but P100 torque values decreased significantly in all groups during fatiguing contraction (p > 0.05). Significant age interaction established in all groups, but sex interaction imposed only in young adult’s baseline measurements (p < 0.05). P100 values of all subjects fully recovered already in R5 (p > 0.05), and here was no sex impact observed. Main findings of our study are that older females were more fatigue resistant than older males and young adult groups, whereas MVC decreased in all groups, but the greatest decline established in young adult groups. Moreover, central activation ratio of older females was lower than other groups and recovery of CAR was the slowest in older men group. There was an age-induced peripheral fatigue difference, when young had greater peripheral fatigue then older, and young males suffered greatest peripheral fatigue between all of the groups.