ABSTRACT
Skeletal muscle force production following repetitive contractions is preferentially reduced when muscle is evaluated with low-frequency stimulation. This selective impairment in force generation is called low-frequency fatigue (LFF) and could be dependent on the contraction type. The purpose of this study was to compare LFF after concentric and eccentric maximal and submaximal contractions of knee extensor muscles. Ten healthy male subjects (age: 23.6 ± 4.2 years; weight: 73.8 ± 7.7 kg; height: 1.79 ± 0.05 m) executed maximal voluntary contractions that were measured before a fatigue test (pre-exercise), immediately after (after-exercise) and after 1 h of recovery (after-recovery). The fatigue test consisted of 60 maximal (100 percent) or submaximal (40 percent) dynamic concentric or eccentric knee extensions at an angular velocity of 60°/s. The isometric torque produced by low- (20 Hz) and high- (100 Hz) frequency stimulation was also measured at these times and the 20:100 Hz ratio was calculated to assess LFF. One-way ANOVA for repeated measures followed by the Newman-Keuls post hoc test was used to determine significant (P < 0.05) differences. LFF was evident after-recovery in all trials except following submaximal eccentric contractions. LFF was not evident after-exercise, regardless of exercise intensity or contraction type. Our results suggest that low-frequency fatigue was evident after submaximal concentric but not submaximal eccentric contractions and was more pronounced after 1-h of recovery.
Subject(s)
Adult , Humans , Male , Young Adult , Muscle Contraction/physiology , Muscle Fatigue/physiology , Muscle, Skeletal/physiology , Analysis of Variance , Electric Stimulation , Electromyography , Exercise Test/methods , Isometric Contraction/physiology , Knee Joint/innervation , Knee Joint/physiology , Young AdultABSTRACT
O conhecimento da inervaçåo macro e micróscopia do joelhoé importante para compreender-se a origem e o mecanismo das gonalgias. Såo descritos os principais ramos dos nervos articulares e os nociceptores, que eståo presentes nas diferentes estruturas anatomicas que compöem o joelho. Ambos såo importantes na gênese dos arcos reflexos sômato-somático e sômato-viscerais, estes reflexos explicam as gonalgias bcom alteraçöes estruturais do membro inferior e com as manifestaçöes viscerais e psíquicas. Os autores relacionam estes conhecimentos neurofisiológicos com a teoria dos canais de energia e dos pontos de acupuntura da medicina tradicional chinesa, evidenciando-se a importância da inervaçåo e dos nociceptores no mecanismo de açåo das agulhas de acupuntura