ABSTRACT
Introducción: El entrenamiento de fuerza unilateral ha demostrado provocar aumentos de fuerza tanto en la extremidad entrenada como en la no entrenada. Una de las teorías actuales más aceptadas defiende que el origen de dicho aumento de rendimiento se encuentra en adaptaciones en el sistema nervioso, concretamente en la corteza motora primaria, siendo los aumentos en la excitabilidad corticoespinal (EC) medida con estimulación magnética transcraneal una de las principales adaptaciones observadas tras periodos crónicos de entrenamiento. Por ello, el principal objetivo es hacer un análisis de la literatura actual para determinar el grado de adaptación que se da en la EC y su posible relación funcional con el aumento de fuerza de la extremidad no entrenada.DesarrolloSe llevó a cabo una búsqueda sistemática en la literatura existente entre enero de 1970 hasta diciembre de 2016 en las bases de datos online Medline (vía PubMed), Ovid, Web of Science y Science Direct con la siguiente estrategia de búsqueda: (Transcranial magnetic stimulation OR excitability) Y (strength training OR resistance training or force) Y (cross transfer OR contralateral limb OR cross education). Finalmente se incluyeron un total de 10 artículos.ConclusionesExiste cierta inconsistencia en los resultados referentes al aumento de la EC. Aunque no se puede descartar que dicha inconsistencia se deba a aspectos metodológicos, los resultados parecen indicar que el aumento de fuerza y el incremento en la EC podrían no estar funcionalmente relacionados. (AU)
Introduction: Unilateral resistance training has been shown to improve muscle strength in both the trained and the untrained limb. One of the most widely accepted theories is that this improved performance is due to nervous system adaptations, specifically in the primary motor cortex. According to this hypothesis, increased corticospinal excitability (CSE), measured with transcranial magnetic stimulation, is one of the main adaptations observed following prolonged periods of training. The principal aim of this review is to determine the degree of adaptation of CSE and its possible functional association with increased strength in the untrained limb.DevelopmentWe performed a systematic literature review of studies published between January 1970 and December 2016, extracted from Medline (via PubMed), Ovid, Web of Science, and Science Direct online databases. The search terms were as follows: (transcranial magnetic stimulation OR excitability) AND (strength training OR resistance training OR force) AND (cross transfer OR contralateral limb OR cross education). A total of 10 articles were found.ConclusionResults regarding increased CSE were inconsistent. Although the possibility that the methodology had a role in this inconsistency cannot be ruled out, the results appear to suggest that there may not be a functional association between increases in muscle strength and in CSE. (AU)
Subject(s)
Humans , Electromyography , Motor Cortex/physiology , Resistance Training , Transcranial Magnetic StimulationABSTRACT
INTRODUCTION: Unilateral resistance training has been shown to improve muscle strength in both the trained and the untrained limb. One of the most widely accepted theories is that this improved performance is due to nervous system adaptations, specifically in the primary motor cortex. According to this hypothesis, increased corticospinal excitability (CSE), measured with transcranial magnetic stimulation, is one of the main adaptations observed following prolonged periods of training. The principal aim of this review is to determine the degree of adaptation of CSE and its possible functional association with increased strength in the untrained limb. DEVELOPMENT: We performed a systematic literature review of studies published between January 1970 and December 2016, extracted from Medline (via PubMed), Ovid, Web of Science, and Science Direct online databases. The search terms were as follows: (transcranial magnetic stimulation OR excitability) AND (strength training OR resistance training OR force) AND (cross transfer OR contralateral limb OR cross education). A total of 10 articles were found. CONCLUSION: Results regarding increased CSE were inconsistent. Although the possibility that the methodology had a role in this inconsistency cannot be ruled out, the results appear to suggest that there may not be a functional association between increases in muscle strength and in CSE.
Subject(s)
Motor Cortex , Resistance Training , Electromyography , Humans , Motor Cortex/physiology , Muscle, Skeletal , Transcranial Magnetic StimulationABSTRACT
OBJECTIVE: The increase in voluntary force of an untrained limb (i.e. Cross-education) after unilateral resistance training (RT) is believed to be a consequence of cortical adaptations. However, studies measuring neurophysiological adaptations with transcranial magnetic stimulation (TMS) found inconsistent results. One unexamined factor contributing to the conflicting data is the variation in the type and intensity of muscle contractions, fatigue, and the strategies of pacing the movement. Therefore, the purpose was to analyse how those unilateral RT variables affect the adaptations in ipsilateral M1 (iM1) and cross-education. METHODS: We performed a systematic literature review, with the following search terms with Boolean conjunctions: "Transcranial magnetic stimulation" AND "Ipsilateral cortex" AND "Resistance training". RESULTS: The 11 acute and 12 chronic studies included partially support the idea of increased cortical excitability and reduced intracortical inhibition in iM1, but the inconsistency between studies was high. CONCLUSIONS: Differences in type and intensity of contraction, fatigue, and strategies of pacing the movement contributed to the inconsistencies. The tentative conclusion is that high intensity eccentric or externally paced contractions are effective to increase iM1 excitability but cross-education can occur in the absence of such changes. Thus, the mechanism of the cross-education examined with TMS remains unclear.
Subject(s)
Cortical Excitability , Motor Cortex/physiology , Muscle Contraction , Resistance Training , Transcranial Magnetic Stimulation , Adaptation, Physiological , Electromyography , Humans , Muscle, Skeletal/physiologyABSTRACT
OBJECTIVES: This study examined the neural adaptations associated with a low-volume Wingate-based High Intensity Interval Training (HIIT). METHODS: Fourteen recreationally trained males were divided into an experimental (HIIT) and a control group to determine whether a short-term (4 weeks) Wingate-based HIIT program could alter the Hoffmann (H-) reflex, volitional (V-) wave and maximum voluntary contraction (MVC) of the plantar-flexor muscles, and the peak power achieved during a Wingate test. RESULTS: Absolute and relative peak power increased in the HIIT group (ABS_Ppeak: +14.7%, P=0.001; and REL_Ppeak: +15.0%, P=0.001), but not in the control group (ABS_Ppeak: P=0.466; and REL_Ppeak: P=0.493). However, no significant changes were found in the MVC (P>0.05 for both groups). There was a significant increase in H-reflex size after HIIT (+24.5%, P=0.004), while it remained unchanged in the control group (P=0.134). No significant changes were observed either in the V-wave or in the Vwave/Mwave ratio (P>0.05 for both groups). CONCLUSION: The Wingate-based training led to an increased peak power together with a higher spinal excitability. However, no changes were found either in the volitional wave or in the MVC, indicating a lack of adaptation in the central motor drive.
