Effects of load and fatigue during unilateral resistance training on neuromuscular adaptations.

El entrenamiento de fuerza (EF) unilateral aumenta la fuerza voluntaria máxima tanto del músculo entrenado, como del músculo homologo contralateral no entrenado, un fenómeno conocido como efecto cruzado. El efecto cruzado surge de adaptaciones neurales en el hemisferio no entrenado como consecuencia de su activación concurrente junto con el hemisferio entrenado durante contracciones unilaterales. La magnitud del efecto cruzado se estima en un 12% de la fuerza voluntaria máxima, lo que se podría considerar de baja relevancia clínica. Variables relacionadas con el EF como la intensidad y la fatiga durante la serie influyen sobre la activación concurrente del hemisferio no entrenado durante contracciones unilaterales, por lo que podrían ser manipuladas para aumentar la magnitud del efecto cruzado. Por tanto, el principal objetivo de esta tesis es determinar el efecto de la intensidad de entrenamiento y el nivel de fatiga durante la serie sobre el efecto cruzado y los cambios neurales agudos en los circuitos corticales y corticoespinales que proyectan sobre el miembro entrenado y no entrenado. Se piensa que estos cambios agudos, que ocurren tras una única sesión de EF, podrían ser los detonantes de las adaptaciones neurales sostenidas a largo plazo que dan lugar a los aumentos en la fuerza voluntaria. En el primer estudio, determinamos los efectos de la intensidad del EF en las respuestas agudas del bíceps braquial a la estimulación magnética transcraneal y eléctrica cervicomedular tras una sesión de EF. Encontramos un aumento en la respuesta a ambos tipos de estimulación. Sin embargo, la intensidad de entrenamiento solo afectó a la respuesta a la estimulación magnética transcraneal, observándose mayores aumentos en las respuestas tras EF de alta intensidad. Estos datos sugieren que la intensidad del EF afecta a la excitabilidad cortical. En el segundo estudio, realizamos una revisión sistemática para analizar qué variables del EF podrían afectar a las adaptaciones neurales del hemisferio no entrenado. Encontramos que el EF unilateral aumenta la excitabilidad cortical y disminuye la inhibición intracortical. Sin embargo, se observó una falta de consistencia en los resultados, probablemente debido a la influencia de variables de entrenamiento como el tipo de contracción, la intensidad de entrenamiento, la fatiga o la estrategia para el control del tempo durante el movimiento, las cuales influyen sobre las adaptaciones del hemisferio no entrenado. En el tercer estudio, determinamos el efecto de la intensidad de entrenamiento en la excitabilidad corticoespinal y la eficacia de los circuitos intracorticales del bíceps braquial entrenado y no entrenado tras una sesión de EF. Encontramos un aumento en la excitabilidad corticoespinal del músculo entrenado tras EF de alta intensidad pero no de baja intensidad, sin cambios en la inhibición o facilitación intracortical. Sin embargo, los efectos de una sola sesión de EF fueron específicos del miembro entrenado, pues no se halló ningún cambio en el hemisferio no entrenado independientemente de la intensidad de entrenamiento. En el cuarto estudio, determinamos el efecto de la intensidad de entrenamiento y el grado de fatiga durante la serie en el efecto cruzado y las adaptaciones neurales crónicas derivadas de un periodo de cuatro semanas de EF. Observamos que el entrenamiento de fuerza de alta intensidad, no así el de baja intensidad, mejoró la fuerza voluntaria en los extensores de rodilla entrenados y no entrenados, sin que la fatiga durante la serie influyera en dichas adaptaciones. Además, los aumentos en la fuerza se relacionaron con cambios en la excitabilidad corticoespinal de ambas piernas. Esta tesis muestra que la intensidad de entrenamiento influye en las adaptaciones funcionales derivadas del EF. Sin embargo, a pesar de la influencia de la intensidad de entrenamiento en los cambios agudos en la excitabilidad corticoespinal, la cual sugiere una mayor influencia del EF de alta intensidad sobre estructuras supraespinales, los aumentos crónicos en la fuerza tras un periodo corto de EF no se asocian con cambios en la excitabilidad corticoespinal. La excitabilidad corticoespinal del hemisferio no entrenado no cambió ni tras una sesión ni tras cuatro semanas de EF independientemente de la intensidad de entrenamiento, probablemente debido al menor estímulo que recibe. Además, la fatiga durante el EF, la cual puede aumentar la activación concurrente del hemisferio no entrenado, no tiene ningún efecto aditivo en las adaptaciones del miembro no entrenado y por tanto puede evitarse.Actividad Física y Deport

Training intensity-dependent increases in corticospinal but not intracortical excitability after acute strength training

The purpose of this study was to determine whether the increases in corticospinal excitability (CSE) observed after one session of unilateral isometric strength training (ST) are related to changes in intracortical excitability measured by magnetic brain stimulation (TMS) in the trained and the contralateral untrained biceps brachii (BB) and whether such changes scale with training intensity. On three separate days, 15 healthy young men performed one ST session of 12 sets of eight isometric contractions of the right elbow flexors at 0% (control session), 25%, or 75% of the maximal voluntary contraction (MVC) in a random order. Before and after each session separated at least by 1 week, motor evoked potential (MEP) amplitude, short-interval intracortical inhibition (SICI), contralateral silent period (SP), and intracortical facilitation (ICF) generated by TMS were measured in the trained and the untrained BBs. Compared with baseline, MEPs recorded from the trained BB increased by similar to 47% after training at 75% of MVC (P .05). MEPs in the untrained BB and SICI, SP, and ICF in either BB did not change. Therefore, acute high-intensity but not low-intensity unilateral isometric ST increases CSE in the trained BB without modifications in intracortical inhibition or facilitation. Thus, increases in corticospinal neurons or alpha-alpha-motoneuron excitability could underlie the increases in CSE. Regardless of contraction intensity, acute isometric ST did not modify the excitability of the ipsilateral primary motor cortex measured by TMS

Does Heavy-Resistance Training Improve Mobility and Perception of Quality of Life in Older Women?

[Abstract] Regular physical exercise has shown great benefits in preventing age-related functional losses and in improving the perception of health-related quality of life (HRQoL) in older people. To optimize these benefits, it would be interesting to evaluate what type of exercise is better. Therefore, the purpose of this study was to assess the effects of heavy-resistance training on mobility and HRQoL in older women. Forty healthy, untrained older women (60–75 years) were randomly assigned to three groups: circuit resistance training (CRT, n = 15), traditional resistance training (TRT, n = 15) or the control group (CG, n = 10). During the 12-week training period, both experimental groups performed training with heavy loads, twice a week. Before and after the training period, the Timed Up and Go test, as a proxy of mobility, and the perception of HRQoL were evaluated. TRT and CRT resulted in a statistically significant improvement in the Timed Up and Go test (−5.4 and −10.3%, respectively; p < 0.05), but only the improvement after CRT was significantly greater than changes in the CG (p < 0.001). Only CRT elicited improvements in several dimensions of the perception of the HRQoL questionnaire, such as: physical functioning (13%, p < 0.001), general health (8.1%; p = 0.048), vitality (17.7%; p < 0.001), role emotional (6.7%; p = 0.044) and physical component summary (6.3%; p = 0.001). The change in the CRT group was greater than in the CG (p < 0.001) in the physical functioning score. The present findings show that CRT might be a time- (and hence cost-) effective alternative to trigger multiple positive functional and psychological adaptations in older women.This work was supported by the grants from Fundación San Antonio, reference n: PMAFI-10/21Fundación Universitaria San Antonio (Murcia); PMAFI-10/2

Differences in the effects of a startle stimulus on rate of force development between resistance-trained rock climbers and untrained individuals: Evidence for reticulospinal adaptations?

The aim of the present cross-sectional study was to determine if chronic rock climbing and climbing-specific resistance training (RT) would modify the reticulospinal tract (RST) efficacy. Sixteen healthy, elite level climbers (CL; n = 16, 5 F; 29.8 ± 6.7 years) with 12 ± 7 years of climbing and climbing-specific RT experience and 15 healthy recreationally active participants (CON; n = 15, 4 F; 24.6 ± 5.9 years), volunteered for the study. We quantified RST efficacy by comparing the effects of a startle stimulus over reaction time (Rtime) and measured rate of force development (RFD) and surface electromyography (sEMG) in representative muscles during powerful hand grip contractions. Both groups performed two Rtime tasks while performing rapid, powerful gripping with the right hand (Task 1) or during 3-s-long maximal voluntary right hand grip contractions in response to an imperative visual signal alone (V), or combined with a auditory-non startle stimulus (A) or/and startling auditory stimulus (S). We also tested the reproducibility of these responses on two separate days in CON. Intersession reliability ranged from 0.34 to 0.96 for all variables. The CL versus CON was 37% stronger (p = 0.003). The S stimulus decreased Rtime and increased RFD and sEMG in both groups during both tasks (all p < 0.001). Rtime was similar between groups in all conditions. However, CL had a greater RFD from 50 to 100 ms compared with CON only after the S stimulus in both tasks (p < 0.05, d = 0.85–0.96). The data tentatively suggest that chronic rock climbing and climbing-specific RT might improve RST efficacy, by increasing RST input to the α-motoneurons13 página

Co-existence of peripheral fatigue of the knee extensors and jump potentiation after an incremental running test to exhaustion in endurance trained male runners

[EN] The aim of the present study was to investigate the effect of an incremental running exercise until exhaustion on twitch responses and jump capacity in endurance trained runners. For this purpose, 8 experienced endurance male runners were required to perform neuromuscular function tests before and after a submaximal running bout (control condition -CTR-) or an incremental running test to volitional exhaustion (experimental conditions -EXP-). The twitch interpolation technique was used to assess voluntary activation and muscle contractile properties before and after each condition (CTR and EXP). Countermovement jump was also used to assess the stretch-shortening cycle function before and after both conditions. In addition, rating of perceived exertion, heart rate, blood lactate and skin temperature were also recorded. Only EXP improved jump performance, however, it was also accompanied by a reduction in maximal voluntary contraction and the peak twitch force of the knee extensors evoked by electrical stimulation at 10 Hz (Db10). It is likely that reductions in maximal voluntary contraction may be related to an excitation- contraction coupling failure (i.e. low-frequency fatigue) as suggest the reduction in the Db10. The current results confirm that acute changes in jump performance may not be appropriate to evaluate acute fatigue in endurance trained runner

Training load but not fatigue affects cross-education of maximal voluntary force

The purpose of this study was to determine the effects of training load (25% vs. 75% of one repetition maximum [1RM]) and fatigue (failure vs. non-failure) during four weeks of unilateral knee extension resistance training (RT) on maximal voluntary force in the trained and the untrained knee extensors. Healthy young adults (n = 42) were randomly assigned to control (CON, n = 9, 24 +/- 4.3 years), low-load RT to failure (LLF, n = 11, 21 +/- 1.3 years, three sets to failure at 25% of 1RM), high-load RT to failure (HLF, n = 11, 21 +/- 1.4 years, three sets to failure at 75% of 1RM), and high-load RT without failure (HLNF, n = 11, 22 +/- 1.5 years, six sets of five repetitions at 75% of 1RM) groups. Before and after the four weeks of training, 1RM, maximal voluntary isometric force, and corticospinal excitability (CSE) were measured. 1RM in the trained (20%, d = 0.70, 15%, d = 0.61) and the untrained knee extensors (5%, d = 0.27, 6%, d = 0.26) increased only in the HLF and HLNF groups, respectively. MVIC force increased only in the trained leg of the HLF (5%, d = 0.35) and HLNF groups (12%, d = 0.67). CSE decreased in the VL of both legs in the HLNF group (-19%, d = 0.44) and no changes occurred in the RF. In conclusion, high- but not low-load RT improves maximal voluntary force in the trained and the untrained knee extensors and fatigue did not further enhance these adaptations. Voluntary force improvements were unrelated to CSE changes in both legs

Chronic functional adaptations induced by the application of transcranial direct current stimulation combined with exercise programs: A systematic review of randomized controlled trials

This work was supported by the Spanish Ministry of Science, Innovation, and Universities under Grant (PID2021-128204OA-I00-AEI/FEDER, UE)[Abstract]: The present systematic review aimed to determine the chronic effects of the combination of transcranial direct current stimulation (tDCS) and exercise on motor function and performance outcomes. We performed a systematic literature review in the databases MEDLINE and Web of Science. Only randomized control trials that measured the chronic effect of combining exercise (comprising gross motor tasks) with tDCS during at least five sessions and measured any type of motor function or performance outcome were included. A total of 22 interventions met the inclusion criteria. Only outcomes related to motor function or performance were collected. Studies were divided into three groups: (a) healthy population (n = 4), (b) neurological disorder population (n = 14), and (c) musculoskeletal disorder population (n = 4). The studies exhibited considerable variability in terms of tDCS protocols, exercise programs, and outcome measures. Chronic use of tDCS in combination with strength training does not enhance motor function in healthy adults. In neurological disorders, the results suggest no additive effect if the exercise program includes the movements pretending to be improved (i.e., tested). However, although evidence is scarce, tDCS may enhance exercise-induced adaptations in musculoskeletal conditions characterized by pain as a limiting factor of motor function.Xunta de Galicia, Universidade da Coruna/CISUG ; (ED431B 2021/28

Functional Relevance of Resistance Training-Induced Neuroplasticity in Health and Disease

[Abstract] Repetitive, monotonic, and effortful voluntary muscle contractions performed for just a few weeks, i.e., resistance training, can substantially increase maximal voluntary force in the practiced task and can also increase gross motor performance. The increase in motor performance is often accompanied by neuroplastic adaptations in the central nervous system. While historical data assigned functional relevance to such adaptations induced by resistance training, this claim has not yet been systematically and critically examined in the context of motor performance across the lifespan in health and disease. A review of muscle activation, brain and peripheral nerve stimulation, and imaging data revealed that increases in motor performance and neuroplasticity tend to be uncoupled, making a mechanistic link between neuroplasticity and motor performance inconclusive. We recommend new approaches, including causal mediation analytical and hypothesis-driven models to substantiate the functional relevance of resistance training-induced neuroplasticity in the improvements of gross motor function across the lifespan in health and disease

Effects of load and fatigue during unilateral resistance training on neuromuscular adaptations.

El entrenamiento de fuerza (EF) unilateral aumenta la fuerza voluntaria máxima tanto del músculo entrenado, como del músculo homologo contralateral no entrenado, un fenómeno conocido como efecto cruzado. El efecto cruzado surge de adaptaciones neurales en el hemisferio no entrenado como consecuencia de su activación concurrente junto con el hemisferio entrenado durante contracciones unilaterales. La magnitud del efecto cruzado se estima en un 12% de la fuerza voluntaria máxima, lo que se podría considerar de baja relevancia clínica. Variables relacionadas con el EF como la intensidad y la fatiga durante la serie influyen sobre la activación concurrente del hemisferio no entrenado durante contracciones unilaterales, por lo que podrían ser manipuladas para aumentar la magnitud del efecto cruzado. Por tanto, el principal objetivo de esta tesis es determinar el efecto de la intensidad de entrenamiento y el nivel de fatiga durante la serie sobre el efecto cruzado y los cambios neurales agudos en los circuitos corticales y corticoespinales que proyectan sobre el miembro entrenado y no entrenado. Se piensa que estos cambios agudos, que ocurren tras una única sesión de EF, podrían ser los detonantes de las adaptaciones neurales sostenidas a largo plazo que dan lugar a los aumentos en la fuerza voluntaria. En el primer estudio, determinamos los efectos de la intensidad del EF en las respuestas agudas del bíceps braquial a la estimulación magnética transcraneal y eléctrica cervicomedular tras una sesión de EF. Encontramos un aumento en la respuesta a ambos tipos de estimulación. Sin embargo, la intensidad de entrenamiento solo afectó a la respuesta a la estimulación magnética transcraneal, observándose mayores aumentos en las respuestas tras EF de alta intensidad. Estos datos sugieren que la intensidad del EF afecta a la excitabilidad cortical. En el segundo estudio, realizamos una revisión sistemática para analizar qué variables del EF podrían afectar a las adaptaciones neurales del hemisferio no entrenado. Encontramos que el EF unilateral aumenta la excitabilidad cortical y disminuye la inhibición intracortical. Sin embargo, se observó una falta de consistencia en los resultados, probablemente debido a la influencia de variables de entrenamiento como el tipo de contracción, la intensidad de entrenamiento, la fatiga o la estrategia para el control del tempo durante el movimiento, las cuales influyen sobre las adaptaciones del hemisferio no entrenado. En el tercer estudio, determinamos el efecto de la intensidad de entrenamiento en la excitabilidad corticoespinal y la eficacia de los circuitos intracorticales del bíceps braquial entrenado y no entrenado tras una sesión de EF. Encontramos un aumento en la excitabilidad corticoespinal del músculo entrenado tras EF de alta intensidad pero no de baja intensidad, sin cambios en la inhibición o facilitación intracortical. Sin embargo, los efectos de una sola sesión de EF fueron específicos del miembro entrenado, pues no se halló ningún cambio en el hemisferio no entrenado independientemente de la intensidad de entrenamiento. En el cuarto estudio, determinamos el efecto de la intensidad de entrenamiento y el grado de fatiga durante la serie en el efecto cruzado y las adaptaciones neurales crónicas derivadas de un periodo de cuatro semanas de EF. Observamos que el entrenamiento de fuerza de alta intensidad, no así el de baja intensidad, mejoró la fuerza voluntaria en los extensores de rodilla entrenados y no entrenados, sin que la fatiga durante la serie influyera en dichas adaptaciones. Además, los aumentos en la fuerza se relacionaron con cambios en la excitabilidad corticoespinal de ambas piernas. Esta tesis muestra que la intensidad de entrenamiento influye en las adaptaciones funcionales derivadas del EF. Sin embargo, a pesar de la influencia de la intensidad de entrenamiento en los cambios agudos en la excitabilidad corticoespinal, la cual sugiere una mayor influencia del EF de alta intensidad sobre estructuras supraespinales, los aumentos crónicos en la fuerza tras un periodo corto de EF no se asocian con cambios en la excitabilidad corticoespinal. La excitabilidad corticoespinal del hemisferio no entrenado no cambió ni tras una sesión ni tras cuatro semanas de EF independientemente de la intensidad de entrenamiento, probablemente debido al menor estímulo que recibe. Además, la fatiga durante el EF, la cual puede aumentar la activación concurrente del hemisferio no entrenado, no tiene ningún efecto aditivo en las adaptaciones del miembro no entrenado y por tanto puede evitarse.Actividad Física y Deport

Variability in response to non-invasive brain stimulation protocols" by López-Alonso V, Sandrini M, Colomer-Poveda D.

This chapter focuses on the concept of variability in response to non-invasive brain stimulation (NIBS) techniques, with a particular emphasis on transcranial direct current stimulation (tDCS). It explores both inter-individual and intra-individual variability, analyzing the presence of responders and non-responders to stimulation, as well as the different statistical methods employed to assess this variability. While intra-individual variability appears to be lower than inter-individual variability, it still presents challenges in interpreting NIBS results.Furthermore, the chapter discusses the factors that influence variability in NIBS studies. These factors can be categorized into non-modifiable physiological factors (such as sex, age, genetics and anatomical features), modifiable factors (including medical and non-medical substances), technical factors (e.g., stimulation parameters), and statistical aspects.By identifying the contributing factors and tailoring stimulation protocols to individual needs, researchers can optimize the effectiveness of NIBS interventions. However, due to the complexity and multitude of factors involved, more research is needed to fully elucidate the mechanisms underlying this variability in NIBS.<br/