Muscle Fatigue Is Attenuated When Applying Intermittent Compared With Continuous Blood Flow Restriction During Endurance Cycling.

PURPOSE: The aim of this study was to identify a blood-flow-restriction (BFR) endurance exercise protocol that maximizes metabolic strain and minimizes muscle fatigue. METHODS: Twelve healthy participants accomplished 5 different interval cycling endurance exercises (2-min work, 1-min rest) in a randomized order: (1) control, low intensity with unrestricted blood flow (CON30); (2) low intensity with intermittent BFR (i-BFR30, ∼150 mm Hg); (3) low intensity with continuous BFR (c-BFR, ∼100 mm Hg); (4) unloaded cycling with i-BFR0 (∼150 mm Hg); and (5) high intensity (HI) with unrestricted blood flow. Force production, creatine kinase activity, antioxidant markers, blood pH, and potassium (K+) were measured in a range of 5 minutes before and after each cycling exercise protocol. RESULTS: HI showed the highest reduction (Δ = -0.26 [0.05], d = 5.6) on blood pH. Delta pH for c-BRF30 (Δ = -0.02 [0.03], d = 0.8) and Δ pH for i-BRF30 (Δ = -0.04 [0.03], d = 1.6) were different from each other, and both were higher compared with CON30 (Δ = 0.03 [0.03]). There was significant before-to-after force loss following HI (Δ = 55 [40] N·m-1, d = 1.5) and c-BFR30 (Δ = 27 [21] N·m-1, d = 0.7) protocols only, which were accompanied by significant increases in K+ (HI: Δ = 0.94 [0.65] mmol·L-1, d = 1.8; c-BFR30: Δ = 0.72 [0.85] mmol·L-1, d = 1.2). Moreover, all BFR conditions elicited slight increases in plasma creatine kinase, but not for HI and CON30. Glutathione changes from before to after were significant for all BFR conditions and HI, but not for CON30. CONCLUSIONS: The attenuation in fatigue-induced reductions in maximal force suggests that i-BFR exercise could be preferable to c-BFR in improving exercise capacity, with considerably less biologic stress elicited from HI exercises.

Bilateral muscle strength symmetry and performance are improved following walk training with restricted blood flow in an elite paralympic sprint runner: Case study.

OBJECTIVES: Investigate the influence of 4 weeks of walk training with blood flow restriction (BFR) on muscle strength, metabolic responses, 100-m and 400-m performances in an athlete with cerebral palsy. METHODS: An elite Paralympic sprinter (20 years, 176 cm, 64.8 kg) who presented with moderate hemiplegic cerebral palsy (right side impaired) completed four visits before and after 4 weeks of the BFR training: 1) anthropometric measurements, familiarization of maximal voluntary contraction (MVC), and an incremental test; 2) MVC measurements; 3) 400-m performance, and 4) 100-m performance. The walk training with BFR consisted of four bouts of 5 min at 40% of maximal aerobic speed with 1 min of passive rest with complete reperfusion. RESULTS: All performance times were lower with training (100-m: 1%; 400-m: 10%), accompanied by adaptations in aerobic variables (V˙O2max: 6%; OBLA: 24%) and running economy (9-10%). Lactic acid energy metabolism was reduced (25-27%), even in the presence of a higher lactate efflux from the previously active muscles after training. MVC (right leg: 19%; left leg: 9%) increased in both legs unevenly, decreasing the muscle strength asymmetry between limbs. CONCLUSIONS: These results indicate that cardiovascular and neuromuscular adaptations can be simultaneously induced following BFR training in a paralympic sprinter.

Effects of fast-velocity eccentric resistance training on early and late rate of force development.

This study examined whether short-term maximal resistance training employing fast-velocity eccentric knee extensor actions would induce improvements in maximal isometric torque and rate of force development (RFD) at early (<100 ms) and late phases (>100 ms) of rising torque. Twenty healthy men were assigned to two experimental groups: eccentric resistance training (TG) or control (CG). Participants on the TG trained three days a week for a total of eight weeks. Training consisted of maximal unilateral eccentric knee extensors actions performed at 180 °s-1. Maximal isometric knee extensor torque (MVC) and incremental RFD in successive 50 ms time-windows from the onset contraction were analysed in absolute terms (RFDINC) or when normalised relative to MVC (RFDREL). After eight weeks, TG demonstrated increases in MVC (28%), RFDINC (0-50 ms: 30%; 50-100 ms: 31%) and RFDREL (0-50 ms: 29%; 50-100 ms: 32%). Moreover, no changes in the late phase of incremental RFD were observed in TG. No changes were found in the CG. In summary, we have demonstrated, in active individuals, that a short period of resistance training performed with eccentric fast-velocity isokinetic muscle contractions is able to enhance RFDINC and RFDREL obtained at the early phase of rising joint torque.

Four weeks of blood flow restricted training increases time to exhaustion at severe intensity cycling exercise / Quatro semanas de treinamento com restrição de fluxo sanguineo aumenta o tempo de exaustão em exercício severo no ciclismo

The present study aimed to verify the effects of 4 weeks of low-intensity blood flow restricted (BFR) training on time to exhaustion (Tlim) at severe-intensity exercise. Thirteen physically active subjects (23 ± 3.4 years; 70.6 ± 7.8 kg; 170.9 ± 10 cm) were assigned to one of two groups: low-intensity interval training with (BFR, n=9) or without (CON, n=4) blood flow restricted. The interval training sessions consisted of 2 sets of 5-8 × 2-min intervals at 30% of peak power output (Ppeak) obtained during incremental exercise for LOW and BFR, separated by 1min of rest. For BFR a cuff was inflated (140-200mmHg) during the exercise bouts and deflated during rest intervals. The pressure was increased 20mmHg after three completed sessions, thus, in the last week the pressure applied was 200mmHg. Before and after 4 weeks intervention period, all subjects completed an incremental exercise until exhaustion and one-step transition to a severe-intensity work rate (110%Ppeak). The results revealed that BFR (Pre: 227 ± 44s vs. Post: 338 ± 76s), but not CON (Pre: 236 ± 24s vs. Post: 212 ± 26s), increase significantly Tlim at 110%Ppeak. It can be concluded that 4 weeks of BFR training, but not CON, increased the exercise tolerance at severe intensity domain. Therefore, the increased metabolic and physiologic strains induced by BFR, not the exercise intensity per se (30%Ppeak), seem to have been responsible to trigger the adaptive responses linked to longer Tlim after BFR training.

Este estudo verificou o efeito de quatro semanas de treinamento de baixa intensidade com restrição do fluxo sanguíneo (RFS) no tempo de exaustão (Tlim) realizado em domínio severo. Treze sujeitos fisicamente ativos (23 ± 3,4 anos; 70.6 ± 7.8 kg; 170.9 ± 10 cm) foram divididos em dois grupos: treinamento intervalado com restrição de fluxo (RFS, n=9); e sem restrição (CON, n=4). O treino para ambos os grupos consistiu em 2 x 5-8 repetições de 2min a 30% da potência máxima (Ppeak) obitida durante teste incremental, com intervalos de 1min entre as repetições. Para o RSF o esfigmomamometro foi inflado a uma pressão de 140-200mmHg durante o período de exercício e desinflado nos intervalos. A pressão foi aumentada em 20mmHg a cada três sessões, assim, na última semana a pressão era 200mmHg. Antes e depois das quatro semanas de intervenção, todos os sujeitos realizaram um teste incremental até exaustão voluntária e um teste de carga constante com intensidade de 110%Ppeak. Os resultados mostraram que para o grupo BFR (Pre: 227±44s vs. Pos: 338±76s), mas não para o CON (Pre: 236±24s vs. Pos: 212±26s), o Tlim a 110%Ppeak aumentou significativamente após treinamento. Podemos concluir que 4 semanas de treinamento com BFR aumentou a tolerância ao exercício realizado no domínio severo, sem aumento no grupo CON. Assim, o maior estresse metabólico e fisiológico gerado pela restrição do fluxo sanguíneo, e não a intensidade de exercício per se, parece ter sido responsável pelas respostas adaptativas relacionadas ao aumento do Tlim após o treinamento.

Isokinetic eccentric resistance training prevents loss in mechanical muscle function after running.

The aim of the study was to verify whether 8 weeks of resistance training employing maximal isokinetic eccentric (IERT) knee extensor actions would reduce the acute force loss observed after high-intensity treadmill running exercise. It was hypothesized that specific IERT would induce protective effects against muscle fatigue and ultrastructural damages, preventing or reducing the loss in mechanical muscle function after running. Subjects were tested before and after IERT protocol for maximal isometric, concentric and eccentric isokinetic knee extensor strength (60° and 180° s(-1)). In a second session, subjects performed treadmill running (~35 min) and the previously mentioned measurements were repeated immediately after running. Subsequently, subjects were randomized to training (n = 12) consisting of 24 sessions of maximal IERT knee extensors actions at 180° s(-1), or served as controls (n = 8). The effects of acute running-induced fatigue and training on isokinetic and isometric peak torque, and rate of force development (RFD) were investigated. Before IERT, running-induced eccentric torque loss at 180° s(-1) was -8 %, and RFD loss was -11 %. Longitudinal IERT led to reduced or absent acute running-induced losses in maximal IERT torque at 180° s(-1) (+2 %), being significantly reduced compared to before IERT (p < 0.05), however, RFD loss remained at -11 % (p > 0.05). In conclusion, IERT yields a reduced strength loss after high-intensity running workouts, which may suggest a protective effect against fatigue and/or morphological damages. However, IERT may not avoid reductions in explosive muscle actions. In turn, this may allow more intense training sessions to be performed, facilitating the adaptive response to running training.

Effects of a single habituation session on neuromuscular isokinetic profile at different movement velocities.

Single training session (STS) may increase the power output (i.e., maximal torque) in different contraction types; however, little is known about the neuromuscular adaptations to reach this enhancement. In this way, the present study examined the differences between knee extensors EMG, kinematics, and dynamometry at 60 and 180° s(-1) before (PRE) and after (POST) a STS. Seventeen healthy males completed three different tasks: (1) 5-maximal isokinetic knee extensions, without previous habituation (PRE) at 60 and 180° s(-1); (2) in the same day and after a proper rest, two bouts of 5-maximal isokinetic contractions (STS) at 60 and 180° s(-1); and (3) in a new visit, POST consisted in new 5-maximal isokinetic contractions at 60 and 180° s(-1). The main parameters examined were: knee extensors peak torque (PT), total work (TW), EMG (prior to the movement onset, agonist and antagonist activation), rate of force (RFD), and velocity development (RVD). There was significant increase in PT [12% (60° s(-1)) and 8.7% (180° s(-1))] and TW [13.5% (60° s(-1)) and 10.7% (180° s(-1))] from PRE to POST sessions. Increases in RFD were found for both velocities (p < 0.05); however, RVD and vastus lateralis EMG prior to the movement onset were significantly higher for POST only at 60° s(-1). The RFD percentage of change (%change) was significantly correlated to %change for PT at 60° s(-1) (r(2) = 0.53) and 180° s(-1) (r(2) = 0.45). In conclusion, STS improves neural strategies to contract muscles stronger and faster at the slowest velocity, while higher velocities present different adaptations and might need more practice to further adaptations.

Taxa de desenvolvimento de força em diferentes velocidades de contrações musculares / Rate of force development in different muscle contraction velocities

O objetivo deste estudo foi comparar a taxa de desenvolvimento de força (TDF) nas contrações isométrica e isocinética concêntrica a 60º.s-1 e 180º.s-1. Quatorze indivíduos do gênero masculino (idade = 23,1 ± 2,8 anos; estatura = 174 ± 31,3cm; massa corporal = 81 ± 12kg) realizaram inicialmente uma familiarização ao equipamento isocinético. Posteriormente, os indivíduos realizaram em ordem randômica cinco contrações isocinéticas máximas para os extensores do joelho a 60º.s-1 e 180º.s-1 para determinar o torque máximo concêntrico (TMC) e duas contrações isométricas máximas de 3s para determinar o torque máximo isométrico (TMI). O TMI (301,4 ± 56,0N.m) foi maior do que o TMC a 60º.s-1 (239,8 ± 42,2N.m) e 180º.s-1 (175,0 ± 32,5 N.m). O TMC a 60º.s-1 foi maior do que o TMC a 180º.s-1. Para os intervalos de 0-30ms e 0-50ms, a TDF na condição isométrica (1.196,6 ± 464,6 e 1.326,5 ± 514,2N.m.s-1, respectivamente) foi similar à TDF a 60º.s-1 (1.035,4 ± 446,2 e 1.134,3 ± 448,4N.m.s-1) e maior do que a 180º.s-1 (656,7 ± 246,6 e 475,2 ± 197,9N.m.s-1), sendo ainda que a TDF na contração concêntrica a 180º.s-1 foi menor do que a 60º.s-1. No intervalo de 0-100ms, a TDF da contração isométrica (1.248,8 ± 417,4N.m.s-1) foi maior que a obtida na contração isocinética rápida (909,2 ± 283,4N.m.s-1). A TDF obtida na contração isocinética lenta (1.005,4 ± 247,7N.m.s-1) foi similar à obtida na contração isométrica e na concêntrica isocinética rápida. No intervalo 0-150ms, a TDF isométrica (1.084,2 ± 332,1N.m.s-1) foi maior do que as concêntricas (60º.s-1 e 180º.s-1) (834,8 ± 184,2 e 767,6 ± 201,8N.m.s-1, respectivamente), não existindo diferenças entre estas duas últimas. Conclui-se que a TDF é dependente do tipo e da velocidade de contração, suportando a hipótese de que maiores velocidades de contração acarretam maior inibição do drive neural no início do movimento.

The objective of this study was to compare the maximal rate of force development (RFD) at maximal isometric and isokinetic concentric contractions at 60º.s-1 and 180º.s-1. Fourteen active males (age = 23.1 ± 2.8 years; height = 174 ± 31.3 cm and body mass = 81 ± 12 kg) volunteered to participate in this study. During the first visit, subjects performed a familiarization to the isokinetic equipment. During the second visit, subjects performed in random order 5 maximal isokinetic concentric contractions for knee extensors at each angular velocity (60 and 180º.s-1) to determine maximal concentric torque (MCT) and 2 maximal isometric contractions of 3 s to determine maximal isometric torque (MIT). The MIT (301.4 ± 56.0 N.m) was higher than MCT at 60º.s-1 (239.8 ± 42.2 N.m) and 180º.s-1 (175.0 ± 32.5 N.m). The MCT at 60º.s-1 was higher than MCT at 180º.s-1. At intervals of 0-30ms and 0-50ms, the RFD at isometric contraction (1196.6 ± 464.6 and 1326.5 ± 514.2 N.m.s-1, respectively) was similar to that obtained during concentric contraction at 60º.s-1 (1035.4 ± 446.2 N.m.s-1 and 1134.3 ± 448.4 N.m.s-1, respectively) and higher than that obtained during concentric contraction at 180º.s-1 (656.7 ± 246.6 N.m.s-1 and 475,2±197,9 N.m.s-1, respectively). For the interval of 0-100ms, RFD at isometric contraction (1248.7 ± 417.4 N.m.s-1) was higher than that obtained during concentric contractions at 180º.s-1 (909.2 ± 283.4 N.m.s-1), and similar to concentric contractions at 60º.s-1 (1005.4 ± 247.7 N.m.s-1). However, for the interval of 0-150ms, RFD at isometric contraction (1084.2 ± 332.1 N.m.s-1) was higher than at 60º.s-1 (834.8 ± 184.2 N.m.s-1) and 180º.s-1 (767.6 ± 767.6 N.m.s-1). It can be concluded that RFD is dependant on the contraction type and velocity, supporting the hypothesis that higher speed of contraction generates higher neural drive inhibition at the beginning of the movement.