Role of the Effort Index in Predicting Neuromuscular Fatigue During Resistance Exercises.

Rodríguez-Rosell, D, Yáñez-García, JM, Mora-Custodio, R, Torres-Torrelo, J, Ribas-Serna, J, and González-Badillo, JJ. Role of the effort index in predicting neuromuscular fatigue during resistance exercises. J Strength Cond Res XX(X): 000-000, 2020-This study aimed: (a) to analyze the acute mechanical, metabolic, and electromyographic (EMG) response to 16 resistance exercise protocols (REPs) defined by the first repetition's mean velocity and the percentage of velocity loss (%VL) over the set in the full-squat (SQ) exercise; and (b) to assess whether the effort index (EI, the product of the first repetition's mean velocity and the %VL in the set) could be used as an objective indicator of neuromuscular fatigue. Eleven resistance-trained men performed 16 REPs in the SQ exercise. For the configuration of the 16 REPs, 4 relative intensities (50, 60, 70, and 80% 1 repetition maximum) and 4 magnitudes of %VL (∼10, ∼20, ∼30, and ∼45%) were used. The induced fatigue after each REP was quantified using the percentage of change in (a) countermovement jump (CMJ) height, (b) mean propulsive velocity attained with the load that elicited an ∼1.00 m·s (V1 m·s load), and (c) changes in surface EMG variables. Blood lactate concentration was also collected. The EI presented very strong relationships with the %VL with the V1 m·s load, CMJ height, and post-exercise lactate concentration (r = 0.92, 0.93, and 0.91, respectively; p < 0.001). Moderate to strong relationships were found between the EI and the changes in amplitude (r = 054-0.58; p < 0.05), frequency (r = -0.55 to -0.83; p < 0.05-0.001), and time-frequency (r = 0.52-0.77; p < 0.05-0.001) EMG variables. In addition, the moderate to strong relationships found between the relative changes in mechanical, metabolic, and EMG variables after each REP reinforce the validity of the EI as an objective indicator of muscle fatigue, metabolic stress, and neural effect induced by typical resistance training sessions. Thus, by adjusting the EI in each session, it is possible to quantifying the actual level of effort experienced by each individual during resistance exercises.

Effort Index as a Novel Variable for Monitoring the Level of Effort During Resistance Exercises.

Rodríguez-Rosell, D, Yáñez-García, JM, Torres-Torrelo, J, Mora-Custodio, R, Marques, MC, and González-Badillo, JJ. Effort index as a novel variable for monitoring the level of effort during resistance exercises. J Strength Cond Res 32(8): 2139-2153, 2018-This study aimed to analyze the acute mechanical and metabolic response to resistance exercise protocols (REPs) defined by 2 variables: the first repetition's mean velocity and the percentage of velocity loss (%VL) over the set. The product of these 2 variables was termed the effort index (EI) and was used as an indicator of the degree of fatigue induced during each REP. Twenty-one resistance-trained men (11 in full squat [SQ] and 10 in bench press [BP]) performed 16 REPs separated by 72 hours. Relative loads used (50, 60, 70, and 80% 1-repetition maximum) were determined from the load-velocity relationship for the SQ and BP, whereas volume was objectively determined using the %VL attained over the set (10, 20, 30, and 45% for SQ, and 15, 25, 40, and 55% for BP). Lactate concentration and velocity against the load that elicited a ∼1.00 m·s (V1 m·s load) were measured before and after each REP. Post-exercise velocity with the V1 m·s load and lactate concentration were significantly different (P < 0.01-0.001) from pre-exercise after all REPs. A very close relationship was found between the proposed EI and %VL with the V1 m·s load (r = 0.92-0.98) and post-exercise lactate concentration (r = 0.91-0.95) in both exercises. The correlations between this new index and fatigue indicators such as VL allow us to gain further insight into the actual degree of effort incurred during resistance exercise. In addition to being a valuable addition for training monitoring, the proposed EI could also be used as an independent variable in training studies by equalizing the effort between different interventions.

Effects of Resistance Training and Combined Training Program on Repeated Sprint Ability in Futsal Players.

The purpose of this study was to compare the effects of 6 weeks resistance training (RT) with combined RT and loaded change of direction (CD) exercise on muscle strength and repeated sprint ability (RSA) in futsal players. Thirty-four players (age: 23.7±4.1 years; height: 1.77±0.06 m; body mass: 74.1±8.2 kg) were randomly assigned into three groups: full squat group (SG, n=12), combined full squat and CD group (S+CDG, n=12), and control group (CG, n=10). The RT for SG consisted of full squat with low-load (~45-60% 1RM) and low-volume (2-3 sets and 4-6 repetitions), whereas the S+CDG performed the same RT program combined with loaded CD (2-5 sets of 10 s). Estimated one-repetition maximum (1RMest) and variables derived from RSA test including mean sprint time (RSAmean), best sprint time (RSAbest), percent sprint decrement (Sdec), mean ground contact time (GCTmean) and mean step length (SL) were selected as testing variables. Changes in sprint time and GCT in each sprint were also analysed. Both experimental groups showed significant (P<0.05-0.001) improvements for 1RMest, RSAbest and first and second sprint time. In addition, S+CDG achieved significant (P<0.05-0.001) improvements in RSAmean, sprint time (from fifth to ninth sprint) and GCT (from third to eighth sprint). These results indicate that only 6 weeks of low-load and low-volume RT combined with CD in addition to routine futsal training is enough to improve RSA and strength performance simultaneously in futsal players.

Effects of light-load maximal lifting velocity weight training vs. combined weight training and plyometrics on sprint, vertical jump and strength performance in adult soccer players.

OBJECTIVES: The purpose of this study was to compare the effects of combined light-load maximal lifting velocity weight training (WT) and plyometric training (PT) with WT alone on strength, jump and sprint performance in semiprofessional soccer players. DESIGN: Experimental, pre-post tests measures. METHODS: Thirty adult soccer players were randomly assigned into three groups: WT alone (FSG, n=10), WT combined to jump and sprint exercises (COM, n=10) and control group (CG, n=10). WT consisted of full squat with low load (∼45-60% 1RM) and low volume (4-6 repetitions). Training program was performed twice a week for 6 weeks of competitive season in addition to 4 soccer sessions a week. Sprint time in 10 and 20m, jump height (CMJ), estimated one-repetition maximum (1RMest) and velocity developed against different absolute loads in full squat were measured before and after training period. RESULTS: Both experimental groups showed significant improvements in 1RMest (17.4-13.4%; p<0.001), CMJ (7.1-5.2%; p<0.001), sprint time (3.6-0.7%; p<0.05-0.001) and force-velocity relationships (16.9-6.1%; p<0.05-0.001), whereas no significant gains were found in CG. No significant differences were found between FSG and COM. CONCLUSIONS: Despite FSG resulted of greater increases in strength variables than COM, this may not translate into superior improvements in the sport-related performance. In fact, COM showed higher efficacy of transfer of strength gains to sprint ability. Therefore, these findings suggest that a combined WT and PT program could represent a more efficient method for improving activities which involve acceleration, deceleration and jumps compared to WT alone.

Light-load maximal lifting velocity full squat training program improves important physical and skill characteristics in futsal players.

This study aimed to compare the effect of 6 weeks of resistance training or combined resistance training and change of direction exercises on physical performance and motor skills in futsal players. Thirty-four futsal players were divided into full squat group (SG, n = 12), combined full squat and change of direction exercises group (S+CDG, n = 12) and control group (CG, n = 10). The resistance training for SG consisted of full squat with low load (~45-58% 1RM) and low volume (4-6 repetitions), whereas the S+CDG performed the same resistance training program combined with loaded change of direction. Sprint time in 10 and 20 m, change of direction test, countermovement vertical jump (CMJ) height, maximal strength and force-velocity relationship in full squat exercise, kicking speed ball (BSmean) and repeated sprint ability (RSAmean) were selected as testing variables. Both experimental groups showed significant improvements for CMJ, BSmean and all strength parameters. Only SG resulted in significant sprint gains, whereas S+CDG also achieved significant improvements in RSAmean. The CG remained unchanged after training period. No significant differences were found between both experimental groups. These findings suggest that only 12 sessions of either lightweight resistance training alone, lifting the load at maximal intended velocity or combined with change of direction exercises is enough to improve several physical and skills capacities critical to futsal performance in adult players.

Modulation of the input-output function by GABAA receptor-mediated currents in rat oculomotor nucleus motoneurons.

The neuronal input-output function depends on recruitment threshold and gain of the firing frequency-current (f-I) relationship. These two parameters are positively correlated in ocular motoneurons (MNs) recorded in alert preparation and inhibitory inputs could contribute to this correlation. Phasic inhibition mediated by γ-amino butyric acid (GABA) occurs when a high concentration of GABA at the synaptic cleft activates postsynaptic GABAA receptors, allowing neuronal information transfer. In some neuronal populations, low concentrations of GABA activate non-synaptic GABAA receptors and generate a tonic inhibition, which modulates cell excitability. This study determined how ambient GABA concentrations modulate the input-output relationship of rat oculomotor nucleus MNs. Superfusion of brain slices with GABA (100 µm) produced a GABAA receptor-mediated current that reduced the input resistance, increased the recruitment threshold and shifted the f-I relationship rightward without any change in gain. These modifications did not depend on MN size. In absence of exogenous GABA, gabazine (20 µm; antagonist of GABAA receptors) abolished spontaneous inhibitory postsynaptic currents and revealed a tonic current in MNs. Gabazine increased input resistance and decreased recruitment threshold mainly in larger MNs. The f-I relationship shifted to the left, without any change in gain. Gabazine effects were chiefly due to MN tonic inhibition because tonic current amplitude was five-fold greater than phasic. This study demonstrates a tonic inhibition in ocular MNs that modulates cell excitability depending on cell size. We suggest that GABAA tonic inhibition acting concurrently with glutamate receptors activation could reproduce the positive covariation between threshold and gain reported in alert preparation.

Glutamate modulates the firing rate in oculomotor nucleus motoneurons as a function of the recruitment threshold current.

Studies in alert preparations have demonstrated that ocular motoneurons exhibit a phasic­tonic firing rate related to eye velocity and position, respectively. The slopes of these relationships are higher in motoneurons with higher recruitment threshold and have been proposed to depend upon synaptic input. To investigate this hypothesis, motoneurons of the rat oculomotor nucleus were recorded in a brain slice preparation in control conditions and during glutamate (5 µm) application to the bath. Glutamate did not affect membrane potential or input resistance, but produced a decrease in rheobase and depolarization voltage as a function of the current needed for generating a maintained repetitive discharge (recruitment threshold current). In addition, glutamate compressed the range of recruitment threshold current (0.1­0.4 nA) as compared to the control (0.15­0.7 nA). Glutamate exposed motoneurons showed an increase in the tonic frequency gain and the peak frequency. Such increments depended on the recruitment threshold current and the last recruited motoneurons almost doubled the tonic frequency gain (35.2 vs. 57.9 spikes s(−1) nA(−1)) and the peak frequency (52.4 vs. 102.6 spikes s(−1)). Finally, glutamate increased the spike frequency adaptation due to a significant increase in the phasic firing component as compared to the tonic one. In conclusion, glutamate modulates tonic and phasic discharge properties as a function of the recruitment threshold current and, presumably, motoneuron size. These findings contribute to understand the link between cellular functions and motoneuron discharge during oculomotor behaviour.

GABAergic Projections to the Oculomotor Nucleus in the Goldfish (carassius Auratus).

The mammalian oculomotor nucleus receives a strong γ-aminobutyric acid (GABA)ergic synaptic input, whereas such projections have rarely been reported in fish. In order to determine whether this synaptic organization is preserved across vertebrates, we investigated the GABAergic projections to the oculomotor nucleus in the goldfish by combining retrograde transport of biotin dextran amine, injected into the antidromically identified oculomotor nucleus, and GABA immunohistochemistry. The main source of GABAergic afferents to the oculomotor nucleus was the ipsilateral anterior octaval nucleus, with only a few, if any, GABAergic neurons being located in the contralateral tangential and descending nuclei of the octaval column. In mammals there is a nearly GABAergic inhibitory inputs; thus, the vestibulooculomotor GABAergic circuitry follows a plan that appears to be shared throughout the vertebrate phylogeny. The second major source of GABAergic projections was the rhombencephalic reticular formation, primarily from the medial area but, to a lesser extent, from the inferior area. A few GABAergic oculomotor projecting neurons were also observed in the ipsilateral nucleus of the medial longitudinal fasciculus. The GABAergic projections from neurons located in both the reticular formation surrounding the abducens nucleus and the nucleus of the medial reticular formation have primarily been related to the control of saccadic eye movements. Finally, all retrogradely labeled internuclear neurons of the abducens nucleus, and neurons in the cerebellum (close to the caudal lobe), were negative for GABA. These data suggest that the vestibuloocular and saccadic inhibitory GABAergic systems appear early in vertebrate phylogeny to modulate the firing properties of the oculomotor nucleus motoneurons.