Author(s): GAMERO DEL CASTILLO, D., PONTES, M., BAUDRY, S., Institution: UNIVERSITÉ LIBRE DE BRUXELLES - FSM, Country: BELGIUM, Abstract-ID: 2052

INTRODUCTION:
David Gamero-delCastillo1, Matheus Pontes2 and Stephane Baudry1

1Laboratory of Applied Biology and Research Unit in Applied Neurophysiology (LABNeuro), Université Libre de Bruxelles, Brussels, Belgium
2Department of Physiotherapy, LUNEX International University of Health, Exercise and Sports, Differdange, Luxembourg

Resistance exercise differs significantly in nature and manipulating training variables [including intensity expressed as % of the one repetition maximal (1RM)] allows for specific adaptive changes which may include gains in muscle mass and maximal strength. Two types of loading in strength training protocols are mainly used, hypertrophic and maximal loading, which can induce different acute responses (1). This study aimed to measure acute neuromuscular changes induced by two mechanical loading patterns commonly used in field settings.
METHODS:
Sixteen men strength training practitioners, [mean(SD); age 26(2) yr., body mass 79(8) kg, height 181(5) cm] performed two sessions in random order on a leg press machine. One session consisted of 4 sets of 4 repetitions at 85% 1RM (150s rest between sets) while the other consisted of 4 sets of 10 repetitions at 70% 1RM, (90s rest between sets). Measurement techniques, used immediately before and after the session, included proximal femoral nerve tetanic stimulations (50 pulses, 50Hz), maximal voluntary isometric contraction (MVIC), electromyography (EMG) of vastus lateralis (VL) and rectus femoris (RF), and tissue oxygenation index (TOI). In addition, transcranial magnetic stimulation (TMS) of the motor cortex was used to elicit motor-evoked potential (MEP) in VL during repetitions performed during the training sessions.
RESULTS:
Following both protocols MVIC force decreased by -31(31)% and -8(7)%, as tetanic torque (p<0.001) by -30(20)% and -13(20)%, after 4x10 and 4x4 respectively. VL EMG activity decreased (p<0.05) by -24(31)% and -19(25)% after both 4x10 and 4x4 but decreased only after 4x10; (-22(17)%) for RF. For VL TOI, was reduced (p<0.05) for both schemes, particularly during the 4x10, (-26(4)%; 4x4, -16(2)%.
During the sessions, MEP amplitude increased (p<0.05), by +65(25)%; and +40(20)% during 4x4 and 4x10, respectively. Results suggest a greater metabolic stress especially after 4x10, as assessed by TOI. Metabolic stress may impact force production (2) as observed by decreased MVIC, tetanic torque, and EMG activity. Changes in MEP may indicate a potential modulation in neuromuscular excitability (3,4).

CONCLUSION:
Voluntary and tetanic force decreased in the same proportions within protocols, suggesting that the changes are mainly localized at the peripheral level. In addition, the more marked reduction in strength for the 4x10 is probably associated with metabolic changes as suggested by TOI. These findings highlight the specific neuromuscular responses through two mechanical loading patterns, used in field settings.