Author(s): GOMES, M., GONÇALVES, A., VILA-CHÃ, C., PEZARAT-CORREIA, P., MENDONCA, G.V., Institution: FACULTY OF HUMAN KINETICS - UNIVERSITY OF LISBON, Country: PORTUGAL, Abstract-ID: 1451

INTRODUCTION:
Concurrent exercise (CE) combines resistance and aerobic exercise to enhance strength (S) and endurance (E). While short-term endurance training increases the H-reflex excitability, resistance training enhances V-wave amplitude, reflecting spinal and supraspinal adaptations, respectively (1). The acute impact of combining both stimuli on the aforementioned parameters remains largely unknown. This study explored H-reflex and V-wave acute changes following single and CE sessions completed in both orders (SE and ES)
METHODS:
Ten healthy, trained males (22.8±2.5yrs) participated in this crossover-design study, with baseline assessments and four randomized exercise sessions (S,E,ES,SE). E sessions involved 30 min of treadmill running at a velocity 25%>1st ventilatory threshold, and S sessions included back squats with varied loads (40-90%1RM) and loaded/unloaded jumps. All CE sessions included a 20-min rest between modalities. Assessments of soleus evoked V-wave amplitude, H-reflex recruitment curves, maximal voluntary contraction (MVC) and rate of torque development (RTD) of the dominant limb plantar flexors were conducted at baseline and immediately after each session. Paired samples t-tests between baseline and post-session evaluated the individual impact of each session, and a one-way repeated measures ANOVA assessed differences between session types. Significance was set at p<0.05
RESULTS:
MVC and peak RTD of the plantar flexors significantly decreased in all sessions (-13.9 to -19.1% and -24.1 to -31.3%, respectively, p<0.05). RTD during the first milliseconds of contraction was unaffected, but subsequent epochs (50-150ms) showed a larger decline in all sessions, with significant differences between E (-40.2±17.5%) and S (-19.4±14.1%) (p<0.05). This was concomitant with similar declines in soleus electromyography amplitude across all sessions (-36 to -62%, p<0.05). No changes were observed in M-wave amplitude. The normalized V-wave amplitude decreased similarly after all sessions (-13 to -30%, p<0.05). Sessions incorporating E exercise reduced the maximum normalized H-reflex amplitude (-17.9 to -25.6%) with significant differences from S session (p<0.05). H-reflex excitability threshold remained unchanged, while the slope of the ascending limb of the recruitment curve significantly decreased after both CE sessions (-48.3 to -49.8%, p<0.05)
CONCLUSION:
E exercise alone reduces the MVC and RTD of the plantar flexors, along with the neural drive to the active muscles. Such effects might compromise the quality of subsequent S sessions. Regardless of training sequence, CE acutely reduces the excitability of the H reflex, which suggests an acute impact on modulation at the spinal level. Ultimately, this indicates that altered H-reflex excitability may have an etiological role in the CE interference effect and this is novel.

1.Vila-Chã C,Falla D,Correia M, Farina D. Changes in H-reflex and V-wave following short-term endurance and strength training. J Appl Physiol (2012).112(1):54-63