High intensity interval training versus moderate intensity continuous training to maximize neuromuscular adaptations
Abstract
High intensity interval training (HIIT) is defined as a group of vigorous intensity bouts separated by periods of rest. Although many studies have been conducted on the effects of HIIT, few investigations have focused on neuromuscular adaptations in response to HIIT versus moderate intensity continuous training (MICT). The purpose of this study was to investigate the neuromuscular adaptations following low-volume HIIT designs (i.e., ultrashort-HIIT, Tabata-HIIT) compared to high-volume MICT on an air-resistance fan bike. Forty-seven recreationally active individuals volunteered to participate, and were randomly assigned to ultrashort-HIIT, Tabata-HIIT, and MICT. The intervention was performed 3 days per week for 4 weeks. MICT sessions included 30 min of cycling at 75% of maximal heart rate reserve, while HIIT protocols consisted of 3 sets of 8 intervals at maximal effort intensity. Ultrashort-HIIT and Tabata-HIIT protocols were performed with 10s:5s and 20s:10s work-to-rest ratios and provided with 2.5- and 5-min recovery periods between sets, respectively. Testing procedures were completed pre and post intervention, consisting of rate of torque development (RTD); peak torque (PT) during maximal voluntary isometric contraction (MIVC) and submaximal contractions leg extension; rectus femoris (RF) and vastus lateralis (VL) early phase and maximal activations during PT (i.e., PT-RMS) and entire contraction (i.e., pRMS); RF and VL muscle cross-sectional area (mCSA) and echo intensity (EI). Two-way mixed factorial ANOVAs were calculated for statistical analyses. There was a significant Time x Group interaction effect in RF PT-RMS during 70% MVIC (p = 0.015) and VL EI (p = 0.023). Tabata-HIIT elicited greater improvements in RF PT-RMS during 70% MVIC, while ultrashort-HIIT showed greater decreases in VL EI than other groups. Significant main effect of Time was observed in RTD50 (p = 0.010), RTD75 (p = 0.044), RTD100 (p = 0.040), RTD100-200 (p = 0.027), pRMS MVIC (p = 0.001), PT-RMS (p = 0.003), pRMS (p = 0.012), PT-RMS (p = 0.017), pRMS 70% MVIC (p = 0.009), pRMS 100% MVIC (p = 0.001), r-pRMS 100% (p = 0.047), RF mCSA (p < 0.001), VL mCSA (p < 0.001), and RF EI (p = 0.035). No significant interactions nor main effects (p > 0.05) were observed in PT, RF and VL early phase activations, and VL maximal activation. These findings concluded that low-volume HIIT designs are "time-efficient" exercise mode to induce neuromuscular and muscular morphological adaptations compared to high-volume MICT. Furthermore, HIIT has the potential to elicit greater neuromuscular adaptations in comparison to traditionally prescribed MICT.
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- OSU Dissertations [11222]