Abstract
Intermittent hypoxic resistance training (IHRT) may help to maximize the adaptations following resistance training, although conflicting evidence is available. The aim of this study was to explore the influence of moderate altitude on the functional, neural and muscle architecture responses of the quadriceps muscles following a power-oriented IHRT intervention. Twenty-four active males completed two 4-week consecutive training blocks comprising general strengthening exercises (weeks 1–4) and power-oriented resistance training (weeks 5–8). Training sessions were conducted twice a week at moderate altitude (2320 m; IHRT, n = 13) or normoxia (690 m; NT, n = 11). Training intensity during the second training block was set to the individual load corresponding to a barbell mean propulsive velocity of 1 m·s−1. Pre-post assessments, performed under normoxic conditions, comprised quadriceps muscle architecture (thickness, pennation angle and fascicle length), isometric maximal (MVF) and explosive strength, and voluntary muscle activation. Dynamic strength performance was assessed through the force-velocity relationship (F0, V0, P0) and a repeated CMJ test (CMJ15MP). Region-specific muscle thickness changes were observed in both training groups (p < 0.001, = 0.02). A small opposite trend in pennation angle changes was observed (ES [90% CI]: −0.33 [−0.65, −0.01] vs. 0.11 [−0.44, 0.6], in the IHRT and NT group, respectively; p = 0.094, = 0.02). Both training groups showed similar improvements in MVF (ES: 0.38 [0.20, 0.56] vs. 0.55 [0.29, 0.80], in the IHRT and NT group, respectively; p = 0.645, < 0.01), F0 (ES: 0.41 [−0.03, 0.85] vs. 0.52 [0.04, 0.99], in the IHRT and NT group, respectively; p = 0.569, < 0.01) and P0 (ES: 0.53 [0.07, 0.98] vs. 0.19 [−0.06, 0.44], in the IHRT and NT group, respectively; p = 0.320, < 0.01). No meaningful changes in explosive strength performance were observed. In conclusion, contrary to earlier adverse associations between altitude and resistance-training muscle adaptations, similar anatomical and functional muscle strength responses can be achieved in both environmental conditions. The observed region-specific muscle thickness changes may encourage further research on the potential influence of IHRT on muscle morphological changes.
Highlights
Since the well-established “live high, train low” altitude training studies developed in the nineties (Levine and Stray-Gundersen, 1997), the use of hypoxia in sport has evolved from a mainly hematological aim to a broader scope embracing neuromuscular aspects (Scott et al, 2014b; Brocherie et al, 2015)
The present study examined the effects of an 8-week resistance training intervention, under normoxic or moderate altitude environmental conditions, on the functional, voluntary EMG activation and morphological adaptations of the quadriceps muscles
Compared to NT, the Intermittent hypoxic resistance training (IHRT) intervention exhibited similar maximal strength responses assessed either from the FVrelationship (i.e., F0) or using a single-leg knee extension isometric maximal voluntary contractions (MVC). These results contribute to the conflicting IHRT research available showing significant (Inness et al, 2016; Yan et al, 2016) and non-meaningful changes in maximal strength compared to training under normoxic conditions (Ho et al, 2014; Kurobe et al, 2015)
Summary
Since the well-established “live high, train low” altitude training studies developed in the nineties (Levine and Stray-Gundersen, 1997), the use of hypoxia in sport has evolved from a mainly hematological aim to a broader scope embracing neuromuscular aspects (Scott et al, 2014b; Brocherie et al, 2015). Despite greater acute hormonal and metabolic stress responses following resistance exercise under hypoxic conditions (Kon et al, 2010; Kurobe et al, 2015), there are studies reporting both significant (Nishimura et al, 2010; Manimmanakorn et al, 2013b; Kurobe et al, 2015) and no meaningful effects (Friedmann et al, 2003; Ho et al, 2014; Kon et al, 2014) of IHRT on the muscle cross-sectional area (CSA). Resistance training practices aiming to enhance athletic performance often comprise maximal intended explosive efforts leading to both training-specific structural (Blazevich et al, 2003) and neural adaptations (Buckthorpe et al, 2015). No previous studies have explored the potential effects of IHRT on other functionally relevant structural (i.e., muscle architecture) and neural (i.e., rate of muscle activation) factors
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