Tissue oxygenation response to systemic and localised hypoxia during intermittent isometric contractions.

Abstract

The use of either blood flow restriction (BFR) and systemic hypoxia (HYP) during resistance exercise has been shown to increase hypertrophy and strength to a greater extent compared to traditional resistance exercise alone. However, the mechanisms underpinning these enhanced adaptations remain to be elucidated. Differences in skeletal muscle oxygenation may be one of several factors that leads to increased hypertrophy and strength with BFR and HYP. Nevertheless, this has been sparsely investigated. High intensity resistance exercise is also accompanied by an increase in oxidative stress, providing beneficial hypertrophic signalling. The addition of BFR has been observed to decrease these beneficial signals and the effect of HYP is unknown. PURPOSE: To investigate the skeletal muscle oxygenation and oxidative stress response during moderate intensity rhythmic isometric handgrip exercise with BFR, HYP, and resistance exercise alone. In addition, to observe the perceived pain (PP) response to these novel exercise modalities during exercise. METHODS: Eight recreationally active males (23 ± 1 yr, 76 ± 10 kg, 175 ± 6 cm) completed three sets of 45 repetitions of isometric handgrip exercise (60% 1RM) either with BFR (80 mmHg proximal cuff) 5 minutes pre and during exercise, with HYP (14% O2) 5 minutes pre and during exercise or with resistance exercise alone (CON). Exercise was completed in a supine position, with one-minute rest in-between sets. Skeletal muscle oxygenation was measured throughout using a dual wave near infrared spectroscopy (NIRS) device placed on the forearm flexors, with output variables of tissue saturation index (TSI), oxygenated haemoglobin (O2Hb), de-oxygenated haemoglobin (HHb) and total haemoglobin (THb). NIRS variables were reported as a delta from a pre-exercise control period and represented a change from baseline. Oxidative stress was measured in whole blood via glutathione ratio (GSSG:GTSH). PP was measured during each exercise set with a visual analogue scale. RESULTS: TSI was lower in BFR (-11.5 ± 10.3 %) compared to CON (-1.3 ± 5.1%, p = 0.007) and lower with no significant difference compared to HYP (-4.5 ± 5.1 %, p = 0.059), there was no difference between CON and HYP (p > 0.05). There was no difference in O2Hb between conditions (p >0.84). HHb was higher in BFR (13.9 ± 5.1 μmol) compared to both CON (2.06 ± 5.87 μmol, p = 0.001) and HYP (6.83 ± 6.11 μmol, p = 0.042), with no difference between CON and HYP (p > 0.05). THb was significantly higher in BFR (9.41 ± 9.54 μmol) compared to both CON (-1.22 ± 5.50 μmol, p = 0.001) and HYP (1.59 ± 5.04 μmol, p = 0.008), with no difference between CON and HYP (p > 0.05). There was no increase in GSSG:GTSH pre-post exercise with no significant difference between conditions (p > 0.085). PP was higher in the BFR condition (6 ± 1 a.u) compared to CON (2 ± 2 a.u, p = 0.001) and HYP (2 ± 2 a.u, p = 0.001), with no difference between CON and HYP (p > 0.05). CONCLUSION: Moderate intensity rhythmic isometric handgrip exercise with BFR results in an increased blood volume (THb), decreased clearance of HHb and lower TSI compared to HYP and CON, however O2Hb delivery remains similar between conditions. The differences in skeletal muscle oxygenation with the addition of BFR to resistance exercise provide further insight into the mechanisms acute of BFR; however, further investigation is required with over a prolonged period of training. The current protocol did not elicit a whole blood oxidative stress response in the form of increased GSSG:TGSH, therefore the role of oxidative stress could not be determined.