The Effect of Lower-Body Positive Pressure on the Cardiorespiratory Response at Rest and during Submaximal Running Exercise

The effect of ischemic preconditioning on repeated sprint cycling performance: a randomized crossover study

BACKGROUND

Ischemic preconditioning (IPC) has been suggested to improve exercise performance by 1-8%. Prior research concerning its impact on short-duration exercises, such as sprints, has been limited and yielded conflicting results. The aim of this study, which included a non-occlusion-based placebo control, was to determine whether IPC improves repeated sprint performance in a manner that accounted for psychophysiological effects.

METHODS

Twenty-two healthy males participated in this study, which employed a randomized crossover design. Following the 10-min baseline period, participants received intervention under four different conditions: 1) no-intervention control (CON); 2) non-occlusion-based placebo control (SHAM); 3) remote IPC (RIPC); and 4) local IPC (LIPC). Participants then performed a standardized repeated sprint cycling (5×10s maximal cycling sprint, separated by a 40-s rest in each set).

RESULTS

Repeated sprint performance, as indexed by average power output, peak power output, and total work, the improvement was observed in the RIPC and LIPC during the initial phase (set 1-3) when compared with CON (P<0.05). SHAM condition also showed an increase in peak power output in the set 1 (CON 9.97±1.05 vs. SHAM 10.30±1.13 w/kg, P<0.05), which may represent a psychophysiological component in the IPC-induced improvement. Higher lactate concertation was found in the SHAM and LIPC groups, than in the CON group, 5 minutes after the exercise (CON 15.72±0.68 vs. SHAM 16.82±0.41 vs. LIPC 17.19±0.39 mmol/L, P<0.0001 for both, respectively).

CONCLUSIONS

In conclusion, LIPC enhanced repeated sprint cycling performance during the initial phase, beyond what could be accounted for entirely by a psychophysiological effect. The improvement associated with RIPC, however, did not surpass the effect of a placebo intervention.

Molecular regulation of skeletal muscle mitochondrial biogenesis following blood flow-restricted aerobic exercise: a call to action

Blood flow-restricted (BFR) exercise can induce training adaptations comparable to those observed following training in free flow conditions. However, little is known about the acute responses within skeletal muscle following BFR aerobic exercise (AE). Moreover, although preliminary evidence suggests chronic BFR AE may augment certain training adaptations in skeletal muscle mitochondria more than non-BFR AE, the underlying mechanisms are poorly understood. In this review, we summarise the acute BFR AE literature examining mitochondrial biogenic signalling pathways and provide insight into mechanisms linked to skeletal muscle remodelling following BFR AE. Specifically, we focus on signalling pathways potentially contributing to augmented peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) mRNA following work-rate-matched BFR AE compared with non-BFR AE. We present evidence suggesting reductions in muscle oxygenation during acute BFR AE lead to increased intracellular energetic stress, AMP-activated protein kinase (AMPK) activation and PGC-1α mRNA. In addition, we briefly discuss mitochondrial adaptations to BFR aerobic training, and we assess the risk of bias using the Cochrane Collaboration risk of bias assessment tool. We ultimately call for several straightforward modifications to help minimise bias in future BFR AE studies.

Effect of Uphill Running on VO2, Heart Rate and Lactate Accumulation on Lower Body Positive Pressure Treadmills

Lower body positive pressure treadmills (LBPPTs) as a strategy to reduce musculoskeletal load are becoming more common as part of sports conditioning, although the requisite physiological parameters are unclear. To elucidate their role, ten well-trained runners (30.2 ± 3.4 years; VO_2max: 60.3 ± 4.2 mL kg^-1 min^-1) ran at 70% of their individual velocity at VO_2max (vVO_2max) on a LBPPT at 80% body weight support (80% BW_Set) and 90% body weight support (90% BW_Set), at 0%, 2% and 7% incline. Oxygen consumption (VO₂), heart rate (HR) and blood lactate accumulation (LA) were monitored. It was found that an increase in incline led to increased VO₂ values of 6.8 ± 0.8 mL kg^-1 min^-1 (0% vs. 7%, p < 0.001) and 5.4 ± 0.8 mL kg^-1 min^-1 (2% vs. 7%, p < 0.001). Between 80% BW_Set and 90% BW_Set, there were VO₂ differences of 3.3 ± 0.2 mL kg^-1 min^-1 (p < 0.001). HR increased with incline by 12 ± 2 bpm (0% vs. 7%, p < 0.05) and 10 ± 2 bpm (2% vs. 7%, p < 0.05). From 80% BW_Set to 90% BW_Set, HR increases of 6 ± 1 bpm (p < 0.001) were observed. Additionally, LA values showed differences of 0.10 ± 0.02 mmol l^-1 between 80% BW_Set and 90% BW_Set. Those results suggest that on a LBPPT, a 2% incline (at 70% vVO_2max) is not yet sufficient to produce significant physiological changes in VO₂, HR and LA-as opposed to running on conventional treadmills, where significant changes are measured. However, a 7% incline increases VO₂ and HR significantly. Bringing together physiological and biomechanical factors from previous studies into this practical context, it appears that a 7% incline (at 80% BW_Set) may be used to keep VO₂ and HR load unchanged as compared to unsupported running, while biomechanical stress is substantially reduced.

Priming the cardiodynamic phase of pulmonary oxygen uptake through voluntary modulations of the respiratory pump at the onset of exercise

NEW FINDINGS

What is the central question of this study? The initial increase in oxygen uptake ( V ̇ O 2 ) at exercise onset results from pulmonary perfusion changes secondary to an increased venous return. Breathing mechanics contribute to venous return through abdominal and intrathoracic pressures variation. Can voluntary breathing techniques (abdominal or rib cage breathing) increase venous return and improve V ̇ O 2 at exercise onset? What is the main finding and its importance? Abdominal and rib cage breathing increase venous return and V ̇ O 2 at exercise onset. This mechanism could be clinically relevant in patients with impaired cardiac function limiting oxygen transport.

ABSTRACT

We examined how different breathing patterns can modulate venous return and alveolar gas transfer during exercise transients in humans. Ten healthy men transitioned from rest to moderate cycling while breathing spontaneously (SP) or with voluntary increases in abdominal (AB) or intrathoracic (RC) pressure swings. We used double body plethysmography to determine blood displacements between the trunk and the extremities (V_bs ). From continuous signals of airflow and O₂ fraction, we calculated breath-by-breath oxygen uptake at the mouth and used optoelectronic plethysmography to correct for lung O₂ store changes and calculate alveolar O₂ transfer ( V ̇ O 2 A ). Oesophageal (P_oes ) and gastric (P_ga ) pressures were monitored using balloon-tipped catheters. Cardiac stroke volume was measured using impedance cardiography. During the cardiodynamic phase (Φ1) of V ̇ O 2 A -on kinetics (20 s following exercise onset), AB and RC increased total alveolar oxygen transfer compared to SP (227 ± 32, P = 0.019 vs. 235 ± 27, P = 0.001 vs. 206 ± 20 ml, mean ± SD). P_ga and P_oes swings increased with AB (by 24.4 ± 9.6 cmH₂ O, P < 0.001) and RC (by 14.5 ± 5.7 cmH₂ O, P < 0.001), respectively. AB yielded a greater increase in intra-breath V_bs swings compared with RC and SP (+0.30 ± 0.14 vs. +0.16 ± 0.11, P < 0.001 vs. +0.10 ± 0.05 ml, P = 0.006) and increased the sum of stroke volumes compared to SP (4.47 ± 1.28 vs. 3.89 ± 0.96 litres, P = 0.053), while RC produced significant central blood translocation from the extremities compared with SP (by 493 ± 311 ml, P < 0.001). Our findings indicate that combining exercise onset with AB or RC increases venous return, thus increasing mass oxygen transport above metabolic consumption during Φ1 and limiting the oxygen deficit incurred.