Oxygen Uptake Slow Component and the Efficiency of Resistance Exercises

ABSTRACT

Garnacho-Castaño, MV, Albesa-Albiol, L, Serra-Payá, N, Gomis Bataller, M, Pleguezuelos Cobo, E, Guirao Cano, L, Guodemar-Pérez, J, Carbonell, T, Domínguez, R, and Maté-Muñoz, JL. Oxygen uptake slow component and the efficiency of resistance exercises. J Strength Cond Res 35(4): 1014-1022, 2021-This study aimed to evaluate oxygen uptake slow component (V̇o2sc) and mechanical economy/efficiency in half squat (HS) exercise during constant-load tests conducted at lactate threshold (LT) intensity. Nineteen healthy young men completed 3 HS exercise tests separated by 48-hour rest periods: 1 repetition maximum (1RM), incremental-load HS test to establish the %1RM corresponding to the LT, and constant-load HS test at the LT. During the last test, cardiorespiratory, lactate, and mechanical responses were monitored. Fatigue in the lower limbs was assessed before and after the constant-load test using a countermovement jump test. A slight and sustained increase of the V̇o2sc and energy expended (EE) was observed (p < 0.001). In blood lactate, no differences were observed between set 3 to set 21 (p > 0.05). A slight and sustained decrease of half squat efficiency and gross mechanical efficiency (GME) was detected (p < 0.001). Significant inverse correlations were observed between V̇o2 and GME (r = -0.93, p < 0.001). Inverse correlations were detected between EE and GME (r = -0.94, p < 0.001). Significant losses were observed in jump height ability and in mean power output (p < 0.001) in response to the constant-load HS test. In conclusion, V̇o2sc and EE tended to rise slowly during constant-load HS exercise testing. This slight increase was associated with lowered efficiency throughout constant-load test and a decrease in jump capacity after testing. These findings would allow to elucidate the underlying fatigue mechanisms produced by resistance exercises in a constant-load test at LT intensity.

The Relationship between Resistance Exercise Performance and Ventilatory Efficiency after Beetroot Juice Intake in Well-Trained Athletes

The assessment of ventilatory efficiency is critical to understanding the matching of ventilation (VE) and perfusion in the lungs during exercise. This study aimed to establish a causal physiological relationship between ventilatory efficiency and resistance exercise performance after beetroot juice (BJ) intake. Eleven well-trained males performed a resistance exercise test after drinking 140 mL of BJ (~12.8 mmol NO₃^-) or a placebo (PL). Ventilatory efficiency was assessed by the VE•VCO₂^-1 slope, the oxygen uptake efficiency slope and the partial pressure of end-tidal carbon dioxide (PetCO₂). The two experimental conditions were controlled using a randomized, double-blind crossover design. The resistance exercise test involved repeating the same routine twice, which consisted of wall ball shots plus a full squat (FS) with a 3 min rest or without a rest between the two exercises. A higher weight lifted was detected in the FS exercise after BJ intake compared with the PL during the first routine (p = 0.004). BJ improved the VE•VCO₂^-1 slope and the PetCO₂ during the FS exercise in the first routine and at rest (p < 0.05). BJ intake improved the VE•VCO₂^-1 slope and the PetCO₂ coinciding with the resistance exercise performance. The ergogenic effect of BJ could be induced under aerobic conditions at rest.

Understanding the effects of beetroot juice intake on CrossFit performance by assessing hormonal, metabolic and mechanical response: a randomized, double-blind, crossover design

BACKGROUND

Acute beetroot juice (BJ) intake has shown to enhance aerobic and anaerobic performance. However, no studies have evaluated the effects of BJ intake on CrossFit (CF) performance by linking hormonal, metabolic, and mechanical responses. The purpose of this study was to determine the causal physiological association between hormonal, metabolic and mechanical responses, and CF workouts performance after acute BJ intake.

METHODS

Twelve well-trained male practitioners undertook a CF workout after drinking 140 mL of BJ (~ 12.8 mmol NO3-) or placebo. The two experimental conditions (BJ or placebo) were administered using a randomized, double-blind, crossover design. The CF workout consisted of repeating the same exercise routine twice: Wall ball (WB) shots plus full back squat (FBS) with 3-min rest (1st routine) or without rest (2nd routine) between the two exercises. A 3-min rest was established between the two exercise routines.

RESULTS

An interaction effect was observed in the number of repetitions performed (p = 0.04). The Bonferroni test determined a higher number of repetitions after BJ than placebo intake when a 3-min rest between WB and FBS (1st routine) was established (p = 0.007). An interaction effect was detected in cortisol response (p = 0.04). Cortisol showed a higher increase after BJ compared to placebo intake (76% vs. 36%, respectively). No interaction effect was observed in the testosterone and testosterone/cortisol ratio (p > 0.05). A significant interaction effect was found in oxygen saturation (p = 0.01). A greater oxygen saturation drop was observed in BJ compared to placebo (p <  0.05). An interaction effect was verified in muscular fatigue (p = 0.03) with a higher muscular fatigue being observed with BJ than placebo (p = 0.02).

CONCLUSIONS

BJ intake improved anaerobic performance only after the recovery time between exercises. This increase in performance in the first routine probably generated greater hypoxia in the muscle mass involved, possibly conditioning post-exercise performance. This was observed with a fall in oxygen saturation and in muscle fatigue measured at the end of the CF workout. The greatest perceived changes in cortisol levels after BJ intake could be attributed to the nitrate-nitrite-nitric oxide pathway.

The Slow Component of Oxygen Uptake and Efficiency in Resistance Exercises: A Comparison With Endurance Exercises

Introduction

There is a lack of information regarding the slow component of oxygen uptake (VO₂sc) and efficiency/economy in resistance exercises despite the crucial role played in endurance performance.

Purpose

this study aimed to compare the VO₂sc, efficiency/economy, metabolic, cardiorespiratory responses, rating of perceived effort and mechanical fatigue between cycling and half-squat (HS) exercises during a constant-load test at lactate threshold (LT₁) intensity.

Methods

Twenty-one healthy men were randomly assigned in a crossover design to perform cycle-ergometer or HS tests. The order of the two cycle ergometer tests was an incremental test for determining load-intensity in watts (W) at LT₁, followed by a constant-load test at the LT₁ intensity. For the three HS tests, the order was a 1RM test to determine the load (kg) corresponding to the 1RM percentages to be used during the second test, incremental HS exercise to establish the load (kg) at the LT₁ intensity, and finally, a constant-load HS test at the LT₁ intensity. A rest period of 48 h between each test was established. During the HS and cycle-ergometer constant-load tests, cardiorespiratory and metabolic responses were recorded. Lower limbs fatigue was determined by a jump test before and after the constant-load tests.

Results

A significant exercise mode × time interaction effect was detected in VO₂, heart rate, energy expenditure (EE), gross efficiency (GE), and economy (p < 0.05). A significant and sustained VO₂ raise was confirmed in HS exercise (p < 0.05) and a steady-state VO₂ was revealed in cycle-ergometer. A higher GE and economy were obtained in HS test than in cycle-ergometer exercise (p < 0.001). In both exercises, a non-significant decrease was observed in GE and economy (p > 0.05). Lower limbs fatigue was only detected after constant-load HS test.

Conclusion

Although the VO₂, heart rate and EE responses were higher in cycling exercise, the constant-load HS test induced a greater VO₂sc and EE raise than the cycling test in a predominantly aerobic metabolism. These results could explain a decrease observed in jump performance only after HS test. GE and economy could benefit from the eccentric phase of the HS exercise.