Muscle Fatigue Is Attenuated When Applying Intermittent Compared With Continuous Blood Flow Restriction During Endurance Cycling.

PURPOSE: The aim of this study was to identify a blood-flow-restriction (BFR) endurance exercise protocol that maximizes metabolic strain and minimizes muscle fatigue. METHODS: Twelve healthy participants accomplished 5 different interval cycling endurance exercises (2-min work, 1-min rest) in a randomized order: (1) control, low intensity with unrestricted blood flow (CON30); (2) low intensity with intermittent BFR (i-BFR30, ∼150 mm Hg); (3) low intensity with continuous BFR (c-BFR, ∼100 mm Hg); (4) unloaded cycling with i-BFR0 (∼150 mm Hg); and (5) high intensity (HI) with unrestricted blood flow. Force production, creatine kinase activity, antioxidant markers, blood pH, and potassium (K+) were measured in a range of 5 minutes before and after each cycling exercise protocol. RESULTS: HI showed the highest reduction (Δ = -0.26 [0.05], d = 5.6) on blood pH. Delta pH for c-BRF30 (Δ = -0.02 [0.03], d = 0.8) and Δ pH for i-BRF30 (Δ = -0.04 [0.03], d = 1.6) were different from each other, and both were higher compared with CON30 (Δ = 0.03 [0.03]). There was significant before-to-after force loss following HI (Δ = 55 [40] N·m-1, d = 1.5) and c-BFR30 (Δ = 27 [21] N·m-1, d = 0.7) protocols only, which were accompanied by significant increases in K+ (HI: Δ = 0.94 [0.65] mmol·L-1, d = 1.8; c-BFR30: Δ = 0.72 [0.85] mmol·L-1, d = 1.2). Moreover, all BFR conditions elicited slight increases in plasma creatine kinase, but not for HI and CON30. Glutathione changes from before to after were significant for all BFR conditions and HI, but not for CON30. CONCLUSIONS: The attenuation in fatigue-induced reductions in maximal force suggests that i-BFR exercise could be preferable to c-BFR in improving exercise capacity, with considerably less biologic stress elicited from HI exercises.

Mechanical power during an incremental test can be estimated from 2000-m rowing ergometer performance.

BACKGROUND: This study aimed to identify the relationship between the mean power output of 2000-m rowing ergometer performance with the peak power output obtained during an incremental test, in addition to verifying the possibility of using the 2000-m mean power as an intensity associated with V̇O2max. METHODS: Nineteen rowers (age 25.5±10.6 years; V̇O2peak: 65.4±5.8 mL/kg/min) completed an incremental test followed by a 2000-m familiarization test (day 1) and a 2000-m rowing ergometer test (day 2). During the incremental test, the peak power output (PV̇O2peak) and the exercise intensity thresholds were determined. The maximal oxygen uptake (V̇O2peak) was analyzed in both tests. RESULTS: The PV̇O2peak (284.8±44.7 W) presented the highest correlation coefficient (r=0.978) with 2000-m mean power (284.2±49.9 W) and was the only one included in stepwise regression explaining 96% of 2000-m mean power. V̇O2peak was lower in the incremental test (4.69±0.61 L/min) compared with the 2000-m rowing ergometer test (4.86±0.63 L/min; P=0.01) with a small bias limits of agreement (0.16±0.53 L/min). CONCLUSIONS: 2000-m mean power is a valid tool to estimate the PV̇O2peak and allow the achievement of V̇O2peak. Furthermore, the PV̇O2peak was the most important predictor of performance.

Association Between Deoxygenated Hemoglobin Breaking Point, Anaerobic Threshold, and Rowing Performance.

PURPOSE: To compare the intensity and physiological responses of deoxygenated hemoglobin breaking point ([HHb]BP) and anaerobic threshold (AnT) during an incremental test and to verify their association with 2000-m rowing-ergometer performance in well-trained rowers. METHODS: A total of 13 male rowers (mean [SD] age = 24 [11] y and V˙O2peak = 63.7 [6.1] mL·kg-1·min-1) performed a step incremental test. Gas exchange, vastus lateralis [HHb], and blood lactate concentration were measured. Power output, V˙O2, and heart rate of [HHb]BP and AnT were determined and compared with each other. A 2000-m test was performed in another visit. RESULTS: No differences were found between [HHb]BP and AnT in the power output (236 [31] vs 234 [31] W; Δ = 0.7%), 95% confidence interval [CI] 6.7%), V˙O2 (4.2 [0.5] vs 4.3 [0.4] L·min-1; Δ = -0.8%, 95% CI 4.0%), or heart rate (180 [16] vs 182 [12] beats·min-1; Δ = -1.6%, 95% CI 2.1%); however, there was high typical error of estimate (TEE) and wide 95% limits of agreement (LoA) for power output (TEE 10.7%, LoA 54.1-50.6 W), V˙O2 (TEE 5.9%, LoA -0.57 to 0.63 L·min-1), and heart rate (TEE 2.4%, LoA -9.6 to 14.7 beats·min-1). Significant correlations were observed between [HHb]BP (r = .70) and AnT (r = .89) with 2000-m mean power. CONCLUSIONS: These results demonstrate a breaking point in [HHb] of the vastus lateralis muscle during the incremental test that is capable of distinguishing rowers with different performance levels. However, the high random error would compromise the use of [HHb]BP for training and testing in rowing.

Intracellular shuttle: the lactate aerobic metabolism.

Lactate is a highly dynamic metabolite that can be used as a fuel by several cells of the human body, particularly during physical exercise. Traditionally, it has been believed that the first step of lactate oxidation occurs in cytosol; however, this idea was recently challenged. A new hypothesis has been presented based on the fact that lactate-to-pyruvate conversion cannot occur in cytosol, because the LDH enzyme characteristics and cytosolic environment do not allow the reaction in this way. Instead, the Intracellular Lactate Shuttle hypothesis states that lactate first enters in mitochondria and only then is metabolized. In several tissues of the human body this idea is well accepted but is quite resistant in skeletal muscle. In this paper, we will present not only the studies which are protagonists in this discussion, but the potential mechanism by which this oxidation occurs and also a link between lactate and mitochondrial proliferation. This new perspective brings some implications and comes to change our understanding of the interaction between the energy systems, because the product of one serves as a substrate for the other.