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Graded exercise test with or without load carriage similarly measures maximal oxygen uptake in young males and females.

ABSTRACT: The aim of this was to compare the effects of the graded exercise test (GXT) with or without load carriage on maximal oxygen uptake ([Formula: see text]) heart rate (HR), and expired ventilation ([Formula: see text]) and blood lactate in young healthy males and females. The study included ten females (age:20.2±0.7 yrs) and ten males (age:19.5±0.7 yrs) who performed the modified Bruce protocol at five load conditions; unloaded, 5, 10, 15, and 20% of body weight (BW) (kg). All the tests were performed in random order, at least 48 hours apart. During the GXTs, HR, [Formula: see text], [Formula: see text], workload and test duration were recorded and blood lactate concentration was measured before and immediately after the GXTs. [Formula: see text] remained unchanged during the GXTs in load and unloaded conditions for both sexes (p>0.05). Test duration was significantly less in females during the GXT with 15% BW (15.9±0.51 min vs. 18.1±1.14 min; p = 0.014) and 20% BW load carriage (15.2±0.75 min vs. 18.1±1.14 min; p = 0.020), compared to the unloaded GXT. Males showed significant decrease in the test duration during the GXT with load 15% BW (20.5±0.53 min vs. 22.8±0.61 min; p = 0.047) and with 20% BW (19.6±0.42 min vs. 22.8±0.71 min; p = 0.004), compared to the GXT with 5% BW. [Formula: see text] statistically decreased in female subjects only at 15% BW compared to 20% BW (15% BW = 77.9 ± 10.5 L/min vs. 15% BW = 72.0 ± 10.9 L/min; p = 0.045). There was no difference observed in maximal HR and blood lactate concentration between the GXTs in load and unloaded conditions. This study indicates that no matter the load % used during the GXT, [Formula: see text], but not total exercise time, remains the same in young males and females.

SUBMITTER: Wang Z

PROVIDER: S-EPMC7850508 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:We analysed the importance of systemic and peripheral arteriovenous O2 difference ( a-v¯O2 difference and a-vf O2 difference, respectively) and O2 extraction fraction for maximal oxygen uptake ( V˙O2max ). Fick law of diffusion and the Piiper and Scheid model were applied to investigate whether diffusion versus perfusion limitations vary with V˙O2max . Articles (n = 17) publishing individual data (n = 154) on V˙O2max , maximal cardiac output ( Q˙max ; indicator-dilution or the Fick method), a-v¯O2 difference (catheters or the Fick equation) and systemic O2 extraction fraction were identified. For the peripheral responses, group-mean data (articles: n = 27; subjects: n = 234) on leg blood flow (LBF; thermodilution), a-vf O2 difference and O2 extraction fraction (arterial and femoral venous catheters) were obtained. Q˙max and two-LBF increased linearly by 4.9-6.0 L · min-1 per 1 L · min-1 increase in V˙O2max (R2 = .73 and R2 = .67, respectively; both P < .001). The a-v¯O2 difference increased from 118-168 mL · L-1 from a V˙O2max of 2-4.5 L · min-1 followed by a reduction (second-order polynomial: R2 = .27). After accounting for a hypoxemia-induced decrease in arterial O2 content with increasing V˙O2max (R2 = .17; P < .001), systemic O2 extraction fraction increased up to ~90% ( V˙O2max : 4.5 L · min-1 ) with no further change (exponential decay model: R2 = .42). Likewise, leg O2 extraction fraction increased with V˙O2max to approach a maximal value of ~90-95% (R2 = .83). Muscle O2 diffusing capacity and the equilibration index Y increased linearly with V˙O2max (R2 = .77 and R2 = .31, respectively; both P < .01), reflecting decreasing O2 diffusional limitations and accentuating O2 delivery limitations. In conclusion, although O2 delivery is the main limiting factor to V˙O2max , enhanced O2 extraction fraction (≥90%) contributes to the remarkably high V˙O2max in endurance-trained individuals.

Project description:IntroductionThe single-leg heel raise test (SLHR) is commonly used in clinical settings to approximate plantar flexor strength, yet this is neither validated nor supported physiologically. The purposes of this study were to: determine (1) associations between SLHR repetitions, maximal plantar flexor strength, and reductions in strength; and (2) whether sex differences exist in performance of the SLHR.MethodsTwenty-eight young, healthy participants (14 males,14 females, 19-30 years) performed repeated single-leg heel raises to task failure. Pre- and post-task measures included maximal voluntary isometric contractions (MVIC), and voluntary activation and contractile properties of the plantar flexor muscles, assessed using peripheral electrical stimulation of the tibial nerve. Surface electromyography was recorded for the medial and lateral gastrocnemius, soleus, and anterior tibialis muscles.ResultsThe SLHR resulted in 20.5% reductions in MVIC torque (p<0.001). However, the number of SLHR repetitions was not correlated with either the baseline MVIC (maximal strength; p = 0.979) or the reduction in MVIC following the SLHR (p = 0.23). There were no sex differences in either the number of SLHR repetitions (p = 0.14), baseline MVIC torque (p = 0.198), or the reduction of MVIC (p = 0.14). MVIC decline was positively associated with the reduction in voluntary activation (r = 0.841, p<0.001), but was not associated with the change in twitch amplitude (p = 0.597).ConclusionsThe SLHR was similar in young males and females yet was a poor predictor of maximal plantar flexor strength but evaluates performance fatigability of the lower extremity specific to dynamic contractions. The reduction in maximal strength at task failure was explained by reduced neural drive to the plantar flexor muscles in both males and females.Impact statementSLHR performance is not a clinical assessment of plantar flexor strength but assesses dynamic lower extremity fatigability that is similar in males and females. Alternate clinical measures for maximal plantar flexion strength need to be developed.

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Graded exercise test with or without load carriage similarly measures maximal oxygen uptake in young males and females.

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