Application and performance of heart-rate-based methods to estimate oxygen consumption at different exercise intensities in postmenopausal women

PURPOSE

Heart rate (HR) is a widespread method to estimate oxygen consumption ( V ˙ O2), exercise intensity, volume, and energy expenditure. Still, accuracy depends on lab tests or using indexes like HRnet and HRindex. This study addresses HR indexes' applicability in postmenopausal women (PMW), who constitute over 50% of the aging population and may have unique characteristics (e.g., heart size) affecting HR use.

METHODS

Fourteen PMW underwent a cycling ramp incremental test to establish the relationships between V ˙ O2 (in MET) and absolute HR, HRnet, and HRindex. In a second group of ten PMW, population-specific and general equations were tested to predict MET and energy expenditure during six constant work exercises at various intensities. Pulmonary gas exchange and HR were continuously measured using a metabolic cart. Correlations, Bland-Altman analysis, and two-way RM-ANOVA were used to compare estimated and measured values.

RESULTS

Strong linear relationships between the three HR indexes and MET were found in Group 1. In Group 2, population-specific equations showed medium-to-high correlations, precision, and no significant biases when estimating MET and energy expenditure. HRnet and HRindex outperformed absolute HR in accuracy. General HR equations had similar correlations but exhibited larger biases and imprecision. Statistical differences between measured and estimated values were observed at all intensities with general equations.

CONCLUSION

This investigation confirms the suitability of HR for estimating aerobic metabolism in one of the most significant aging populations. However, it emphasizes the importance of considering individual variability and developing population-specific models when utilizing HR to infer metabolism.

Effect of acute heat exposure on the determination of critical power and W' in women and men

The goal of this study was to investigate to what extent acute heat exposure would affect the parameters of the power-duration relationship, i.e. CP and W', using multiple constant workload tests to task failure, in women and men. Twenty four young physically active participants (12 men, 12 women) performed 3-5 constant load tests to determine CP and W', both in temperate (TEMP; 18°C) and hot (HOT; 36°C) environmental conditions. A repeated-measures ANOVA was executed to find differences between TEMP and HOT, and between women and men. In HOT, CP was reduced by 6.5% (227 ± 50 vs. 212 ± 47 W), while W' increased 12.4% (16.4 ± 4.4 vs. 18.5 ± 5.6 kJ). No significant two-way sex × temperature interactions were observed, indicating that the environmental conditions did not have a different effect in men compared with women. The intersection of the average curvatures in TEMP and HOT occurred at 137 s and 280 W in women, and 153 s and 397 W in men. Acute heat exposure had an impact on the parameters CP and W', i.e. CP decreased whereas W' increased. The increase in W' might be a consequence of the mathematical modelling for the used test methodology, rather than a physiological accurate value of W' in HOT. No differences induced by heat exposure were observed between women and men.

Critical power, W' and W' reconstitution in women and men

PURPOSE

The aim of this study was to compare critical power (CP) and work capacity W', and W' reconstitution (W'REC) following repeated maximal exercise between women and men.

METHODS

Twelve women ([Formula: see text]O2PEAK: 2.53 ± 0.37 L·min-1) and 12 men ([Formula: see text]O2PEAK: 4.26 ± 0.30 L·min-1) performed a minimum of 3 constant workload tests, to determine CP and W', and 1 maximal exercise repetition test with three work bouts (WB) to failure, to quantify W'REC during 2 recovery periods, i.e., W'REC1 and W'REC2. An independent samples t test was used to compare CP and W' values between women and men, and a repeated-measures ANOVA was used to compare W'REC as fraction of W' expended during the first WB, absolute W'REC, and normalized to lean body mass (LBM).

RESULTS

CP normalized to LBM was not different between women and men, respectively, 3.7 ± 0.5 vs. 4.1 ± 0.4 W·kgLBM-1, while W' normalized to LBM was lower in women 256 ± 29 vs. 305 ± 45 J·kgLBM-1. Fractional W'REC1 was higher in women than in men, respectively, 74.0 ± 12.0% vs. 56.8 ± 9.5%. Women reconstituted less W' than men in absolute terms (8.7 ± 1.2 vs. 10.9 ± 2.0 kJ) during W'REC1, while normalized to LBM no difference was observed between women and men (174 ± 23 vs. 167 ± 31 J·kgLBM-1). W'REC2 was lower than W'REC1 both in women and men.

CONCLUSION

Sex differences in W'REC (absolute women < men; fractional women > men) are eliminated when LBM is accounted for. Prediction models of W'REC might benefit from including LBM as a biological variable in the equation. This study confirms the occurrence of a slowing of W'REC during repeated maximal exercise.

Ecological monitoring of physical activity, emotions and daily life activities in schizophrenia: the DiAPAson study

BACKGROUND

Schizophrenia spectrum disorders (SSD) compromise psychosocial functioning, including daily time use, emotional expression and physical activity (PA).

OBJECTIVE

We performed a cohort study aimed at investigating: (1) the differences in PA, daily activities and emotions between patients with SSD and healthy controls (HC); (2) the strength of the association between these variables and clinical features among patients with SSD.

METHODS

Ninety-nine patients with SSD (53 residential patients, 46 outpatients) and 111 matched HC were assessed for several clinical variables, and levels of functioning by means of standardised clinical measures. Self-reported daily activities and emotions were assessed with a smartphone application for ecological momentary assessment (EMA), and PA levels were assessed with a wearable accelerometer for 7 consecutive days.FindingsPatients with SSD, especially those living in residential facilities, spent more time being sedentary, and self-reported more sedentary and self-care activities, experiencing higher levels of negative emotions compared with HC. Moreover, higher functioning levels among patients were associated with more time spent in moderate-to-vigorous activity.

CONCLUSIONS

Sedentary behaviour and negative emotions are particularly critical among patients with SSD and are associated with more impaired clinical outcomes.

CLINICAL IMPLICATIONS

Mobile-EMA and wearable sensors are useful for monitoring the daily life of patients with SSD and the level of PA. This population needs to be targeted with specific rehabilitative programmes aimed at improving their commitment to structured daily activities.

Temporal, Kinematic and Kinetic Variables Derived from a Wearable 3D Inertial Sensor to Estimate Muscle Power during the 5 Sit to Stand Test in Older Individuals: A Validation Study

The 5-Sit-to-stand test (5STS) is widely used to estimate lower limb muscle power (MP). An Inertial Measurement Unit (IMU) could be used to obtain objective, accurate and automatic measures of lower limb MP. In 62 older adults (30 F, 66 ± 6 years) we compared (paired t-test, Pearson's correlation coefficient, and Bland-Altman analysis) IMU-based estimates of total trial time (totT), mean concentric time (McT), velocity (McV), force (McF), and MP against laboratory equipment (Lab). While significantly different, Lab vs. IMU measures of totT (8.97 ± 2.44 vs. 8.86 ± 2.45 s, p = 0.003), McV (0.35 ± 0.09 vs. 0.27 ± 0.10 m∙s^-1, p < 0.001), McF (673.13 ± 146.43 vs. 653.41 ± 144.58 N, p < 0.001) and MP (233.00 ± 70.83 vs. 174.84 ± 71.16 W, p < 0.001) had a very large to extremely large correlation (r = 0.99, r = 0.93, and r = 0.97 r = 0.76 and r = 0.79, respectively, for totT, McT, McF, McV and MP). Bland-Altman analysis showed a small, significant bias and good precision for all the variables, but McT. A sensor-based 5STS evaluation appears to be a promising objective and digitalized measure of MP. This approach could offer a practical alternative to the gold standard methods used to measure MP.

Easy Prediction of the Maximal Lactate Steady-State in Young and Older Men and Women

Maximal Lactate steady-state (MLSS) demarcates sustainable from unsustainable exercise and is used for evaluation/monitoring of exercise capacity. Still, its determination is physically challenging and time-consuming. This investigation aimed at validating a simple, submaximal approach based on blood lactate accumulation ([Δlactate]) at the third minute of cycling in a large cohort of men and women of different ages. 68 healthy adults (40♂, 28♀, 43 ± 17 years (range 19-78), VO_2max 45 ± 11 ml^-1·kg^-1·min^-1 (25-68)) performed 3-5 constant power output (PO) trials with a target duration of 30 minutes to determine the PO corresponding to MLSS. During each trial, [Δlactate] was calculated as the difference between the third minute and baseline. A multiple linear regression was computed to estimate MLSS based on [Δlactate], subjects` gender, age and the trial PO. The estimated MLSS was compared to the measured value by paired t-test, correlation, and Bland-Altman analysis. The group mean value of estimated MLSS was 180 ± 51 W, not significantly different from (p = 0.98) and highly correlated with (R² = 0.89) measured MLSS (180 ± 54 watts). The bias between values was 0.17 watts, and imprecision 18.2 watts. This simple, submaximal, time- and cost-efficient test accurately and precisely predicts MLSS across different samples of healthy individuals (adjusted R² = 0.88) and offers a practical and valid alternative to the traditional MLSS determination.

Effect of recovery time on [Formula: see text]-ON kinetics in humans at the onset of moderate-intensity cycling exercise

PURPOSE

τ of the primary phase of [Formula: see text] kinetics during square-wave, moderate-intensity exercise mirrors that of PCr splitting (τPCr). Pre-exercise [PCr] and the absolute variations of PCr (∆[PCr]) occurring during transient have been suggested to control τPCr and, in turn, to modulate [Formula: see text] kinetics. In addition, [Formula: see text] kinetics may be slower when exercise initiates from a raised metabolic level, i.e., from a less-favorable energetic state. We verified the hypothesis that: (i) pre-exercise [PCr], (ii) pre-exercise metabolic rate, or (iii) ∆[PCr] may affect the kinetics of muscular oxidative metabolism and, therefore, τ.

METHODS

To this aim, seven active males (23.0 yy ± 2.3; 1.76 m ± 0.06, [Formula: see text]: 3.32 L min^-1 ± 0.67) performed three repetitions of series consisting of six 6-min step exercise transitions of identical workload interspersed with different times of recovery: 30, 60, 90, 120, 300 s.

RESULTS

Mono-exponential fitting was applied to breath-by-breath [Formula: see text], so that τ was determined. τ decays as a first-order exponential function of the time of recovery (τ = 109.5 × e^(-t/14.0) + 18.9 r² = 0.32) and linearly decreased as a function of the estimated pre-exercise [PCr] (τ = - 1.07 [PCr] + 44.9, r² = 0.513, P < 0.01); it was unaffected by the estimated ∆[PCr].

CONCLUSIONS

Our results in vivo do not confirm the positive linear relationship between τ and pre-exercise [PCr] and ∆[PCr]. Instead, [Formula: see text] kinetics seems to be influenced by the pre-exercise metabolic rate and the altered intramuscular energetic state.

Modeling VO2 on-kinetics based on intensity-dependent Delayed Adjustment and Loss of Efficiency (DALE)

This study presents and evaluates a new mathematical model of V̇O₂ on-kinetics, with the following properties: (i) a progressively slower primary phase following the size-principle of motor unit recruitment, explaining the delayed V̇O₂ steady state seen in the heavy exercise intensity domain, and (ii) a severe-domain slow component modelled as a time-dependent decrease in efficiency. Breath-by-breath V̇O₂ measurements from eight subjects performing step cycling transitions, in the moderate, heavy and severe exercise domains, were fitted to the conventional 3-phase model and the new model. Model performance was evaluated with a residual analysis and by comparing Bayesian (BIC) and corrected Akaike (AICc) information criteria. The residual analysis showed no systematic deviations, except perhaps for the initial part of the primary phase. BIC favored the new model, being 9.3 (SD 7.1) lower than the conventional model while AICc was similar between models. Compared to the conventional 3-phase model, the proposed model distinguishes between the kinetic adaptations in the heavy and severe domains by predicting a delayed steady state V̇O₂ in the heavy and no steady state V̇O₂ in the severe domain. This allows to determine when stable oxygen costs of exercise are attainable and it also represents a first step in defining time-dependent oxygen costs when stable energy conversion efficiency is not attainable.

Performance and Anthropometrics of Classic Powerlifters: Which Characteristics Matter?

ABSTRACT

Ferrari, L, Colosio, AL, Teso, M, and Pogliaghi, S. Performance and anthropometrics of classic powerlifters: Which characteristics matter? J Strength Cond Res 36(4): 1003-1010, 2022-The purpose of this study is: (a) provide normative performance and anthropometric data of Southern European classic powerlifters of both sexes; (b) determine the possible relationships between these variables and performance; and (c) develop population-specific predictive equations for single lifts and overall powerlifting performance. During an unofficial national-level competition, we recruited 74 athletes (51 men and 23 women) and recorded their individual, anthropometric, and performance characteristics and divided them into sex and 2 performance categories based on their Wilks points. Weaker (<370 Wilks points) and stronger (>370 Wilks points) athletes of both sexes were compared by two-way analysis of variance. Simple correlation and multiple linear regression between individual/anthropometric characteristics and performance were modeled. We applied a step-forward multiple linear regression model to predict single lifts and overall performance. All parameters significantly differed between sexes (p < 0.05 for all comparisons). Stronger male athletes had a significantly larger neck (42 ± 2.8 cm; effect size [ES] = 0.59), and flexed (40.6 ± 3.3 cm; ES = 1.18) and relaxed upper-arm (37.5 ± 3.1 cm; ES = 1.34) and thigh girths (63.6 ± 7.0 cm; ES = 0.77) compared to weaker male athletes. Furthermore, stronger women had significantly larger flexed (32.6 ± 3.3 cm; ES = 0.88) and relaxed upper-arm (33 ± 1.5 cm; ES = 2.28) and chest girths (99.3 ± 9.2 cm; ES = 1.10) compared to weaker female athletes. A combination of experience, fat mass, and upper-limb and lower-limb muscle mass indexes can accurately and precisely predict overall and individual lift performance (r2 ≥ 0.83 for all the predictions). This is the first study to provide normative performance and anthropometric data in Southern European male and female powerlifters.

An Intensity-dependent Slow Component of HR Interferes with Accurate Exercise Implementation in Postmenopausal Women

Heart rate (HR) targets are commonly used to administer exercise intensity in sport and clinical practice. However, as exercise protracts, a time-dependent dissociation between HR and metabolism can lead to a misprescription of the intensity ingredient of the exercise dose.

Repeated passive mobilization to stimulate vascular function in individuals of advanced age who are chronically bedridden. A randomized controlled trial

BACKGROUND

Vascular dysfunction and associated disorders are major side effects of chronic bed rest, yet passive mobilization as a potential treatment has only been theorized so far. This study investigated the effects of passive mobilization treatment on vascular function in older, chronically bedridden people.

METHODS

The study sample was 45 chronically bedridden people of advanced age (mean age 87 years; 56% female; mean bed rest 4 years) randomly assigned to a treatment (n=23) or a control group (CTRL, n=22). The treatment group received passive mobilization twice daily (30 min, 5 times/week) for 4 weeks. A kinesiologist performed passive mobilization by passive knee flexion/extension at 1 Hz in one leg (treated leg, T-leg vs ctrl-leg). The CTRL group received routine treatment. The primary outcome was changes in peak blood flow (∆Peak) as measured with the single passive leg movement test (sPLM) at the common femoral artery.

RESULTS

∆Peak was increased in both legs in the Treatment group (+90.9 ml/min, p<0.001, in T-leg and +25.7 ml/min, p=0.039 in ctrl-leg). No difference in peak blood flow after routine treatment was found in the CTRL group.

CONCLUSION

Improvement in vascular function after 4 weeks of passive mobilization was recorded in the treatment group. Passive mobilization may be advantageously included in standard clinical practice as an effective strategy to treat vascular dysfunction in persons with severely limited mobility.

Metabolic instability vs fibre recruitment contribution to the [Formula: see text] slow component in different exercise intensity domains

This study focused on the steady-state phase of exercise to evaluate the relative contribution of metabolic instability (measured with NIRS and haematochemical markers) and muscle activation (measured with EMG) to the oxygen consumption (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{V}O_2}$$\end{document}V˙O2) slow component (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{V}O_2}{_s}{_c}$$\end{document}V˙O2sc) in different intensity domains. We hypothesized that (i) after the transient phase, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{V}O_2}$$\end{document}V˙O2, metabolic instability and muscle activation tend to increase differently over time depending on the relative exercise intensity and (ii) the increase in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{V}O_2}{_s}{_c}$$\end{document}V˙O2sc is explained by a combination of metabolic instability and muscle activation. Eight active men performed a constant work rate trial of 9 min in the moderate, heavy and severe intensity domains. \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{V}O_2}$$\end{document}V˙O2, root mean square by EMG (RMS), deoxyhaemoglobin by NIRS ([HHb]) and haematic markers of metabolic stability (i.e. [La⁻], pH, HCO₃⁻) were measured. The physiological responses in different intensity domains were compared by two-way RM-ANOVA. The relationships between the increases of [HHb] and RMS with \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{V}O_2}$$\end{document}V˙O2 after the third min were compared by simple and multiple linear regressions. We found domain-dependent dynamics over time of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{V}O_2}$$\end{document}V˙O2, [HHb], RMS and the haematic markers of metabolic instability. After the transient phase, the rises in [HHb] and RMS showed medium–high correlations with the rise in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{V}O_2}$$\end{document}V˙O2 ([HHb] r = 0.68, p < 0.001; RMS r = 0.59, p = 0.002). Moreover, the multiple linear regression showed that both metabolic instability and muscle activation concurred to the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{V}O_2}{_s}{_c}$$\end{document}V˙O2sc (r = 0.75, [HHb] p = 0.005, RMS p = 0.042) with metabolic instability possibly having about threefold the relative weight compared to recruitment. Seventy-five percent of the dynamics of the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{V}O_2}{_s}{_c}$$\end{document}V˙O2sc was explained by [HHb] and RMS.

Ramp vs. step tests: valid alternatives to determine the maximal lactate steady-state intensity?

PURPOSE

The aims of this study were (1) to investigate if the respiratory compensation point (RCP) as derived from ramp incremental (RI) exercise could accurately predict the power output (PO) at the maximal lactate steady state (MLSS), and (2) to compare its accuracy with the second lactate threshold (LT₂) obtained from step incremental (SI) exercise.

METHODS

Nineteen participants performed a RI test (30 W·min^-1) to determine RCP, a SI test (30 or 40 W·3 min^-1) to determine LT₂, and two or more constant work rate (CWR) tests to determine MLSS. For each participant, the [Formula: see text]O₂/PO relationship for RI and CWR exercise was established. The ramp-identified PO at RCP was corrected by accounting for the gap between these relationships using the individually determined [Formula: see text] O₂/PO regression above GET (RCP_corr-1) or using a fixed regression slope (RCP_corr-2). LT₂ was determined using four methods: D_max, modified D_max (ModD_max), 4-mM threshold (LT_4mM) and an expert-determined LT₂ (LT_2-expert).

RESULTS

RCP_corr-1 (235 ± 69 W), RCP_corr-2 (228 ± 58 W) and LT_2-expert (227 ± 61 W) were not different from MLSS (225 ± 60 W). D_max (203 ± 53 W) underestimated MLSS, while RCP (280 ± 60 W), ModD_max (235 ± 67 W) and LT_4mM (234 ± 68 W) overestimated MLSS. The [Formula: see text]O₂ at RCP (3.13 ± 0.79L·min^-1) and LT_2-expert (2.99 ± 0.19L·min^-1) did not differ from MLSS (3.05 ± 0.72 L·min^-1).

CONCLUSION

This study demonstrated that RCP as derived from RI exercise and LT₂ as derived from SI exercise can be equally accurate to determine the PO associated with MLSS. Although these results confirmed the suitability of RI and SI tests for this purpose, they also highlighted the importance of an appropriate threshold method selection and the eye of the expert.

A "Step-Ramp-Step" Protocol to Identify the Maximal Metabolic Steady State

The oxygen uptake (V[Combining Dot Above]O2) at the respiratory compensation point (RCP) closely identifies with the maximal metabolic steady state. However, the power output (PO) at RCP cannot be determined from contemporary ramp-incremental exercise protocols.

PURPOSE

This study aimed to test the efficacy of a "step-ramp-step" (SRS) cycling protocol for estimating the PO at RCP and the validity of RCP as a maximal metabolic steady-state surrogate.

METHODS

Ten heathy volunteers (5 women; age: 30 ± 7 yr; V[Combining Dot Above]O2max: 54 ± 6 mL·kg·min) performed in the following series: a moderate step transition to 100 W (MOD), ramp (30 W·min), and after 30 min of recovery, step transition to ~50% POpeak (HVY). Ventilatory and gas exchange data from the ramp were used to identify the V[Combining Dot Above]O2 at lactate threshold (LT) and RCP. The PO at LT was determined by the linear regression of the V[Combining Dot Above]O2 versus PO relationship after adjusting ramp data by the difference between the ramp PO at the steady-state V[Combining Dot Above]O2 from MOD and 100 W. Linear regression between the V[Combining Dot Above]O2-PO values associated with LT and HVY provided, by extrapolation, the PO at RCP. Participants then performed 30-min constant-power tests at the SRS-estimated RCP and 5% above this PO.

RESULTS

All participants completed 30 min of constant-power exercise at the SRS-estimated RCP achieving steady-state V[Combining Dot Above]O2 of 3176 ± 595 mL·min that was not different (P = 0.80) from the ramp-identified RCP (3095 ± 570 mL·min) and highly consistent within participants (bias = -26 mL·min, r = 0.97, coefficient of variation = 2.3% ± 2.8%). At 5% above the SRS-estimated RCP, four participants could not complete 30 min and all, but two exhibited non-steady-state responses in blood lactate and V[Combining Dot Above]O2.

CONCLUSIONS

In healthy individuals cycling at their preferred cadence, the SRS protocol and the RCP are capable of accurately predicting the PO associated with maximal metabolic steady state.

Full characterisation of knee extensors' function in ageing: effect of sex and obesity

BACKGROUND/OBJECTIVES

Muscle function is a marker of current and prospective health/independence throughout life. The effects of sex and obesity (OB) on the loss of muscle function in ageing remain unresolved, with important implications for the diagnosis/monitoring of sarcopenia. To characterise in vivo knee extensors' function, we compared muscles torque and power with isometric and isokinetic tests in older men (M) and women (W), with normal range (NW) of body mass index (BMI) and OB.

SUBJECTS/METHODS

In 70 sedentary older M and W (69 ± 5 years), NW and OB (i.e. BMI < 30 kg m^-2 and ≥30 kg m^-2, respectively) we tested the right knee's extensor: (i) isometric torque at 30°, 60°, 75° and 90° knee angles, and (ii) isokinetic concentric torque at 60, 90, 150, 180 and 210° s^-1 angular speeds. Maximal isometric T-angle, maximal isokinetic knee-extensor torque-velocity, theoretical maximal shortening velocity, maximal power, optimal torque and velocity were determined in absolute units, normalised by body mass (BM) and right leg lean mass (LLM_R) and compared over sex, BMI categories and angle or angular speeds by three-way ANOVA.

RESULTS

In absolute units, relative to BM and LLM_R, sex differences were found in favour of M for all parameters of muscle function (main effect for sex, p < 0.05). OB did not affect either absolute or relative to LLM_R isometric and isokinetic muscle function (main effect for BMI, p > 0.05); however, muscle function indices, when adjusted for BM, were lower in both M and W with OB compared to NW counterparts (p < 0.05).

CONCLUSIONS

We confirmed sex differences in absolute, relative to BM and LLM_R muscle function in favour of men. While overall muscle function and muscle contractile quality is conserved in individuals with class I OB, muscle function normalised for BM, which defines the ability to perform independently and safely the activities of daily living, is impaired in comparison with physiological ageing.

Testing the Performance of an Innovative Markerless Technique for Quantitative and Qualitative Gait Analysis

Gait abnormalities such as high stride and step frequency/cadence (SF-stride/second, CAD-step/second), stride variability (SV) and low harmony may increase the risk of injuries and be a sentinel of medical conditions. This research aims to present a new markerless video-based technology for quantitative and qualitative gait analysis. 86 healthy individuals (mead age 32 years) performed a 90 s test on treadmill at self-selected walking speed. We measured SF and CAD by a photoelectric sensors system; then, we calculated average ± standard deviation (SD) and within-subject coefficient of variation (CV) of SF as an index of SV. We also recorded a 60 fps video of the patient. With a custom-designed web-based video analysis software, we performed a spectral analysis of the brightness over time for each pixel of the image, that reinstituted the frequency contents of the videos. The two main frequency contents (F1 and F2) from this analysis should reflect the forcing/dominant variables, i.e., SF and CAD. Then, a harmony index (HI) was calculated, that should reflect the proportion of the pixels of the image that move consistently with F1 or its supraharmonics. The higher the HI value, the less variable the gait. The correspondence SF-F1 and CAD-F2 was evaluated with both paired t-Test and correlation and the relationship between SV and HI with correlation. SF and CAD were not significantly different from and highly correlated with F1 (0.893 ± 0.080 Hz vs. 0.895 ± 0.084 Hz, p < 0.001, r² = 0.99) and F2 (1.787 ± 0.163 Hz vs. 1.791 ± 0.165 Hz, p < 0.001, r² = 0.97). The SV was 1.84% ± 0.66% and it was significantly and moderately correlated with HI (0.082 ± 0.028, p < 0.001, r² = 0.13). The innovative video-based technique of global, markerless gait analysis proposed in our study accurately identifies the main frequency contents and the variability of gait in healthy individuals, thus providing a time-efficient, low-cost means to quantitatively and qualitatively study human locomotion.

Bioenergetics of the VO2 slow component between exercise intensity domains

During heavy and severe constant-load exercise, VO2 displays a slow component (VO2sc) typically interpreted as a loss of efficiency of locomotion. In the ongoing debate on the underpinnings of the VO2sc, recent studies suggested that VO2sc could be attributed to a prolonged shift in energetic sources rather than loss of efficiency. We tested the hypothesis that the total cost of cycling, accounting for aerobic and anaerobic energy sources, is affected by time during metabolic transitions in different intensity domains. Eight active men performed 3 constant load trials of 3, 6, and 9 min in the moderate, heavy, and severe domains (i.e., respectively below, between, and above the two ventilatory thresholds). VO2, VO2 of ventilation and lactate accumulation ([La-]) were quantified to calculate the adjusted oxygen cost of exercise (AdjO2Eq, i.e., measured VO2 - VO2 of ventilation + VO2 equivalent of [La-]) for the 0-3, 3-6, and 6-9 time segments at each intensity, and compared by a two-way RM-ANOVA (time × intensity). After the transient phase, AdjO2Eq was unaffected by time in moderate (ml*3 min-1 at 0-3, 0-6, 0-9 min: 2126 ± 939 < 2687 ± 1036, 2731 ± 1035) and heavy (4278 ± 1074 < 5121 ± 1268, 5225 ± 1123) while a significant effect of time was detected in the severe only (5863 ± 1413 < 7061 ± 1516 < 7372 ± 1443). The emergence of the VO2sc was explained by a prolonged shift between aerobic and anaerobic energy sources in heavy (VO2 - VO2 of ventilation: ml*3 min-1 at 0-3, 0-6, 0-9 min: 3769 ± 1128 < 4938 ± 1256, 5091 ± 1123, [La-]: 452 ± 254 < 128 ± 169, 79 ± 135), while a prolonged metabolic shift and a true loss of efficiency explained the emergence of the VO2sc in severe.

Time-course of running treadmill adaptation in novice treadmill runners

Studies on running biomechanics and energetics are usually conducted on a treadmill. To ensure that locomotion on a treadmill is comparable to locomotion overground, participants need to be expert in the use of the device. This study aimed to identify the number and duration of sessions needed to obtain stable measurements for spatiotemporal and metabolic parameters in unexperienced treadmill runners. Fourteen male recreational runners performed three 15-min treadmill running trials in different days at a submaximal speed. Spatiotemporal and metabolic parameters were registered at minutes: 5, 10, 15 and their within-trial and between-trial changes were analysed using a two-way repeated measures ANOVA and Bonferroni post-hoc test. Within-trial differences were found in step frequency (decreased over time), Step Length and Contact Time (increased), reaching stability at different time points. Ventilator parameters increased, reaching stability after 5-10 min, while heart rate increased progressively over time. The only between-trial differences were an increase in step length and a decrease in step frequency at min 1, between trials 1 and 3. In conclusion, at least three running trials of 15 min are required to familiarize with the device. The last 5 min of the third trial can be regarded as stable measurements.

DAily time use, Physical Activity, quality of care and interpersonal relationships in patients with Schizophrenia spectrum disorders (DiAPASon): an Italian multicentre study

BACKGROUND

Schizophrenia spectrum disorders (SSD) are ranked among the leading causes of disabilities worldwide. Many people with SSD spend most of their daily time being inactive, and this is related to the severity of negative symptoms. Here, we present the 3-year DiAPAson project aimed at (1) evaluating the daily time use among patients with SSD living in Residential Facilities (RFs) compared to outpatients with SSD and to the general population (Study 1); (2) evaluating the quality of staff-patient relationships, its association with specific patient outcomes and the quality of care provided in RFs (Study 2); and (3) assessing daily activity patterns in residential patients, outpatients with SSD and healthy controls using real-time methodologies (Study 3).

METHODS

Study 1 will include 300 patients with SSD living in RFs and 300 outpatients; data obtained in these clinical populations will be compared with normative data obtained by the National Institute of Statistics (ISTAT) in the national survey on daily time use. Time use assessments will consist of daily diaries asking participants to retrospectively report time spent in different activities. In Study 2, a series of questionnaires will be administered to 300 residential patients (recruited for Study 1) to evaluate the quality of care and staff-patient relationships, level of well-being and burnout of RFs' staff, and quality of RFs using a European standardized questionnaire (QuIRC-SA). In Study 3, the daily time use will be evaluated in a subgroup of 50 residential patients, 50 outpatients and 50 healthy controls using the Experience Sampling Method approach (participants will complete a brief questionnaire -about time use, mood and perceived energy- on a smartphone 8 times a day for 1 week) to compare retrospective and real-time reports. Moreover, their level of physical activity, sleep patterns, and energy expenditure will be monitored through a multi-sensor device.

DISCUSSION

This project is highly innovative because it combines different types of assessments (i.e., retrospective and real-time reports; multi-sensor monitoring) to trace an accurate picture of daily time use and levels of physical activity that will help identify the best therapeutic options promoting daily activities and physical exercise in patients with SSD.

TRIAL REGISTRATION

ISRCTN registry ID ISRCTN21141466.

Heart rate-index estimates aerobic metabolism in professional soccer players

OBJECTIVES

This study aimed at proposing a new heart rate (HR) method to track aerobic metabolism in soccer by: (i) validating a recently developed HR index (HR_index) in professional soccer players, (ii) comparing HR_index vs the most common HR parameters and (iii) testing the agreement between measured and estimated VO₂ values using HR_index.

DESIGN

cross-sectional.

METHODS

184 professional soccer players performed a step incremental running test on a treadmill while VO₂ and HR were recorded. HR_index was calculated (actual HR/resting HR) and its relationship with VO₂ was compared with the relationships with the metabolism of actual HR, net HR, and % of HR reserve. Finally, HR_index was used to predict VO₂=((HR_index·6)-5)·3.5) and measured and estimated VO₂ were compared by 2W RM-ANOVA and Bland-Altman analysis.

RESULTS

HR_index/VO₂ relationship explained 85% of the variability in data, showing a higher performance than actual HR (77%) and similar values to the other parameters. Measured and estimated VO₂ were not significantly different ≤14kmh^-1, whereas at speeds ≥14kmh^-1 measured VO₂ was higher than estimated VO₂. Finally, measured and estimated VO₂ were highly correlated (R²=0.85, p=0.000), and showed no significant bias (bias=-1.03, z=-0.69, precision=3.75mlkgmin^-1).

CONCLUSIONS

We validated the HR_index/VO₂ relationship in professional soccer players. HR_index showed better agreement with metabolism than actual HR and similar agreement to the other HR parameters. HR_index allowed to estimate VO₂, but at very high-intensity HR_index underestimated VO₂. Future studies should test this in real game conditions. HR_index could offer a time-efficient and easy-to-use "field" method to monitor aerobic metabolism in soccer.

Monitoring exercise intensity in diabetes: applicability of "heart rate-index" to estimate oxygen consumption during aerobic and resistance training

PURPOSE

Accurate quantification and monitoring of exercise "dose", described by oxygen consumption (VO₂), is necessary for exercise prescription and individualization. However, due to the complexity and elevated cost of direct, gold-standard methods, this is rarely done outside research laboratories. Heart rate-index (HR_index) is a new simple method to estimate VO₂ in healthy and clinical populations. We tested the performance of HR_index to estimate VO₂ in diabetic patients during aerobic (AT) and isotonic training (IT).

METHODS

Data from 12 males (age: 64 ± 5 years; BMI: 26 ± 12) with type 2 diabetes were analysed. VO₂ and heart rate were measured during one AT and one IT session. Furthermore, VO₂ was indirectly estimated based on HR_index. Then, the correspondence between measured and estimated VO₂ was evaluated by two-way RM-ANOVA, correlation and Bland-Altman analysis.

RESULTS

Estimated average VO₂ values during AT (1292 ± 366 ml/min) were not different from (p = 0.243) and highly correlated with (r = 0.87, p < 0.001) the measured values (1369 ± 417 ml/min), with a small bias and imprecision. Conversely during IT, HR_index overestimated VO₂ compared to the actual measures (1048 ± 404 vs 667 ± 230 ml/min, p ≤ 0.001) and only a moderate correlation was found between values (r = 0.43, p ≤ 0.001), with a large bias and imprecision.

CONCLUSION

VO₂ of aerobic exercises can be accurately estimated in diabetes patients using HR_index. During isotonic exercise, this method is not recommended for monitoring metabolic intensity due to large overestimation and imprecision. In aerobic exercise, HR_index offers a simple and valid alternative to the direct VO₂ determination and may favour the applicability of time-resolved measures of exercise "dose".

The Vascular Side of Chronic Bed Rest: When a Therapeutic Approach Becomes Deleterious

The interplay between chronic constraint and advanced aging on blood flow, shear-rate, vascular function, nitric oxide (NO)-bioavailability, microcirculation, and vascular inflammation factors is still a matter of debate. Ninety-eight individuals (Young, n = 28, 23 ± 3 yrs; Old, n = 36, 85 ± 7 yrs; Bedridden, n = 34, 88 ± 6 yrs) were included in the study. The bedridden group included old individuals chronically confined to bed (3.8 ± 2.3 yrs). A blood sample was collected and analyzed for plasma nitrate, and vascular inflammatory markers. Hyperemic response (∆peak) during the single passive leg movement (sPLM) test was used to measure vascular function. Skeletal muscle total hemoglobin was measured at the vastus lateralis during the sPLM test, by means of near infrared spectroscopy (NIRS). Bedridden subjects revealed a depletion of plasma nitrates compared with Old (−23.8%) and Young (−31.1%). Blood flow was lower in the Bedridden in comparison to Old (−20.1%) and Young (−31.7%). Bedridden presented lower sPLM ∆peak compared Old (−72.5%) and the Young (−83.3%). ∆peak of NIRS total hemoglobin was lower in the Bedridden compared to that in the Young (−133%). All vascular inflammatory markers except IL-6 were significantly worse in the Bedridden compared to Old and Young. No differences were found between the Old and Young in inflammatory markers. Results of this study confirm that chronic physical constraint induces an exacerbation of vascular disfunction and differential regulation of vascular-related inflammatory markers. The mechanisms involved in these negative adaptations seems to be associated with endothelial dysfunction and consequent diminished NO-bioavailability likely caused by the reduced shear-rate consequential to long-term reduction of physical activity.

Prolonged static stretching causes acute, nonmetabolic fatigue and impairs exercise tolerance during severe-intensity cycling

We tested the hypothesis that static stretching, an acute, nonmetabolic fatiguing intervention, reduces exercise tolerance by increasing muscle activation and affecting muscle bioenergetics during cycling in the "severe" intensity domain. Ten active men (age, 24 ± 2 years; body mass, 74 ± 11 kg; height, 176 ± 8 cm) participated in identical constant-load cycling tests of equal intensity, of which 2 tests were carried out under control conditions and 2 were done after stretching. This resulted in a 5% reduction of maximal isokinetic sprinting power output. We measured (i) oxygen consumption, (ii) electromyography, (iii) deoxyhemoglobin, (iv) blood lactate concentration; (v) time to exhaustion, and (vi) perception of effort. Finally, oxygen consumption and deoxyhemoglobin kinetics were determined. Force reduction following stretching was accompanied by augmented muscle excitation at a given workload (p = 0.025) and a significant reduction in time to exhaustion (p = 0.002). The time to peak oxygen consumption was reduced by stretching (p = 0.034), suggesting an influence of the increased muscle excitation on the oxygen consumption kinetics. Moreover, stretching was associated with a mismatch between O₂ delivery and utilization during the isokinetic exercise, increased perception of effort, and blood lactate concentration; these observations are all consistent with an increased contribution of the glycolytic energy system to sustain the same absolute intensity. These results suggest a link between exercise intolerance and the decreased ability to produce force. Novelty We provided the first characterization of the effects of prolonged stretching on the metabolic response during severe cycling. Stretching reduced maximal force and augmented muscle activation, which in turn increased the metabolic response to sustain exercise.

Aerobic Interval Training Impacts Muscle and Brain Oxygenation Responses to Incremental Exercise

The purpose of the present study was to assess the effects of aerobic interval training on muscle and brain oxygenation to incremental ramp exercise. Eleven physically active subjects performed a 6-week interval training period, proceeded and followed by an incremental ramp exercise to exhaustion (25 W min^–1). Throughout the tests pulmonary gas exchange and muscle (Vastus Lateralis) and brain (prefrontal cortex) oxygenation [concentration of deoxygenated and oxygenated hemoglobin, HHb and O₂Hb, and tissue oxygenation index (TOI)] were continuously recorded. Following the training intervention V.⁢O2_peak had increased with 7.8 ± 5.0% (P < 0.001). The slope of the decrease in muscle TOI had decreased (P = 0.017) 16.6 ± 6.4% and the amplitude of muscle HHb and totHb had increased (P < 0.001) 40.4 ± 15.8 and 125.3 ± 43.1%, respectively. The amplitude of brain O₂Hb and totHb had increased (P < 0.05) 40.1 ± 18.7 and 26.8 ± 13.6%, respectively. The training intervention shifted breakpoints in muscle HHb, totHb and TOI, and brain O₂Hb, HHb, totHb and TOI to a higher absolute work rate and V.⁢O2 (P < 0.05). The relative (in %) change in V.⁢O2_peak was significantly correlated to relative (in %) change slope of muscle TOI (r = 0.69, P = 0.011) and amplitude of muscle HHb (r = 0.72, P = 0.003) and totHb (r = 0.52, P = 0.021), but not to changes in brain oxygenation. These results indicate that interval training affects both muscle and brain oxygenation, coinciding with an increase in aerobic fitness (i.e., V.⁢O2_peak). The relation between the change in V.⁢O2_peak and muscle but not brain oxygenation suggests that brain oxygenation per se is not a primary factor limiting exercise tolerance during incremental exercise.

Noninvasive and in vivo assessment of upper and lower limb skeletal muscle oxidative metabolism activity and microvascular responses to glucose ingestion in humans

This study investigated changes in muscle oxidative metabolism and microvascular responsiveness induced by glucose ingestion in the upper and lower limbs using near-infrared spectroscopy (NIRS). Fourteen individuals (aged 27 ± 1.4 years) underwent 5 vascular occlusion tests (VOT) (pre-intervention (Pre), 30 min, 60 min, 90 min, and 120 min after glucose challenge). NIRS-derived oxygen saturation (StO2) was measured on the forearm and leg muscle at each VOT. Muscle oxidative metabolism was determined by the StO2 downslope during cuff inflation (deoxygenation slope); microvascular responsiveness was estimated by the StO2 upslope (reperfusion slope) following cuff deflation. There was a significant increase in arm (p < 0.05; 1-β = 0.860) and leg (p < 0.05; 1-β = 1.000) oxidative metabolism activity as represented by the faster deoxygenation slope at 60, 90, and 120 min (0.08 ± 0.03, 0.08 ± 0.03, 0.08 ± 0.02%·s–1, respectively) (leg) and at 90 min (0.16 ± 0.08%·s−1) (arm) observed after glucose ingestion when compared with their respective Pre values (leg = 0.06 ± 0.02; arm = 0.11 ± 0.04%·s−1). There was a significant increase in arm (p < 0.05; 1-β = 0.880) and leg (p < 0.05; 1-β = 0.983) reperfusion slope at 60 min (arm = 3.63 ± 2.1%·s−1; leg = 1.56 ± 0.6%·s−1), 90 min (arm = 3.91 ± 2.1%·s−1; leg = 1.60 ± 0.6%·s−1), and 120 min (arm = 3.91 ± 1.6%·s−1; leg = 1.54 ± 0.6%·s−1) when compared with their Pre values (arm = 2.79 ± 1.7%·s−1; leg = 1.26 ± 0.5%·s−1). Our findings showed that NIRS–VOT technique is capable of detecting postprandial changes in muscle oxidative metabolism activity and microvascular reactivity in the upper and lower limb.

Novelty NIRS-VOT is a promising noninvasive clinical approach that may help in the early, limb-specific detection of impairments in glucose oxidation and microvascular function.

Respiratory and muscular response to acute non-metabolic fatigue during ramp incremental cycling

We tested the hypothesis that acute, non-metabolic fatigue, by reducing maximal power output and possibly increasing muscle recruitment at a given exercise intensity, will reduce indexes of exercise tolerance during incremental cycling. Ten subjects performed three ramp incremental tests respectively after static stretching (STRC), dropjumps (DJ) or control (CTRL). Fatigue was assessed as reduction in maximal power output (_sprintPO) during isokinetic sprints. During the ramps we measured: oxygen consumption (VO₂), power output (PO), and surface electromyography. _sprintPO was reduced after STRC and DJ (p = 0.007) yet not after CTRL. During the ramps, the interventions augmented muscle excitation vs CTRL (p ≤ 0.001). Peak PO and VO₂ were reduced after STRC (302 ± 39W p = 0.033, 3365 ± 465 ml/min p = 0.015) and DJ (300 ± 37W p = 0.023, 3413 ± 476 ml/min p = 0.094) vs CTRL (314 ± 41W, 3505 ± 486 ml/min). Interventions were associated with early occurrence of the ventilatory thresholds and increased VO₂ vs CTRL (p = 0.029). The physiological response after acute non-metabolic fatigue suggests a link between exercise intolerance and the decreased ability to produce force.

Heart Rate-Index Estimates Oxygen Uptake, Energy Expenditure and Aerobic Fitness in Rugby Players

The purpose of the study was to verify the suitability of heart rate-index (HR_index) in predicting submaximal oxygen consumption (VO₂), energy expenditure (EE) and maximal oxygen consumption (VO_2max) during treadmill running in rugby players. Fifteen professional rugby players (99.8 ± 12.7 kg, 1.85 ± 0.09 m) performed a running incremental test while VO_{2 (}breath-by-breath₎ and heart rate (HR) were measured. HR_index was calculated (actual HR/resting HR) to predict submaximal and maximal VO₂ ({[(HR_index x 6)-5.0] x (3.5 body weight)}) and EE. Measured and predicted VO₂ and EE were compared by two-way RM-ANOVA (method, speed), correlation and Bland-Altman analysis. Measured and predicted VO_2max were compared by paired t-test, correlation and Bland-Altman analysis. Submaximal VO₂ and EE significantly increased (baseline VO₂: 8.1 ± 1.6 ml·kg^-1·min^-1VO_2max: 46.8 ± 4.3 ml·kg^-1·min^-1, baseline EE: 0.03 ± 0.01 kcal·kg^-1·min^-1, peak EE: 0.23 ± 0.03 kcal·kg^-1·min^-1) as a function of speed (p < 0.001 and p < 0.001 for VO₂ and EE respectively) yet measured and predicted values at equal treadmill speeds were not significantly different (p = 0.17; p = 0.16) and highly correlated (r = 0.95; r = 0.94). The Bland-Altman analysis confirmed a non-significant bias between measured and estimated VO₂ (measured: 40.3 ± 10.7, estimated: 40.7 ± 10.1 ml·kg^-1·min^-1, bias = 1.35 ml·kg^-1·min^-1, z = 1.12, precision = 3.39 ml·kg^-1·min^-1) and EE (measured: 20.0 ± 0.05 kcal·kg^-1·min^-1, estimated: 20.0 ± 0.05 kcal·kg^-1·min^-1, bias = 0.00 kcal·kg^-1·min^-1, z = 0.04, precision = 0.02 kcal·kg^-1·min^-1). Estimated and predicted VO_2max were not statistically different (p = 0.91), highly correlated (r = 0.96), and showed a non-significant bias (bias = 0.17, z = 0.22, precision = 1.29 ml·kg^-1·min^-1). HR_index is a valid field method to track VO₂, EE and VO_2max during running in rugby players.

Effect of Endurance and Strength Training on the Slow Component of O 2 Kinetics in Elderly Humans

We compared the effects of 8 weeks of high intensity, aerobic interval training (HIT) and isoinertial resistance training (IRT) on: (i) O₂ kinetics during heavy (HiEx) intensity exercise and; (ii) work economy during moderate (ModEx) intensity exercise in 12 healthy elderly men (69.3 ± 4.2 years). Breath-by-breath O₂ and muscle deoxygenation ([HHb] by means of NIRS) were measured in HiEx and ModEx at identical workloads before and after trainings. In HiEx, O₂ and HHb responses were modeled as tri-exponential and mono-exponential increasing functions, respectively. A two-way ANOVA for repeated measures analysis was made; Effect size (η²) was also evaluated. After HIT the amplitude and the time delay of the slow component of O₂ uptake (O_2sc) during HiEx were smaller (−32%; P = 0.045) and longer (+19.5%; P = 0.001), respectively. At Post IRT: (i) during ModEx, gain was lower (−5%; P = 0.050); (ii) during HiEx, τ₂ (+14.4%; P = 0.050), d₃ (+8.6%; P = 0.050), and τ₃ (+17.2%; P = 0.050) were longer than at Pre IRT. After HIT, the decrease of the O_2sc amplitude was likely induced by the beneficial effects of training on a more responsive O₂ delivery and consumption cascade leading to a better muscle metabolic stability. IRT training was able to increase exercise economy during ModEx and to reduce the amplitude and delay the onset of O_2sc during HiEx. These effects should be due to the reduction and the delayed recruitment of Type II muscle fibers. The better exercise economy and the delayed appearance of O_2sc induced by IRT suggests that strength training might be included in endurance training programs to improve exercise economy and resistance to fatigue in this population of old subjects.

Reliability of microvascular responsiveness measures derived from near-infrared spectroscopy across a variety of ischemic periods in young and older individuals

BACKGROUND

Cardiovascular disease (CVD) is associated with impairments in microvascular responsiveness. Therefore, reliably assessing microvascular function is clinically relevant. Thus, this study aimed to examine the reliability of the near-infrared spectroscopy (NIRS)-derived oxygen saturation (StO₂) reperfusion slope, a measure of microvascular responsiveness, to four different vascular occlusion tests (VOT) of different durations in young and older participants.

METHODS

Eight healthy young (29 ± 5 yr) and seven older (67 ± 4 yr) men participated in four NIRS combined with VOT (NIRS-VOT; 30 s, 1, 3, and 5 min) in the leg microvasculature on two visits separated by 1-2 weeks. Vascular responsiveness was determined by the StO₂ reperfusion slope. The coefficient of variation (CV), repeatability, reliability (ICC), and the limits of agreement (LOA) were calculated for the NIRS-derived reperfusion slopes for each occlusion duration and visit.

RESULTS

CV for the StO₂ reperfusion slope following 30 s, 1, 3 and 5 min of occlusion were 33 ± 29%, 19 ± 21%, 14 ± 12%, and 12 ± 10%, respectively. Repeatability values following 30 s, 1, 3 and 5 min occlusions were 20%, 1%, 4% and 21%, respectively. The ICC for the StO₂ reperfusion slopes for each occlusion duration were 0.29, 0.42, 0.84, and 0.88 following 30 s, 1, 3 and 5 min of occlusion, respectively. LOA values between visit 1 and 2 for occlusions were not different from zero. There were no age-related differences for all variables of the study.

CONCLUSION

NIRS-derived StO₂ reperfusion slope, has good reliability across a range of occlusion durations with the strongest reliability during longer occlusion durations.

An equation to predict the maximal lactate steady state from ramp-incremental exercise test data in cycling

OBJECTIVES

The maximal lactate steady state (MLSS) represents the highest exercise intensity at which an elevated blood lactate concentration ([Lac]_b) is stabilized above resting values. MLSS quantifies the boundary between the heavy-to-very-heavy intensity domains but its determination is not widely performed due to the number of trials required.

DESIGN

This study aimed to: (i) develop a mathematical equation capable of predicting MLSS using variables measured during a single ramp-incremental cycling test and (ii) test the accuracy of the optimized mathematical equation.

METHODS

The predictive MLSS equation was determined by stepwise backward regression analysis of twelve independent variables measured in sixty individuals who had previously performed ramp-incremental exercise and in whom MLSS was known (MLSS_obs). Next, twenty-nine different individuals were prospectively recruited to test the accuracy of the equation. These participants performed ramp-incremental exercise to exhaustion and two-to-three 30-min constant-power output cycling bouts with [Lac]_b sampled at regular intervals for determination of MLSS_obs. Predicted MLSS (MLSS_pred) and MLSS_obs in both phases of the study were compared by paired t-test, major-axis regression and Bland-Altman analysis.

RESULTS

The predictor variables of MLSS were: respiratory compensation point (Wkg^-1), peak oxygen uptake (V˙O_2peak) (mlkg^-1min^-1) and body mass (kg). MLSS_pred was highly correlated with MLSS_obs (r=0.93; p<0.01). When this equation was tested on the independent group, MLSS_pred was not different from MLSS_obs (234±43 vs. 234±44W; SEE 4.8W; r=0.99; p<0.01).

CONCLUSIONS

These data support the validity of the predictive MLSS equation. We advocate its use as a time-efficient alternative to traditional MLSS testing in cycling.

Quantification of energy expenditure of military loaded runs: what is the performance of laboratory-based equations when applied to the field environment?

Introduction

Performance during army loaded runs provides a synthetic indicator of a soldier’s capacity to move while carrying loads and thereby remain able to execute a mission. The aim of this study was to estimate and compare the energy expenditure (EE) of army loaded runs, conducted in a field environment using laboratory-based equations and HR index (HRindex).

Methods

45 Ranger recruits had HR monitored during three loaded runs (10, 15 and 20 km) in full military equipment in the field environment. EE was calculated using reference equations (EE-Eq) and estimates of oxygen consumption based on HRindex (EE-HRindex). Correspondence between EE-Eq and EE-HRindex estimates was evaluated using a two-way analysis of variance, correlation test and Bland-Altman analysis.

Results

EE-Eq relative to time and weight was significantly higher for the 10 km (0.175±0.016) compared with 15 and 20 km (0.163±0.016 and 0.160±0.013 kcal/kg/min, not different). The overall EE-Eq increased significantly with distance (1129±59, 1703±80 and 2250±115 kcal for 10, 15 and 20 km). EE-Eq was not different from and highly correlated with EE-HRindex, with a small and non-significant bias and good precision between methods.

Conclusions

Our study provides the first comprehensive data on HR and EE during long-distance loaded army runs, in full combat equipment, in actual field conditions. Equation-based estimates of EE during these heavy-intensity activities were not significantly different from and highly correlated with HR-based estimates. This corroborates the general applicability of the predictive equations in the field environment. Furthermore, our study suggests that time-resolved HR-based estimates of EE during army runs can be used to evaluate for the effects of context specificity, individual variability and fatigue in movement economy.

Measurement of a True [Formula: see text]O2max during a Ramp Incremental Test Is Not Confirmed by a Verification Phase

The accuracy of an exhaustive ramp incremental (RI) test to determine maximal oxygen uptake ([Formula: see text]O_2max) was recently questioned and the utilization of a verification phase proposed as a gold standard. This study compared the oxygen uptake ([Formula: see text]O₂) during a RI test to that obtained during a verification phase aimed to confirm attainment of [Formula: see text]O_2max. Sixty-one healthy males [31 older (O) 65 ± 5 yrs; 30 younger (Y) 25 ± 4 yrs] performed a RI test (15-20 W/min for O and 25 W/min for Y). At the end of the RI test, a 5-min recovery period was followed by a verification phase of constant load cycling to fatigue at either 85% (n = 16) or 105% (n = 45) of the peak power output obtained from the RI test. The highest [Formula: see text]O₂ after the RI test (39.8 ± 11.5 mL·kg^-1·min^-1) and the verification phase (40.1 ± 11.2 mL·kg^-1·min^-1) were not different (p = 0.33) and they were highly correlated (r = 0.99; p < 0.01). This response was not affected by age or intensity of the verification phase. The Bland-Altman analysis revealed a very small absolute bias (-0.25 mL·kg^-1·min^-1, not different from 0) and a precision of ±1.56 mL·kg^-1·min^-1 between measures. This study indicated that a verification phase does not highlight an under-estimation of [Formula: see text]O_2max derived from a RI test, in a large and heterogeneous group of healthy younger and older men naïve to laboratory testing procedures. Moreover, only minor within-individual differences were observed between the maximal [Formula: see text]O₂ elicited during the RI and the verification phase. Thus a verification phase does not add any validation of the determination of a [Formula: see text]O_2max. Therefore, the recommendation that a verification phase should become a gold standard procedure, although initially appealing, is not supported by the experimental data.

Critical power: How different protocols and models affect its determination

In cycling, critical power (CP) and work above CP (W') can be estimated through linear and nonlinear models. Despite the concept of CP representing the upper boundary of sustainable exercise, overestimations may be made as the models possess inherent limitations and the protocol design is not always appropriate.

OBJECTIVES

To measure and compare CP and W' through the exponential (CP_exp), 3-parameter hyperbolic (CP_3-hyp), 2-parameter hyperbolic (CP_2-hyp), linear (CP_linear), and linear 1/time (CP_1/time) models, using different combinations of TTE trials of different durations (approximately 1-20min).

DESIGN

Repeated measures.

METHODS

Thirteen healthy young cyclists (26±3years; 69.0±9.2kg; 174±10cm; 60.4±5.9mLkg^-1min^-1) performed five TTE trials on separate days. CP and W' were modeled using two, three, four, and/or five trials. All models were compared against a criterion method (CP_3-hyp with five trials; confirmed using the leaving-one-out cross-validation analysis) using smallest worthwhile change (SWC) and concordance correlation coefficient (CCC) analyses.

RESULTS

CP was considerably overestimated when only trials lasting less than 10min were included, independent of the mathematical model used. Following CCC analysis, a number of alternative methods were able to predict our criterion method with almost a perfect agreement. However, the application of other common approaches resulted in an overestimation of CP and underestimation of W', typically these methods only included TTE trials lasting less than 12min.

CONCLUSIONS

Estimations from CP_3-hyp were found to be the most accurate, independently of TTE range. Models that include two trials between 12 and 20min provide good agreement with the criterion method (for both CP and W').