Critical velocity during continuous and intermittent exercises in children

The W' Balance Model: Mathematical and Methodological Considerations

Since its publication in 2012, the W' balance model has become an important tool in the scientific armamentarium for understanding and predicting human physiology and performance during high-intensity intermittent exercise. Indeed, publications featuring the model are accumulating, and it has been adapted for popular use both in desktop computer software and on wrist-worn devices. Despite the model's intuitive appeal, it has achieved mixed results thus far, in part due to a lack of clarity in its basis and calculation. Purpose: This review examines the theoretical basis, assumptions, calculation methods, and the strengths and limitations of the integral and differential forms of the W' balance model. In particular, the authors emphasize that the formulations are based on distinct assumptions about the depletion and reconstitution of W' during intermittent exercise; understanding the distinctions between the 2 forms will enable practitioners to correctly implement the models and interpret their results. The authors then discuss foundational issues affecting the validity and utility of the model, followed by evaluating potential modifications and suggesting avenues for further research. Conclusions: The W' balance model has served as a valuable conceptual and computational tool. Improved versions may better predict performance and further advance the physiology of high-intensity intermittent exercise.

Heart Rate Responses during Sport-Specific High-Intensity Circuit Exercise in Child Female Gymnasts

This study examined heart rate (HR) responses during a sport-specific high-intensity circuit training session to indirectly assess cardiorespiratory stress in child athletes. Seventeen, female gymnasts, aged 9-11 years performed two 5-min 15 s sets of circuit exercise, interspersed by a 3 min rest interval. Each set included five rounds of five gymnastic exercises (7 s work, 7 s rest) executed with maximal effort. During the first circuit training set, peak heart rate (HR) was 192 ± 7 bpm and average HR was 83 ± 4% of maximum HR (HRmax), which was determined in a separate session. In the second set, peak HR and average HR were increased to 196 ± 8 bpm (p < 0.001, d = 0.55) and to 89 ± 4% HRmax (p < 0.001, d = 2.19), respectively, compared with the first set. HR was above 80% HRmax for 4.1 ± 1.2 min during set 1 and this was increased to 5.1 ± 0.4 min in set 2 (p < 0.001, d = 1.15). Likewise, HR was above 90% of HRmax for 2.0 ± 1.2 min in set 1 and was increased to 3.4 ± 1.7 min in set 2 (p < 0.001, d = 0.98). In summary, two 5-min 15 s sets of high-intensity circuit training using sport-specific exercises, increased HR to levels above 80% and 90% HRmax for extended time periods, and thus may be considered as an appropriate stimulus, in terms of intensity, for improving aerobic fitness in child female gymnasts.

Active Video Game Exercise Training Improves the Clinical Control of Asthma in Children: Randomized Controlled Trial

OBJECTIVE

The aim of the present study was to determine whether aerobic exercise involving an active video game system improved asthma control, airway inflammation and exercise capacity in children with moderate to severe asthma.

DESIGN

A randomized, controlled, single-blinded clinical trial was carried out. Thirty-six children with moderate to severe asthma were randomly allocated to either a video game group (VGG; N = 20) or a treadmill group (TG; n = 16). Both groups completed an eight-week supervised program with two weekly 40-minute sessions. Pre-training and post-training evaluations involved the Asthma Control Questionnaire, exhaled nitric oxide levels (FeNO), maximum exercise testing (Bruce protocol) and lung function.

RESULTS

No differences between the VGG and TG were found at the baseline. Improvements occurred in both groups with regard to asthma control and exercise capacity. Moreover, a significant reduction in FeNO was found in the VGG (p < 0.05). Although the mean energy expenditure at rest and during exercise training was similar for both groups, the maximum energy expenditure was higher in the VGG.

CONCLUSION

The present findings strongly suggest that aerobic training promoted by an active video game had a positive impact on children with asthma in terms of clinical control, improvement in their exercise capacity and a reduction in pulmonary inflammation.

TRIAL REGISTRATION

Clinicaltrials.gov NCT01438294.

Fast-start strategy increases the time spent above 95 %VO2max during severe-intensity intermittent running exercise

This study aimed to use the intermittent critical velocity (ICV) model to individualize intermittent exercise and analyze whether a fast-start strategy could increase the time spent at or above 95 %VO(2max) (t95VO(2max)) during intermittent exercise. After an incremental test, seven active male subjects performed three intermittent exercise tests until exhaustion at 100, 110, and 120 % of the maximal aerobic velocity to determine ICV. On three occasions, the subjects performed an intermittent exercise test until exhaustion at 105 % (IE105) and 125 % (IE125) of ICV, and at a speed that was initially set at 125 %ICV but which then decreased to 105 %ICV (IE125-105). The intermittent exercise consisted of repeated 30-s runs alternated with 15-s passive rest intervals. There was no difference between the predicted and actual Tlim for IE125 (300 ± 72 s and 284 ± 76 s) and IE105 (1,438 ± 423 s and 1,439 ± 518 s), but for IE125-105 the predicted Tlim underestimated the actual Tlim (888 ± 211 s and 1,051 ± 153 s, respectively). The t95VO(2max) during IE125-105 (289 ± 150 s) was significantly higher than IE125 (113 ± 40 s) and IE105 (106 ± 71 s), but no significant differences were found between IE125 and IE105. It can be concluded that predicting Tlim from the ICV model was affected by the fast-start protocol during intermittent exercise. Furthermore, fast-start protocol was able to increase the time spent at or above 95 %VO2max during intermittent exercise above ICV despite a longer total exercise time at IE105.

Comparison of the 45-Second/15-Second Intermittent Running Field Test and the Continuous Treadmill Test

Purposes:

To compare the physiological responses and maximal aerobic running velocity (MAV) during an incremental intermittent (45-s run/15-s rest) field test (45-15FIT) vs an incremental continuous treadmill test (TR) and to demonstrate that the MAV obtained during 45-15FIT (MAV45-15) was relevant to elicit a high percentage of maximal oxygen uptake (VO2max) during a 30-s/30-s intermittent training session.

Methods:

Oxygen uptake (VO2), heart rate (HR), and lactate concentration ([La]) were measured in 20 subjects during 2 maximal incremental tests and four 15-min intermittent tests. The time spent above 90% and 95% VO2max (t90% and t95% VO2max, respectively) was determined.

Results:

Maximal physiological parameters were similar during the 45-15FIT and TR tests (VO2max 58.6 ± 5.9 mL · kg−1 · min−1 for TR vs 58.5 ± 7.0 mL · kg−1 · min−1 for 45-15FIT; HRmax 200 ± 8 beats/min for TR vs 201 ± 7 beats/min for 45-15FIT). MAV45-15 was significantly (P < .001) greater than MAVTR (17.7 ± 1.1 vs 15.6 ± 1.4 km/h). t90% and t95% VO2max during the 30-s/30-s performed at MAVTR were significantly (P < .01) lower than during the 30-s/30-s performed at MAV45-15. Similar VO2 during intermittent tests performed at MAV45-15 and at MAVTR can be obtained by reducing the recovery time or using active recovery.

Conclusions:

The results suggested that the 45-15FIT is an accurate field test to determine VO2max and that MAV45-15 can be used during high-intensity intermittent training such as 30-s runs interspersed with 30-s rests (30-s/30-s) to elicit a high percentage of VO2max.

Similarity in physiological and perceived exertion responses to exercise at continuous and intermittent critical power

The purpose of this study was to compare the physiological responses [oxygen uptake (VO(2)), heart rate (HR) and blood lactate concentrations ([BLa])] and the rating of perceived exertion (RPE) response until exhaustion (TTE) at the continuous (CP(c)) and intermittent (CP(i)) critical power workloads. Ten moderately active men (25.5 ± 4.2 years, 74.1 ± 8.0 kg, 177.6 ± 4.9 cm) participated in this study. The incremental test was applied to determine the highest values of oxygen uptake (VO(2max)), heart rate (HR(max)), blood lactate concentrations ([BLa(max)]), and maximal aerobic power (MAP). Continuous and intermittent exhaustive predictive trials were performed randomly. The hyperbolic relation between power and time was used to estimate CP(c) and CP(i). CP(i) was derived from predictive trial results at an effort and recovery ratio of 30:30 s. Exercise at CP(c) and CP(i) as well as the physiological and RPE responses were measured until exhaustion. The values of physiological variables during CP(c) and CP(i) did not differ in either TTE test and were lower than the VO(2max), HR(max) and [BLa(max)] values. RPE was maximal at the end of exercise at CP(c) and CP(i). There was a high correlation between VO(2max) (L min(-1)) and CP(c) and CP(i) intensities (r ≥ 0.90) and between MAP, CP(c) and CP(i) (r ≥ 0.95). Similar physiological and RPE responses were found at CP(c) and CP(i) for the times analyzed.

Comparison of mechanical ventilatory constraints between continuous and intermittent exercises in healthy prepubescent children

BACKGROUND

The aim of this study was to evaluate the occurrence and severity of mechanical ventilatory constraints in healthy prepubescent children during continuous and intermittent exercise.

METHODS

Twelve prepubescent children (7-11 years old) performed 7 exercises on a treadmill: one graded test for the determination of maximal aerobic speed (MAS), three continuous exercises (CE) at 60, 70, and 80% of MAS and three intermittent exercises (IE), alternating 15 sec of exercise with 15 sec of passive recovery, at 90, 100, and 110% of MAS. During each CE and IE, tidal flow/volume loops were plotted within a maximal flow/volume loop (MFVL) measured at rest before each exercise. Expiratory flow limitation (expFL expressed in %Vt) was defined as the part of exercise tidal volume (Vt) meeting the boundary of MFVL. Breathing strategy was estimated by measuring inspiratory capacity relative to forced vital capacity and tidal volume relative to inspiratory capacity. Other breathing pattern parameters (ventilation VE, Vt, respiratory frequency f) were continuously recorded during exercise.

RESULTS

An "intensity" effect was found for VE during CE (P < 0.001) but not during IE (P = 0.08). The increase in VE was predominantly assumed by an increase in f for both exercise modalities. During each exercise, several children heterogeneously experienced expFL ranging between 10 and 90%Vt. For all exercises, Vt was predominantly regulated by an increase in Vt/IC with no change in IC/FVC from rest to exercise. Finally, no significant "modality" effect was found for mechanical ventilatory constraint parameters (expFL, Vt/IC, and IC/FVC).

DISCUSSION

We could conclude that neither of the modalities studied induced more mechanical ventilatory constraints than the other, but that exercise intensities specific to each modality might be greater sources of exacerbation for mechanical ventilatory constraints.

Physiological and perceived exertion responses at intermittent critical power and intermittent maximal lactate steady state

The aim of this study was to compare the power outputs of the intermittent critical power (CPi) with the intermittent maximal lactate steady state (MLSSi) and to compare the physiological and perceptual responses exercising at CPi and MLSSi. Ten subjects performed intermittent trials on a cycle ergometer to determine CPi and MLSSi using 30:30 seconds of effort and pause. The oxygen uptake (&OV0312;o2), heart rate (HR), blood lactate concentration ([Lac]), and rating of perceived exertion (RPE) responses were compared during 30-minute cycling at CPi and MLSSi. The CPi (267 ± 45 W) was similar to MLSSi (254 ± 39 W), and they were correlated (r = 0.88; p < 0.05). The &OV0312;o2 and HR responses stabilized throughout exercising at CPi (2.52 ± 0.52 L·min; 156 ± 8 b·min) and MLSSi (2.41 ± 0.32 L·min; 152 ± 10 b·min). These physiological variables were similar between conditions. However, the [Lac] and RPE were higher from the middle to the end of exercise duration at CPi ([Lac] = 6.9 ± 2.6 mM; RPE = 17.1 ± 2.1 a.u.) compared to MLSSi ([Lac] = 5.1 ± 0.9 mM; RPE = 15.7 ± 1.8 a.u.). Therefore, CPi intensity determined from 30:30 seconds of effort and rest periods on a cycle ergometer is equivalent to the MLSSi, and there is a physiological steady state throughout both exercise intensities, although the [Lac] and RPE responses at CPi are higher than at MLSSi. Thus, the CPi and MLSSi may be used as tools for intermittent training evaluation and prescription.

The extent of aerobic system activation during continuous and interval exercise protocols in young adolescents and men

This study assessed the extent of aerobic system activation in young adolescents and men during heavy continuous (HC), short-interval (SI), and long-interval (LI) aerobic exercise protocols, and compared this response between the 2 age groups in the 3 protocols. Ten young adolescents (aged 13.2 ± 0.3 years) and 10 men (aged 21.0 ± 1.6 years) completed a maximal incremental test, an HC exercise protocol (83% of maximal aerobic velocity; MAV), an SI exercise protocol (30 s at 110% MAV with 30 s at 50%), and an LI exercise protocol (3 min at 95% MAV with 3 min at 35%). Oxygen consumption and heart rate were measured continuously, and blood samples were obtained for lactate determination. Men completed more runs and distance in the SI protocol (p < 0.05) than adolescents; however, there were no age differences in the number of LI runs and in the duration of HC protocol. In both age groups, more time was spent above 90% and 95% of maximal oxygen consumption (p < 0.05), and a higher percentage of maximal oxygen consumption was reached in the LI compared with the HC and SI protocols, with no differences between the HC and SI protocols. Although within each protocol the percentage of maximal oxygen consumption achieved and time spent above 90% and 95% of maximal oxygen consumption was not different between age groups, the time spent at 80% maximal oxygen consumption was longer for adolescents than men in the HC protocol, and longer for men than boys in the SI protocol (p < 0.05). In conclusion, all protocols elicited high levels of aerobic activation in both age groups. The LI protocol taxed the aerobic system at 90%–100% of maximal oxygen consumption for a longer time when compared with the HC and SI protocols in young adolescents and in men. However, differences were observed between groups in taxing the aerobic system at 80% maximal oxygen consumption: in young adolescents, the HC protocol allowed longer running time than the LI and SI protocols, while in men there were no differences among protocols.

The effects of heavy continuous versus long and short intermittent aerobic exercise protocols on oxygen consumption, heart rate, and lactate responses in adolescents

This study compared the physiological responses to heavy continuous (HC), short-intermittent (SI), and long-intermittent (LI) treadmill exercise protocols in non-endurance adolescent males. Nine adolescents (14 +/- 0.6 years) performed a maximal incremental treadmill test followed, on separate days, by a SI [30 s at 110% of maximal aerobic velocity (MAV) with 30 s recovery at 50%], a LI (3 min at 95% of MAV with 3 min recovery at 35%), and a HC (at 83% of MAV) aerobic exercise protocol. VO(2) and HR were measured continuously, and blood samples were obtained prior to and after the protocols. The duration of exercise and the distance covered were longer (p < 0.05) in HC and LI versus SI. All participants reached 80 and 85% of VO(2)peak irrespective of the protocol, while more participants reached 90 and 95% of VO(2)peak in the intermittent protocols (9 and 6, respectively) versus HC (5 and 3, respectively). The time spent above 80 and 85% of VO(2)peak was higher in HC and LI versus SI; the time above 90% was higher only in LI versus SI, and the time above 95% was higher in LI versus HC and SI. The total VO(2) consumed was greater in HC and LI versus SI. Lactate was higher after LI versus HC. In conclusion, when matched for exhaustion level, LI is more effective in stimulating the aerobic system compared to both HC and SI, while HC aerobic exercise appears equally effective to SI. Nevertheless, adolescents have to exercise for a longer time in HC and LI to achieve these effects.