Variable versus constant power strategies during cycling time-trials: Prediction of time savings using an up-to-date mathematical model

Abstract

Swain (1997 Swain, D. P. 1997. A model for optimizing cycling performance by varying power on hills and in wind. Medicine and Science in Sports and Exercise, 29: 1104–1108. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]) employed the mathematical model of Di Prampero et al. (1979 Di Prampero, P. E., Cortili, G., Mognoni, P. and Saibene, F. 1979. Equation of motion of a cyclist. Journal of Applied Physiology, 47: 201–206. [PubMed], [Web of Science ®] , [Google Scholar]) to predict that, for cycling time-trials, the optimal pacing strategy is to vary power in parallel with the changes experienced in gradient and wind speed. We used a more up-to-date mathematical model with validated coefficients (Martin et al., 1998 Martin, J. C., Milliken, D. L., Cobb, J. E., McFadden, K. L. and Coggan, A. R. 1998. Validation of a mathematical model for road cycling power. Journal of Applied Biomechanics, 14: 276–291. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]) to quantify the time savings that would result from such optimization of pacing strategy. A hypothetical cyclist (mass = 70 kg) and bicycle (mass = 10 kg) were studied under varying hypothetical wind velocities (?10 to 10 m · s^?1), gradients (?10 to 10%), and pacing strategies. Mean rider power outputs of 164, 289, and 394 W were chosen to mirror baseline performances studied previously. The three race scenarios were: (i) a 10-km time-trial with alternating 1-km sections of 10% and ?10% gradient; (ii) a 40-km time-trial with alternating 5-km sections of 4.4 and ?4.4 m · s^?1 wind (Swain, 1997 Swain, D. P. 1997. A model for optimizing cycling performance by varying power on hills and in wind. Medicine and Science in Sports and Exercise, 29: 1104–1108. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]); and (iii) the 40-km time-trial delimited by Jeukendrup and Martin (2001 Jeukendrup, A. E. and Martin, J. 2001. Improving cycling performance: How should we spend our time and money?. Sports Medicine, 31: 559–569. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]). Varying a mean power of 289 W by ± 10% during Swain's (1997 Swain, D. P. 1997. A model for optimizing cycling performance by varying power on hills and in wind. Medicine and Science in Sports and Exercise, 29: 1104–1108. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]) hilly and windy courses resulted in time savings of 126 and 51 s, respectively. Time savings for most race scenarios were greater than those suggested by Swain (1997 Swain, D. P. 1997. A model for optimizing cycling performance by varying power on hills and in wind. Medicine and Science in Sports and Exercise, 29: 1104–1108. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]). For a mean power of 289 W over the “standard” 40-km time-trial, a time saving of 26 s was observed with a power variability of 10%. The largest time savings were found for the hypothetical riders with the lowest mean power output who could vary power to the greatest extent. Our findings confirm that time savings are possible in cycling time-trials if the rider varies power in parallel with hill gradient and wind direction. With a more recent mathematical model, we found slightly greater time savings than those reported by Swain (1997 Swain, D. P. 1997. A model for optimizing cycling performance by varying power on hills and in wind. Medicine and Science in Sports and Exercise, 29: 1104–1108. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]). These time savings compared favourably with the predicted benefits of interventions such as altitude training or ingestion of carbohydrate-electrolyte drinks. Nevertheless, the extent to which such power output variations can be tolerated by a cyclist during a time-trial is still unclear.     

Effects of magnitude and frequency of variations in external power output on simulated cycling time-trial performance

Abstract

Mechanical models of cycling time-trial performance have indicated adverse effects of variations in external power output on overall performance times. Nevertheless, the precise influences of the magnitude and number of these variations over different distances of time trial are unclear. A hypothetical cyclist (body mass 70 kg, bicycle mass 10 kg) was studied using a mathematical model of cycling, which included the effects of acceleration. Performance times were modelled over distances of 4–40 km, mean power outputs of 200–600 W, power variation amplitudes of 5–15% and variation frequencies of 2–32 per time-trial. Effects of a “fast-start” strategy were compared with those of a constant-power strategy. Varying power improved 4-km performance at all power outputs, with the greatest improvement being 0.90 s for ± 15% power variation. For distances of 16.1, 20 and 40 km, varying power by ± 15% increased times by 3.29, 4.46 and 10.43 s respectively, suggesting that in long-duration cycling in constant environmental conditions, cyclists should strive to reduce power variation to maximise performance. The novel finding of the present study is that these effects are augmented with increasing event distance, amplitude and period of variation. These two latter factors reflect a poor adherence to a constant speed.     

场地自行车4 000 m追逐赛不同起动方式摄氧动力模型的分析

目的：研究4 000 m场地自行车运动VO2反应,及前15 s高功率起动对运动成绩的影响。方法：11名男子自行车运动员在功率车上进行递增负荷试验和两种不同起动强度的4 000 m运动。首先进行前60 s平均功率（128±2）%MAP即（501.7±41.9）w强度对照模式运动;5 h后进行模拟模式运动,强度在第8~10 s达到最高值235%MAP（928.3±77.6）w,后逐步下降,15 s时至平均功率（421.9±40.1）w,维持15~60 s。60 s之后两组均进行自由速度模式,强度控制在380~420 w之间。结果：整个测试过程模拟组较对照组平均功率高19 w左右,有统计学差异。模拟组15~60 sVO2高于对照组,模拟组15s~60sVO2高于对照组,而AOD却低于对照组,对整个运动表现有促进作用。结论：4 000 m场地自行车运动前15 s高输出功率可伴随着更快的VO2反应而不是单一归于节省时间理论,并可促进中等距离自行车计时运动员的摄氧动员能力。     

Effects of radiant heat exposure on pacing pattern during a 15-km cycling time trial

Abstract

The goal of this study was to investigate the effects of different durations of skin temperature manipulation on pacing patterns and performance during a 15-km cycling time trial. Nineteen well-trained men completed three 15-km cycling time trials in 18°C and 50% relative humidity with 4.5-km (short-heat), 9.0-km (long-heat) or without (control) radiant heat exposure applied by infrared heaters after 1.5 km in the time trial. During the time trials, power output, mean skin temperature, rectal temperature, heart rate and rating of perceived exertion were assessed. The radiant heat exposure resulted in higher mean skin temperature during the time trial for short-heat (35.0 ± 0.6°C) and long-heat (35.3 ± 0.5°C) than for control (32.5 ± 1.0°C; P < 0.001), whereas rectal temperature was similar (P = 0.55). The mean power output was less for short-heat (273 ± 8 W; P = 0.001) and long-heat (271 ± 9 W; P = 0.02) than for control (287 ± 7 W), but pacing patterns did not differ (P = 0.55). Heart rate was greatest in control (177 ± 9 beats · min^?1; P < 0.001), whereas the rating of perceived exertion remained similar. We concluded that a radiant heat exposure and associated higher skin temperature reduced overall performance, but did not modify pacing pattern during a 15-km cycling time trial, regardless of the duration of the exposure.     

Effect of environmental feedbacks on pacing strategy and affective load during a self-paced 30 min cycling time trial

The purpose of this study was to analyze the pacing strategy and its affective consequences during self-paced cycling time trials (TT) performed at different severity of hypoxia. Eight competitive cyclists performed five 30 min self-paced TTs at their best performance in the following conditions: 1) normobaric normoxia (NN_SL); 2) normobaric hypoxia under two simulated altitudes: 2000 m (NH₂₀₀₀) and 3500 m (NH₃₅₀₀) and 3) normobaric hypoxia but the cyclists were deceived and thought to be at sea level for 2000 m (DecNH₂₀₀₀) and 3500 m (DecNH₃₅₀₀). Power Output (PO), oxygen uptake (VO₂), and blood lactate concentration ([La]) were recorded to assess exercise intensity and physiological adaptations. The rate of perceived exertion (RPE) and pleasure were measured with a CR10 Borg scale to evaluate the affective load (AL). PO and VO₂ decreased with the severity of hypoxia but no significantly difference on performance was measured between deceived and real conditions, except for pacing strategy. The started intensity depends on the exercise expectations, but PO was rapidly adjusted with the physiological constraints and the rate of increase of RPE. Finally, AL did not reach maximal values so that the athletes sustained a physiological and emotional reserve to perform a final spurt.     

Respiratory responses and rating of perceived exertion of severely obese adolescents during continuous and intermittent graded walking protocols: Application to cardiorespiratory field tests

ABSTRACT

During 20 m shuttle tests, obese adolescents may have difficulty achieving maximum cardiorespiratory performance due to the presence of braking-relaunch phases (BRP). Nineteen obese adolescents aged 15.2 ± 1.5 years (body mass index [BMI] = 39.7 ± 5.9 kg.m^?2) performed three graded walking exercises on a 50 m track at speeds between 3 and 6 km/h: a continuous-straight-line protocol (C), a continuous protocol that required turning back every 30 sec (C-BRP) and an intermittent protocol that consisted of successively walking then resting for 15 sec (15–15). Oxygen uptake (VO₂), aerobic cost of walking (Cw), ventilation (VE) and rating of perceived exertion (RPE) were measured at each stage during the protocols. During C-BRP, the responses were not significantly higher compared with C (p > 0.30). During 15–15, the VO₂, Cw and VE were ~ 15 to 25% lower than during C beginning at 4 km/h (p < 0.05). In obese adolescents, the respiratory impact of sudden directional changes during the 20 m shuttle-type test appeared to be minor at walking speeds. During the 15–15 test, the intensity increases more progressively, and this design may encourage obese adolescents to walk further than during a continuous test.     

Relative shank to thigh length is associated with different mechanisms of power production during elite male ergometer rowing

The effect of anthropometric differences in shank to thigh length ratio upon timing and magnitude of joint power production during the drive phase of the rowing stroke was investigated in 14 elite male rowers. Rowers were tested on the RowPerfect ergometer which was instrumented at the handle and foot stretcher to measure force generation, and a nine segment inverse dynamics model used to calculate the rower's joint and overall power production. Rowers were divided into two groups according to relative shank thigh ratio. Time to half lumbar power generation was significantly earlier in shorter shank rowers (p = 0.028) compared to longer shank rowers, who showed no lumbar power generation during the same period of the drive phase. Rowers with a relatively shorter shank demonstrated earlier lumbar power generation during the drive phase resulting from restricted rotation of the pelvic segment requiring increased lumbar extension in these rowers. Earlier lumbar power generation and extension did not appear to directly affect performance measures of the short shank group, and so can be attributed to a technical adaptation developed to maximise rowing performance.     

Unprompted vigorous physical activity is associated with higher levels of subsequent sedentary behaviour in participants with low cardiorespiratory fitness: a cross-sectional study

Abstract

Performing physical activity is considered health promoting but may induce a need for subsequent rest periods. This study aimed to determine the within-day interactions between vigorous physical activity (VPA) and sedentary behaviour (SB) in participants with low cardiorespiratory fitness. We tested the hypothesis that VPA is associated with a temporary subsequent increase in SB. One week of accelerometer data containing a minimum of one 10-min bout of VPA from 62 participants with low cardiorespiratory fitness (31–50 years old) were obtained from the MILE study. A comparison of SB was made between days with a bout of VPA and days without (control). Due to a positive association between VPA and number and duration of sedentary bouts, the time accumulated in both uninterrupted and total sedentary bouts were 27 (95% CI, 10–45)?min and 29 (95% CI, 9–50)?min higher on VPA days compared to control days (P?<?0.05). Our results indicate that in participants with low cardiovascular fitness, unprompted VPA is positively associated with an increase in subsequent sedentary time. We propose that such VPA-associated sedentary time may be viewed as part of a healthy activity pattern.     

Impact of compliance with different guidelines on physical activity during pregnancy and perceived barriers to leisure physical activity

Abstract

The aims of the this prospective study were to analyse physical activity (PA) engagement during the first and second trimesters, considering the different guidelines published on PA, to document the individual characteristics associated with the accomplishment of these guidelines and to examine pregnant women’s perceived barriers to leisure PA, using a socioecological framework. A sample of 133 pregnant women in two stages – at 10–12 weeks’ gestation (T1) and 20–22 weeks’ gestation (T2) – were evaluated. PA was assessed by accelerometry during the T1 and T2 evaluation stages. Socio-demographic characteristics, lifestyle factors and barriers to leisure PA were assessed via questionnaire. A large proportion of women (ranging from 32% to 96%) did not reach the levels of PA recommended by the guidelines. There were no significant differences between T1 and T2 with regard to compliance with PA recommendations. A decrease in PA levels from T1 to T2 was noted for all recommendations. No associations were found between participants’ characteristics and adherence to the recommendations in T1 and T2. No significant differences were found in barriers to leisure PA between T1 and T2. The most commonly reported barriers to leisure PA were intrapersonal, not health related. Our results indicate that there were no differences between trimesters regarding compliance of PA recommendations, and perceived barriers were similar in both trimesters.     

不同负荷强度运动时表面肌电图中位频率与血乳酸浓度变化的关系

采用等速运动方式 ,以表面肌电图和血乳酸为指标 ,在 10 %、3 0 %和 50 %MVC三种负荷条件下 ,对肘关节屈伸运动时的肱三头肌、肱二头肌和前腕骨肌的表面肌电图和血乳酸浓度的变化进行了比较分析。结果表明 :(1)肘关节屈伸运动时 ,伸展运动的力矩峰值下降幅度大于屈曲运动。 (2 )以 3 0 %和 50 %MVC负荷强度运动时 ,出现了表面肌电图的MF值逐步下降和血乳酸浓度逐渐增加的现象 ;工作肌群MF下降幅度 ,由大到小依次为肱三头肌 >肱二头肌 >前腕骨肌。 (3 )肱三头肌、肱二头肌和前腕骨肌的表面肌电图的MF变化与血乳酸浓度变化相互比较 ,10 %、3 0 %和 50 %MVC三种运动形式都表现出了非常明显的相关性。实验结果可以说明 ,sEMG作为特异性良好的非损伤性检测手段 ,不但能够直观地反映肌肉的收缩活动 ,还与肌肉组织代谢变化有一定的相关关系