Daryl Parker

The Science of Cycling Physiology and Training - Part 1

AbstractThe aim of this review is to provide greater insight and understanding regarding the scientific nature of cycling. Research findings are presented in a practical manner for their direct application to cycling. The two parts of this review provide information that is useful to athletes, coaches and exercise scientists in the prescription of training regimens, adoption of exercise protocols and creation of research designs.Here for the first time, we present rationale to dispute prevailing myths linked to erroneous concepts and terminology surrounding the sport of cycling. In some studies, a review of the cycling literature revealed incomplete characterisation of athletic performance, lack of appropriate controls and small subject numbers, thereby complicating the understanding of the cycling research. Moreover, a mixture of cycling testing equipment coupled with a multitude of exercise protocols stresses the reliability and validity of the findings.Our scrutiny of the literature revealed key cycling performance-determining variables and their training-induced metabolic responses. The review of training strategies provides guidelines that will assist in the design of aerobic and anaerobic training protocols. Paradoxically, while maximal oxygen uptake (VO2max) is generally not considered a valid indicator of cycling performance when it is coupled with other markers of exercise performance (e.g. blood lactate, power output, metabolic thresholds and efficiency/economy), it is found to gain predictive credibility.The positive facets of lactate metabolism dispel the ‘lactic acid myth’. Lactate is shown to lower hydrogen ion concentrations rather than raise them, thereby retarding acidosis. Every aspect of lactate production is shown to be advantageous to cycling performance. To minimise the effects of muscle fatigue, the efficacy of employing a combination of different high cycling cadences is evident. The subconscious fatigue avoidance mechanism ‘teleoanticipation’ system serves to set the tolerable upper limits of competitive effort in order to assure the athlete completion of the physical challenge.Physiological markers found to be predictive of cycling performance include: (i) power output at the lactate threshold (LT2); (ii) peak power output (Wpeak) indicating a power/weight ratio of ≥5.5 W/kg; (iii) the percentage of type I fibres in the vastus lateralis; (iv) maximal lactate steady-state, representing the highest exercise intensity at which blood lactate concentration remains stable; (v) Wpeak at LT2; and (vi) Wpeak during a maximal cycling test. Furthermore, the unique breathing pattern, characterised by a lack of tachypnoeic shift, found in professional cyclists may enhance the efficiency and metabolic cost of breathing. The training impulse is useful to characterise exercise intensity and load during training and competition. It serves to enable the cyclist or coach to evaluate the effects of training strategies and may well serve to predict the cyclist’s performance.Findings indicate that peripheral adaptations in working muscles play a more important role for enhanced submaximal cycling capacity than central adaptations. Clearly, relatively brief but intense sprint training can enhance both glycolytic and oxidative enzyme activity, maximum short-term power output and VO2max. To that end, it is suggested to replace ~15% of normal training with one of the interval exercise protocols. Tapering, through reduction in duration of training sessions or the frequency of sessions per week while maintaining intensity, is extremely effective for improvement of cycling time-trial performance. Overuse and over-training disabilities common to the competitive cyclist, if untreated, can lead to delayed recovery.

The Science of Cycling Factors Affecting Performance - Part 2

AbstractThis review presents information that is useful to athletes, coaches and exercise scientists in the adoption of exercise protocols, prescription of training regimens and creation of research designs. Part 2 focuses on the factors that affect cycling performance. Among those factors, aerodynamic resistance is the major resistance force the racing cyclist must overcome. This challenge can be dealt with through equipment technological modifications and body position configuration adjustments. To successfully achieve efficient transfer of power from the body to the drive train of the bicycle the major concern is bicycle configuration and cycling body position. Peak power output appears to be highly correlated with cycling success. Likewise, gear ratio and pedalling cadence directly influence cycling economy/efficiency. Knowledge of muscle recruitment throughout the crank cycle has important implications for training and body position adjustments while climbing. A review of pacing models suggests that while there appears to be some evidence in favour of one technique over another, there remains the need for further field research to validate the findings. Nevertheless, performance modelling has important implications for the establishment of performance standards and consequent recommendations for training.

Physiological and anthropometric determinants of sport climbing performance

Objective—To identify the physiological and anthropometric determinants of sport climbing performance. Methods—Forty four climbers (24 men, 20 women) of various skill levels (self reported rating 5.6–5.13c on the Yosemite decimal scale) and years of experience (0.10–44 years) served as subjects. They climbed two routes on separate days to assess climbing performance. The routes (11 and 30 m in distance) were set on two artificial climbing walls and were designed to become progressively more difficult from start to finish. Performance was scored according to the system used in sport climbing competitions where each successive handhold increases by one in point value. Results from each route were combined for a total climbing performance score. Measured variables for each subject included anthropometric (height, weight, leg length, arm span, % body fat), demographic (self reported climbing rating, years of climbing experience, weekly hours of training), and physiological (knee and shoulder extension, knee flexion, grip, and finger pincer strength, bent arm hang, grip endurance, hip and shoulder flexibility, and upper and lower body anaerobic power). These variables were combined into components using a principal components analysis procedure. These components were then used in a simultaneous multiple regression procedure to determine which components best explain the variance in sport rock climbing performance. Results—The principal components analysis procedure extracted three components. These were labelled training, anthropometric, and flexibility on the basis of the measured variables that were the most influential in forming each component. The results of the multiple regression procedure indicated that the training component uniquely explained 58.9% of the total variance in climbing performance. The anthropometric and flexibility components explained 0.3% and 1.8% of the total variance in climbing performance respectively. Conclusions—The variance in climbing performance can be explained by a component consisting of trainable variables. More importantly, the findings do not support the belief that a climber must necessarily possess specific anthropometric characteristics to excel in sport rock climbing.

Breathing patterns and cardiovascular autonomic modulation during hypoxia induced by simulated altitude.

Objective To assess the influence of different breathing patterns on autonomic cardiovascular modulation during acute exposure to altitude-induced hypoxia. Design We measured relative changes in minute ventilation (VE), oxygen saturation (%SaO2), spectral analysis of RR interval and blood pressure, and response to stimulation of carotid baroreceptors (neck suction) at baseline and after acute (1 h) hypobaric hypoxia (equivalent to 5000 m, in a hypobaric chamber). Methods We studied 19 human subjects: nine controls and 10 Western yoga trainees of similar age, while breathing spontaneously, at 15 breaths/min (controlled breathing) and during ‘complete yogic breathing’ (slow diaphragmatic + thoracic breathing, ∼ 5 breaths/min) in yoga trainees, or simple slow breathing in controls. Results At baseline %SaO2, VE and autonomic pattern were similar in both groups; simulated altitude increased VE in controls but not in yoga trainees; %SaO2 decreased in all subjects (P < 0.0001), but more in controls than in yoga trainees (17 versus 12%, 14 versus 9%, 14 versus 8%, all P < 0.05 or better, during spontaneous breathing, controlled breathing and yogic or slow breathing, respectively). Simulated altitude decreased RR interval (from 879 ± 45 to 770 ± 39, P < 0.01) and increased indices deducted from spectral analysis of heart rate variability (low frequency/high frequency (LF/HF) ratio from 1.6 ± 0.5 to 3.2 ± 1.1, P < 0.05) and systolic blood pressure (low-frequency fluctuations from 2.30 ± 0.31 to 3.07 ± 0.24 ln-mmHg2, P < 0.05) in controls, indicating sympathetic activation; these changes were blunted in yoga trainees, and in both groups during slow or yogic breathing. No effect of altitude was seen on stimulation of carotid baroreceptors in both groups. Conclusions Well-performed slow yogic breathing maintains better blood oxygenation without increasing VE (i.e. seems to be a more efficient breathing) and reduces sympathetic activation during altitude-induced hypoxia.

Multiple variables explain the variability in the decrement in V??O2max during acute hypobaric hypoxia

PURPOSE We used multiple regression analyses to determine the relationships between the decrement in sea level (SL, 760 Torr) VO2max during hypobaric hypoxia (HH) and variables that could alter or be related to the decrement in VO2max. METHODS HH conditions consisted of 682 Torr, 632 Torr, and 566 Torr, and the measured independent variables were SL-VO2max, SL lactate threshold (SL-LT), the change in hemoglobin saturation at VO2max between 760 and 566 Torr (delta SaO2max), lean body mass (LBM), and gender. Male (N = 14) and female (N = 14) subjects of varied fitness, training status, and residential altitude (1,640-2,460 m) completed cycle ergometry tests of VO2max at each HH condition under randomized and single-blinded conditions. RESULTS VO2max decreased significantly from 760 Torr after 682 Torr (approximately 915 m) (3.5 +/- 0.9 to 3.4 +/- 0.8 L.min-1, P = 0.0003). Across all HH conditions, the slope of the relative decrement in VO2max (%VO2max) during HH was -9.2%/100 mm Hg (-8.1%/1000 m) with an initial decrease from 100% estimated to occur below 705 Torr (610 m). Step-wise multiple regression revealed that SL-VO2max, SL-LT, delta SaO2max, LBM, and gender each significantly combined to account for 89.03% of the variance in the decrement in VO2max (760-566 Torr) (P < 0.001). CONCLUSIONS Individuals who have a combination of a large SL-VO2max, a small SL-LT (VO2, L.min-1), greater reductions in delta SaO2max, a large LBM, and are male have the greatest decrement in VO2max during HH. The unique variance explanation afforded by SL-LT, LBM, and gender suggests that issues pertaining to oxygen diffusion within skeletal muscle may add to the explanation of between subjects variability in the decrement in VO2max during HH.

Variables contributing to acute mountain sickness on the summit of Mt Whitney.

Abstract Objective.—The interaction of 15 variables representing physical characteristics, previous altitude exposure, and ascent data was analyzed to determine their contribution to acute mountain sickness (AMS). Methods.—Questionnaires were obtained from 359 volunteers upon reaching the summit of Mt Whitney (4419 m). Heart rate and arterial oxygen saturation were measured with a pulse oximeter, and AMS was identified by Lake Louise Self-Assessment scoring. Multiple logistic regression analysis was used to identify significant protective and risk factors for AMS. Results.—Thirty-three percent of the sample met the criteria for AMS. The odds of experiencing AMS were greater for those who reported a previous altitude illness (adjusted odds ratio [OR] = 2.00, P < .01) or who were taking analgesics during the ascent (adjusted OR = 2.09, P < .01). Odds for AMS decreased with increasing age (adjusted OR = 0.82, P < .0001), a greater number of climbs above 3000 m in the past month (adjusted OR = 0.92, P < .05), and use of acetazolamide during the ascent (adjusted OR = 0.33, P < .05). Conclusions.—The significant determinants of AMS on the summit of Mt Whitney were age, a history of altitude illness, number of climbs above 3000 m in the past month, and use of acetazolamide and analgesics during ascent.

Mt. Whitney: Determinants of Summit Success and Acute Mountain Sickness

PURPOSE The aim of this study was to determine the prevalence of summit success and acute mountain sickness (AMS) on Mt. Whitney (4419 m) and to identify variables that contribute to both. METHODS Hikers (N = 886) attempting the summit were interviewed at the trailhead upon their descent. Questionnaires included demographic and descriptive data, acclimatization and altitude history, and information specific to the ascent. The Lake Louise Self-Assessment Score was used to make a determination about the occurrence of AMS. Logistic regression techniques were used to calculate odds ratios (OR) for AMS and summit success. RESULTS Forty-three percent of the sample met the criteria for AMS, and 81% reached the summit. The odds of experiencing AMS were reduced with increases in age (adjusted 10-yr OR = 0.78; P < 0.001), number of hours spent above 3000 m in the 2 wk preceding the ascent (adjusted 24-h OR = 0.71; P < 0.001), and for females (OR = 0.68; P = 0.02). Climbers who had a history of AMS (OR = 1.41; P = 0.02) and those taking analgesics (OR = 2.39; P < 0.001) were more likely to experience AMS. As climber age increased, the odds of reaching the summit decreased (adjusted 10-yr OR = 0.75; P < 0.001). However, increases in the number of hours per week spent training (adjusted 5-h OR = 1.24; P = 0.05), rate of ascent (adjusted 50 m x h(-1) OR = 1.13; P = 0.04), and previous high-altitude record (adjusted 500 m OR = 1.26; P < 0.001) were all associated with increased odds for summit success. CONCLUSIONS A high percentage of trekkers reached the summit despite having symptoms of AMS.

Persistence of baroreceptor control of cerebral blood flow velocity at a simulated altitude of 5000 m.

Objective To assess the effects of acute exposure to simulated high altitude on baroreflex control of mean cerebral blood flow velocity (MCFV). Patients and methods We compared beat-to-beat changes in RR interval, arterial blood pressure, mean MCFV (by transcranial Doppler velocimetry in the middle cerebral artery), end-tidal CO2, oxygen saturation and respiration in 19 healthy subjects at baseline (Albuquerque, 1779 m), after acute exposure to simulated high altitude in a hypobaric chamber (barometric pressure as at 5000 m) and during oxygen administration (to achieve 100% oxygen saturation) at the same barometric pressure (HOX). Baroreflex control on each signal was assessed by univariate and bivariate power spectral analysis performed on time series obtained during controlled (15 breaths/min) breathing, before and during baroreflex modulation induced by 0.1-Hz sinusoidal neck suction. Results At baseline, neck suction was able to induce a clear increase in low-frequency power in MCFV (P < 0.001) as well as in RR and blood pressure. At high altitude, MCFV, as well as RR and blood pressure, was still able to respond to neck suction (all P < 0.001), compared to controlled breathing alone, despite marked decreases in end-tidal CO2 and oxygen saturation at high altitude. A similar response was obtained at HOX. Phase delay analysis excluded a passive transmission of low-frequency oscillations from arterial pressure to cerebral circulation. Conclusions During acute exposure to high altitude, cerebral blood flow is still modulated by the autonomic nervous system through the baroreflex, whose sensitivity is not affected by changes in CO2 and oxygen saturation levels.

Mitochondrial efficiency and exercise economy following heat stress: a potential role of uncoupling protein 3

Heat stress has been reported to reduce uncoupling proteins (UCP) expression, which in turn should improve mitochondrial efficiency. Such an improvement in efficiency may translate to the systemic level as greater exercise economy. However, neither the heat‐induced improvement in mitochondrial efficiency (due to decrease in UCP), nor its potential to improve economy has been studied. Determine: (i) if heat stress in vitro lowers UCP3 thereby improving mitochondrial efficiency in C2C12 myocytes; (ii) whether heat acclimation (HA) in vivo improves exercise economy in trained individuals; and (iii) the potential improved economy during exercise at altitude. In vitro, myocytes were heat stressed for 24 h (40°C), followed by measurements of UCP3, mitochondrial uncoupling, and efficiency. In vivo, eight trained males completed: (i) pre‐HA testing; (ii) 10 days of HA (40°C, 20% RH); and (iii) post‐HA testing. Pre‐ and posttesting consisted of maximal exercise test and submaximal exercise at two intensities to assess exercise economy at 1600 m (Albuquerque, NM) and 4350 m. Heat‐stressed myocytes displayed significantly reduced UCP3 mRNA expression and, mitochondrial uncoupling (77.1 ± 1.2%, P < 0.0001) and improved mitochondrial efficiency (62.9 ± 4.1%, P < 0.0001) compared to control. In humans, at both 1600 m and 4350 m, following HA, submaximal exercise economy did not change at low and moderate exercise intensities. Our findings indicate that while heat‐induced reduction in UCP3 improves mitochondrial efficiency in vitro, this is not translated to in vivo improvement of exercise economy at 1600 m or 4350 m.

PREFERRED AND ENERGETICALLY OPTIMAL TRANSITION SPEEDS IN BACKWARD HUMAN LOCOMOTION

Some aspects of backward locomotion are similar to forward locomotion, while other aspects are not related to their forward counterpart. The backward preferred transition speed (BPTS) has never been directly compared to the energetically optimal transition speed (EOTS), nor has it been compared to the preferred transition speed (PTS) during forward locomotion. The purpose of this study was to determine whether the BPTS occurs at the EOTS, and to examine the relationship between the backward and forward preferred gait transition speeds. The preferred backward and forward transition speeds of 12 healthy, young subjects (7 males, 5 females) were determined after subjects were familiarized with forward and backward treadmill locomotion. On a subsequent day, subjects walked backward at speeds of 70, 80, 90, 100, and 110% of the BPTS and ran backward at speeds of 60, 75, 90, 100, and 120% of the BPTS while VO2 and RPE data were collected. After subtracting standing VO2, exercise VO2 was normalized to body mass and speed. For each subject, energy-speed curves for walking and running were fit to the normalized data points. The intersection of these curves was defined as the EOTS which was compared to the BPTS using a paired t-test (p < 0.05). RPE and VO2 at the BPTS were also compared between walking and running conditions, and the correlation between BPTS and PTS was calculated. The EOTS (1.85 ± 0.09 m·s(-1)) was significantly greater than the BPTS (1.63 ± 0.11 m·s(-1)). Even though RPE was equal for walking and running at the BPTS, VO2 was significantly greater when running. There was a strong correlation (r = 0.82) between the BPTS and the PTS. Similar to forward locomotion, the determinants of the BPTS must include factors other than metabolic energy. The gait transition during backward locomotion exhibits several similarities to its forward counterpart. Key PointsThe backward preferred transition speed (1.63 ± 0.11 m·s(-1)) was significantly less than the energetically optimal transition speed (1.85 ± 0.09 m·s(-1)), similar to what is observed during forward locomotion.RPE was equal for walking and running at the backward preferred transition speed.There was a strong correlation (r = 0.82) between the backward and forward preferred transition speeds.Similar to forward locomotion, the determinants of the BPTS must include factors other than metabolic energy.