MINERVA MEDICA COPYRIGHT

Transcription

1 Aim. The aim of this study was to compare the exercise intensity and competition load during Time Trial (TT), Flat (FL), Medium Mountain (MM) and High Mountain (HM) stages based heart rate (HR) and session rating of perceived exertion (RPE). Methods. We monitored both HR and RPE of 12 professional cyclists during two consecutive 21-day cycling races (Vuelta a España) in order to analyze the exercise intensity and competition load (TRIMP HR and TRIMP RPE ). Results. The highest (P<0.05) mean HR was found in TT (169±2 bpm) versus those observed in FL (135±1 bpm), MM (139±3 bpm), HM (143±1 bpm). However, higher (P<0.05) session RPE were found in HM (7.3±0.2) and MM (7.0±0.3) vs. TT (5.5±0.4) and FL (4.6±0.2). TRIMP HR and TRIMP RPE increased significantly (P<0.05) in the following order: TT, FL, MM and HM. The greatest (P<0.05) TRIMP HR km -1 and TRIMP RPE km -1 were obtained in TT (~4 units) and HM (~12 units), respectively. We found significant (p<0.001) correlations between TRIMP HR and TRIMP RPE in TT (r=0.62), FL (r=0.74), MM (r=0.89) and HM (r=0.78). Conclusion. In conclusion, professional cycling is a highly demanding sport which exercise intensity and competition load varied according to the type of stages. The session RPE method is a valid estimate of internal load during different cycling stage categories. Key words: Exercise - Athletic performance - Bicycling. Cyclists performance in multi-stage races (e.g., Tour) is determined by their ability to perform in different situations. Tour races are composed of different types of stages, i.e., flat stages, mountain stages (medium and high) and time trials. Performance, particularly in time trial and high mountain stages provides a large J SPORTS MED PHYS FITNESS 2013;53: Effect of cycling competition type on effort based on heart rate and session rating of perceived exertion Corresponding author: J. A. Rodríguez-Marroyo, Department of Physical Education and Sports, University of León, León, Spain. j.marroyo@unileon.es J. A. 1, J. G. VILLA 1, G. FERNANDEZ 1, C. FOSTER 2 1Department of Physical Education and Sports Institute of Biomedicine (IBIOMED) University of León, León, Spain 2Department of Exercise and Sport Science University of Wisconsin-La Crosse, La Crosse, USA contribution to the overall outcome of the tours, modified by crashes and tactical decisions. The mountain and time trial stages is also where higher exercise intensity and competition load have been observed. 1-5 Mountain stages are defined by the characteristics of the mountain passes (i.e., slope, altitude, distance). 6 Stages with a greater number of mountain passes and/or higher category (i.e., special or hors and first category) are classified as high mountain stages. Stages where the number of mountain passes to ascend and their difficulty is lower (i.e., second and third category) are classified as medium mountain stages. 4 Similarly, the time trial stages can also be classified into different categories according to their length, topography and racing format: prologue, short, long, uphill and team time trial. 3 Knowledge of the demands of different stages that compose the cycling Tour races is critical to the design of both training programs and overall race strategy. Traditionally, heart rate (HR) has been used both to assess the exercise intensity and to calculate the competition load. 1-5 However, factors such as hydration status, glycogen depletion, altitude and temperature can influence the HR response. 7 Moreover, it has been suggested that HR is a poor indicator of the intensity effort during high intensity exercise such as interval training or intermittent training (e.g., break away and chase efforts in 154 THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS April 2013

2 cycling races). 8 Some authors have proposed the use of session rating of perceived exertion (RPE) as an alternative method to assess both exercise intensity and internal training load To the best of our knowledge no study has monitored the session RPE during different types of stages in professional cycling races. The session RPE method can be a useful tool that allows coaches to quantify the internal load in a simple and non-invasive way, which may also account for physiologic strain which is not well reflected by HR. Therefore, the aim of this study was to compare the exercise intensity and internal load a cycling Grand Tour based on both HR and session RPE. Subjects Materials and methods Twelve professional cyclists (mean±sem, age 25±1 yr, height 175±3 cm, body mass 65.9±2.0 kg and maximal VO ±1.7 ml kg -1 min -1 ) belonging to a Continental Team of the International Cycling Union participated in this study. All cyclists were non-contending riders, in that they did not compete for the General Classification but rather sought stage victories or sub-awards (e.g., points, mountains) or rode in support of contending riders (i.e. domestiques). Written informed consent was obtained from the subjects before starting the study, which was approved by the Ethics Committee of the University of León, Spain. Experimental design The study was performed in two parts. In the first part, each cyclist performed an incremental test to determine the workload at which ventilatory (VT) and respiratory compensation thresholds (RCT) occurred. The second part consisted of the individual monitoring of both the HR response and the session RPE during each of the 21 stages of the Vuelta a España, in order to analyze the exercise intensity and competition load based on HR 1-6 and RPE. 8, 9, 13 Laboratory assessment A week before the start of the Vuelta a España, the cyclists performed an incremental test to exhaustion on a cyclosimulator (Cateye CS-1000, Cateye Co., Osaka, Japan). The test started at 32 km h -1 and the speed was increased by 1 km h -1 every 1 min until the cyclist was not able to maintain the set speed. 5, 6 HR (Polar Vantage NV, Polar Electro Oy, Finland) and respiratory gas exchange (Medical Graphics System CPX-Plus, Medical Graphics Corporation, Minnesota, USA) were measured through the test. The ventilatory and respiratory compensation thresholds were identified according to the following criteria: 14 increase in both ventilation equivalent for oxygen (VE VO 2-1) and end-tidal partial pressure of oxygen with no concomitant increase in ventilation equivalent for carbon dioxide (VE VCO 2-1) for VT, and an increase in both VE VO 2-1 and VE VCO 2-1 and a decrease in end-tidal partial pressure of carbon dioxide for RCT. Competition data All stages of two consecutive Vueltas a España (2004 and 2005 editions) were analyzed. The stages were classified according to the criteria previously adopted by other authors 4 into Time Trial (TT), Flat (FL), Medium Mountain (MM) and High Mountain (HM) stages. Each cyclist s HR was recorded every 5-s (Polar S720i TM, Polar Electro Oy, Filand) during every stage. Subsequently, using proprietary software (Polar Precision Performance v4.0, Polar Electro Oy, Finland), the data were downloaded to determine the cumulative time at various effort intensities. Three intensity zones were established according to the laboratory reference HR values corresponding to the VT and RCT: 2, 5, 6 zone 1 (Z1) below VT (low intensity exercise), zone 2 (Z2) between VT and RCT (moderate intensity exercise) and zone 3 (Z3) above RCT (hard intensity exercise). These zones were used to calculate the competition load (TRIMP HR ) by multiplying the time spent daily in Z1, Z2, and Z3 by constant values of 1, 2, and 3, respectively. The total score (i.e. competition load) was obtained by summating the results of the 3 phases. 8 In addition, the RPE was obtained using the category ratio (0-10) RPE scale 14 ~30 min following the end of the stage (e.g. the session RPE). 8, 9, 13 We calculated the competition load as the session RPE (TRIMP RPE ) multiplied by the duration of the stage in minutes. 8, 9, 13 The TRIMP scores were divided by the length of stages for their normalization (TRIMP km -1 ). Vol No. 2 THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS 155

3 Statistical analysis The results are expressed as mean ± standard error of the mean (SEM). The exercise intensity and competition load were analysed using ANOVA with repeated measures. When a significant F value was found, Bonferroni s test was applied to establish significant differences between means. Values for P<0.05 were considered statistically significant. The relationship between variables was determined by using Pearson correlation coefficient (r). SPSS+ V.15.0 statistical software (Chicago, IL, USA) was used. Table I. Total kilometers per week (percentage of total kilometers) according to the type of stage. Results Table I shows the kilometers distribution per week of the different stages analyzed in the Vuelta a España. Stages kilometers decreased significantly Edition 2004 Edition 2005 Mean±SEM 1 st week TT 27.7 (0.9) 7.0 (0.2) 17.4±10.4 (0.6±0.3) FL (29.1) (28.6) 921.3±31.7 (28.9±0.3) MM (5.1) (6.2) 182.0±25.0 (5.7±0.5) HM 2 nd week TT 40.1 (1.3) 48.0 (1.4) 44.1±4.0 (1.4±0.1) FL (11.1) (9.7) 330.6±7.6 (10.4±0.7) MM (11.2) (11.9) 370.4±28.9 (11.6±0.4) HM (10.7) (10.8) 342.5±16.4 (10.7±0.0) 3 rd week TT 54.0 (1.8) 39.0 (1.2) 46.5±7.5 (1.5±0.3) FL (6.2) (13.4) 319.7±129.7 (9.8±3.6) MM (16.8) (10.9) 437.1±76.6 (13.8±3.0) HM (5.7) (5.7) 183.0±8.0 (5.7±0.0) TT: time trial stage; FL: flat stage; MM: medium mountain stage; HM: high mountain stage. Table II. Time (min) spent in the three intensity zones analyzed in the different stages (mean±sem). Zone 1 Zone 2 Zone 3 Total Time Time Trial 1.2±0.4* 32.5±4.0* 9.2± ±3.2* Flat 124.3± ± ± ±3.1 Medium Mountain 108.1± ± ± ±4.0 High Mountain 113.7± ± ± ±4.8 Zone 1: exercise intensity below ventilatory threshold (VT); Zone 2: exercise intensity between VT and respiratory compensation threshold (RCT); Zone 3: exercise intensity above RCT. *, significant difference with Flat stages (P<0.05)., significant difference with Medium Mountain stages (P<0.05)., significant difference with High Mountain stages (P<0.05). (P<0.05) in the following order: HM (177.3±2.4 km) and MM (174.8±1.9 km), FL (164.0±2.0 km) and TT (26.9±2.5 km). The same trend was observed when stage duration was analyzed (Table II). There were no significant differences (P>0.05) in the maximal HR observed (182±2, 183±1, 182±1 and 186±2 bpm in TT, FL, MM and HM, respectively). However, significant differences (P<0.05) in mean HR between TT (169±2 bpm) vs. FL (135±1 bpm), MM (139±3 bpm) and HM (143±1 bpm), and between FL vs. HM were found. This pattern was also observed for mean HR as a percentage of maximal HR (88.9±0.4, 71.1±0.3, 73.2±0.6 and 75.3±0.4 % in TT, FL, MM and HM, respectively). Session RPE was greater (P<0.05) in HM (7.3±0.2) and MM (7.0±0.3) versus TT (5.5±0.4) and FL (4.6±0.2). The least time (P<0.05) spent in zone 1 was observed in TT (Table II). The time spent in zone 2 increased significantly (P<0.05) with the stage duration (Table II). The only significant differences 156 THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS April 2013

4 Figure 1. Competition load calculated using HR (TRIMP HR ) and session RPE (TRIMP RPE ) and expressed as TRIMP km -1 in the different type of stages analyzed. *significant difference with flat stages (P<0.05); significant difference with Medium Mountain stages (P<0.05); significant difference with high mountain stages (P<0.05). (P<0.05) in the time spent in zone 3 were between mountain stages and FL and TT (Table II). The TRIMP HR and TRIMP RPE followed similar patterns in the different type of stages (Figure 1). The highest (P<0.05) and lowest (P<0.05) TRIMP were observed in mountain stages and TT, respectively. When TRIMP HR and TRIMP RPE were normalized for distance, the lowest value (P<0.05) was found in FL. However, the highest (P<0.05) TRIMP HR km -1 and TRIMP RPE km -1 were found in TT and HM, respectively. Correlations of r=0.62 (P=0.001), r=0.74 (P<0.001), r=0.89 (P<0.001) and r=0.78 (P<0.001) were found between TRIMP HR and TRIMP RPE in TT, FL, MM and HM, respectively. When the exercise intensity pattern throughout the Vuelta a España was analyzed, a decrease and in- crease of the percentage of time spent in zone 2 and zone 3, respectively, was observed from the first to the last weeks (Table III). TRIMP HR and TRIMP HR km -1 analyzed throughout the different weeks were similar in all types of stages (Figure 2). However, when we calculated the TRIMP RPE and TRIMP RPE km -1 significant differences (P<0.05) between the first and third weeks were found (Figure 2). Discussion To date, most studies of professional cyclists have analyzed the exercise intensity by monitoring the HR. 1-6 In the present study exercise intensity was also examined by the session RPE. The main out- Vol No. 2 THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS 157

5 come of this study was that the exercise load during different types of stages can be quantified easily using the session RPE, although the exercise intensity evaluated based on HR or session RPE yielded slightly different results. The highest session RPE was found in the mountain stages (~7.0) followed by TT (~5.5) and FL (~4.5). However, when the mean HR was analyzed, the exercise intensity decreased in the following order: TT (~170 bpm, ~89 %HR max ), mountain stages (~140 bpm, ~74 %HR max ) and FL (~135 bpm, ~73 %HR max ). These differences could be due to the characteristics of TT, where cyclists compete individually and the stages are shorter (~27 km) than the other stages. This characteristic allows the cyclists to achieve a continuous effort. However, in the mass-start stages the work demands are more stochastic due to the terrain, race tactics and the greater length of stages (~170 km). Although, in these stages there are certain situations where the cyclists sustain higher HR (e.g., when the cyclists ascend the mountain passes or when they try to break away from the peloton by attacking or chasing riders attempting to break away). In other situations, HR is lower (e.g., riding downhill or riding in peloton), which influences the mean HR analysis. Therefore, the use of mean HR may not reflect accurately the Table III. Percentage of time spent (mean ± SEM) in the three intensity zones analyzed in the different stages according to the different weeks of 21-day cycling races. Week Zone 1 Zone 2 Zone 3 Time Trial 1 st 1.9± ±9.6* 53.9±9.7* 2 nd 3.2± ± ±5.6 3 rd 2.6± ± ±5.2 mean 2.5±0.7* 62.2±6.2* 35.0±5.6* Flat 1 st 59.1± ±1.8* 6.9±1.2* 2 nd 52.7± ± ±0.9 3 rd 51.2± ± ±0.7 mean 54.4± ± ±0.6 Medium mountain 1 st 40.5± ± ±2.8 2 nd 40.6± ± ±2.2 3 rd 41.9± ± ±1.0 mean 40.9± ± ±1.4 High mountain 1 st 39.6± ±2.8* 13.2±2.6* 2 nd 35.5± ± ±0.9 3 rd 40.4± ± ±0.3 mean 38.2± ± ±1.1 Zone 1: exercise intensity below ventilatory threshold (VT); Zone 2: exercise intensity between VT and respiratory compensation threshold (RCT); Zone 3: exercise intensity above RCT. *, significant difference with 2 nd week (P<0.05)., significant difference with 3 rd week (P<0.05). effort completed by the cyclists. Thus, other methods have been proposed, which establish different intensity zones based on HR response during laboratory tests. 1-6 When we analyzed these zones we found that cyclists spent double time at high intensities in HM and MM compared to TT and FL (Table II). This, together with longer duration of these stages, could influence the session RPE. In addition, we speculate that fatigue affected the cyclists more during mountain stages, for two reasons. First, their location within the overall structure of the Vuelta a España (Table I) and, second, the ascent of mountain passes. Cumulative fatigue in tour races could have more influence in HM and MM by virtue of their positioning during the last weeks of the Vuelta a España, 5 which would bias toward a higher session RPE in these stages. 16, 17 In addition, muscular fatigue may be greater during mountain stages since cyclists ascend mountain passes with hard slopes (7-14%) with low pedaling cadences (70-80 rpm) used to generate high power output (4-5 W kg -1 ). 6, 18 This requires to apply higher forces on the pedals, and may increase the discomfort in the legs, which may increase the RPE. 19 The percentage of time in zones 1, 2 and 3 (Table III) were different from those analyzed by other authors 1, 2 in TT (~5, ~40 and ~55%), FL (~77, ~20 and ~3%), MM 158 THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS April 2013

6 (~74, ~23 and ~3%) and HM (~64, ~27 and ~9%). Overall, our cyclists spent a lower percentage of work at high intensities in TT and HM. However, they spent a greater Figure 2. Evolution of the daily kilometres, session RPE and competition load calculated using the HR (TRIMP HR ) and session RPE (TRIMP RPE ) and expressed as TRIMP km -1 in the different type of stages over the course of the Vuelta a España. *significant difference with 2 nd week (P<0.05); significant difference with 3 rd week (P<0.05). percentage of time in zone 2 and 3 in FL and MM. Potentially this was due to the race strategies used by the cyclists, and to this group of riders being non-contending. Vol No. 2 THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS 159

7 Non-contending riders are not required to work at high intensity on TT and HM stages (which are critical stages for contending riders). These cyclists would tackle these stages with the sole objective of making an effort comfortable enough to be as far ahead as possible, recovering for upcoming stages. Previous studies have analyzed the cyclists efforts during TT 3, 20 and ascent of mountain passes 6, 18 using different race tactics. The higher exercise intensity was analyzed when the cyclists performed all out versus when they used a more conservative approach. 3, 6, 18, 20 The cyclists in this study belonged to a second level team in the UCI (International Cycling Union) classification. The studies by Lucia et al. 2 and Fernández-García et al. 1 were carried out with top-level cycling teams, and contained both single stage and overall winners. Moreover, these teams are composed of domestique riders that help to team leaders or other cyclists who compete for special awards (e.g., king of the mountain, best young riders, special sprints). Also, many times these teams compete to win the best team award (i.e., fastest cumulative time exhibited by a team). Therefore, though in the decisive moments of the race the team leaders perform the greatest effort, the domestique riders also have to perform a major effort in different situations, e.g. in HM these cyclists control the race so that leaders reach the end of stage in the best possible conditions. The primary goal of the team examined in this study was to win stages. Accordingly, cyclists not characterized as good time trialists or climbers took advantage of stages with less topographic difficulty (i.e., FL and MM) by using numerous break away attempts. In the remaining stages (i.e., TT and HM) their goal was to do the least effort possible, which explains the differences in the overall intensity profile compared to other studies. 1-4, 20 Although exercise intensity was significantly different when HR and session RPE were evaluated, the trend for TRIMPs was similar in the different stages (Figure 1). The correlations between TRIMP HR and TRIMP RPE ranged from 0.60 to 0.89 depending of the type of stage. TRIM- P HR values were similar to those previously described ( ) for mass start races by other authors. 5, 21 Higher TRIMP HR in HM ( ) have been observed during the Tour de France 21 more than those analyzed in this and other studies based on the Vuelta a España. 21 These differences were reasonably attributable to the longer duration of Tour de France stages 21 and the higher altitude and length of the mountain passes in the Tour de France. Similarly, the length of the TT analyzed in this study (~27 km) dictated that TRIMP HR was lower (Figure 1) than those found by other authors 20 in contending (~160) and not contending (~120) riders during longer TT (~48 km). Previous studies have expressed the TRIMP according to the competing distance to compare different length races. 22 The TRIMP and TRIMP km -1 pattern observed in this study was different (Figure 1). While the highest total TRIMP was observed in HM, the highest TRIMP HR km -1 and TRIMP RPE km -1 were observed in the TT and HM, respectively. During fatigue states and/or in the presence of muscle damage as observed at the end of 21-day cycling races, 23, 24 HR may not be a good indicator of exercise intensity. Previously a decrease in HR over the course of these races has been observed, 5, 21 which determines the calculated effort exerted by cyclists in different intensity zones. 5 This trend was observed in this study in all types of stages (Table III). We found a decrease in the time spent in zone 3 and an increase in the time spent in zone 2 throughout the race. The increased of time spent in zone 2 could equate to the same TRIMP HR (Figure 2) as has previously been suggested. 20 Likewise, TRIMP HR km -1 analyzed in the different stages were similar during the three weeks of competition (~3.7, ~3, ~2.5 and ~ 2 in TT, HM, MM and FL, respectively). On the other hand, the use of RPE may better indicate of exercise intensity experienced by the athletes in these situations, as an increase in RPE during overreaching has been reported. 16, 17, 25 We found a trend to increase the session RPE throughout the tour in all stages analyzed (Figure 2), which influenced the TRIMP RPE and TRIMP RPE km -1 (Figure 2). Conclusions In conclusion, the present results demonstrate that professional cycling is a highly demanding sport, with exercise intensity and competition load varying according to the type of stage and throughout the Tour. The session RPE method appears to be a valid estimate of internal load during different cycling stage categories. The use of the session RPE may be a more useful tool than HR for calculating the competition load during fatigue states such as those experienced by cyclists at the end of the 21-day cycling races. An improved understanding of the demands of competition is very useful for designing and verifying specific training programs. On the basis of the results of this study, the session RPE method, in addition to being very simple and economic, was a 160 THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS April 2013

8 valid and reliable technique to monitor the training load and exercise intensity in cycling. This is useful because allows coaches to quantify the training load in an easy and non-invasive way. References 1. Fernández-García B, Pérez J, Rodríguez M, Terrados N. Intensity of exercise during road race pro-cycling competition. Med Sci Sports Exerc 2000;2: Lucía A, Hoyos J, Carvajal A, Chicharro JL. Heart rate response to professional road cycling: the Tour de France. Int J Sports Med 1990;20: Padilla S, Mújika I, Orbañanos J, Angulo F. Exercise intensity during competition time trials in professional road cycling. Med Sci Sports Exerc 2000;32: Padilla S, Mújika I, Orbañanos J, Santisteban J, Angulo F, Goiriena JJ. Exercise intensity and load during mass-start stage races in professional road cycling. Med Sci Sports Exerc 2001;33:79Rodríguez-Marroyo JA, García-López J, Juneau CE, Villa JG. Workload demands in professional multi-stage cycling races of varying duration. Brit J Sports Med 2009;43: Rodríguez-Marroyo JA, García-López J, Avila C, Jiménez F, Cordova A, Villa Vicente JG. Intensity of exercise according to topography in professional cyclists. Med Sci Sports Exerc 2003;35: Achten J, Jeunkendrup AE. Heart rate monitoring applications and limitations. Sports Med 2003;33: Foster C, Florhaug JA, Franklin J, Gottschall L, Hrovatin LA, Parker S et al. A new approach to monitoring exercise training. J Strength Cond Res 2001;15: Foster C, Hector LL, Welsh R, Schrager M, Green MA, Snyder AC. Effects of specific versus cross-training on running performance. Eur J Appl Physiol Occup Physiol 1995;70: Impellizzeri FM, Rampinini E, Coutts AJ, Sassi A, Marcora SM. Use of RPE-based training load in soccer. Med Sci Sports Exerc 2004;36: Minganti C, Capranica L, Meeusen R, Amici S, De Pero R, Piacen- tini MF. The validity of session-rating of perceived exertion method for quantifying training load in teamgym. J Strength Cond Res 2010;24: Minganti C, Capranica L, Meeusen R, Piacentini MF. The use of session-rpe method for quantifying training load in diving. Int J Sports Physiol Perform 2011;6: Foster C. Monitoring training in athletes with reference to overtraining syndrome. Med Sci Sports Exerc 1998;30: Davis JA. Anaerobic threshold: a review of the concept and directions for future research. Med Sci Sports Exer 1985;17: Borg GP, Hassmen P, Lagerstrom M. Perceived exertion related to heart rate and blood lactate during arm and leg exercise. Eur J Appl Physiol Occup Physiol 1987;56: Rietjens GJ, Kuipers H, Adam JJ, Saris WH, van Breda E, van Hamont D et al. Physiological, biochemical and psychological markers of strenuous training-induced fatigue. Int J Sports Med 2005;26: Snyder AC, Jeukendrup AE, Hesselink MKC, Kuipers H, Foster C. A physiological/psychological indicator of over-reaching during intensive training. Int J Sports Med 1993;14: Rodríguez-Marroyo JA, García-López J, Villa JG, Córdova A. Adaptation of pedaling rate of professional cyclist in mountain passes. Eur J Appl Physiol 2008;103: Marsh AP, Martin PE. Perceived exertion and the preferred cycling cadence. Med Sci Sports Exerc 1998;30: Earnest CP, Foster C, Hoyos J, Muniesa CA, Santalla A, Lucía A. Time trial exertion traits of cycling s grand tours. Int J Sports Med 2009;30: Lucía A, Hoyos J, Santalla A, Earnest C. Tour de France versus Vuelta a España: Which Is Harder? Med Sci Sports Exerc 2003;35: Rodríguez-Marroyo JA, Pernía R, Cejuela R, García-López J, Llopis J, Villa JG. Exercise intensity and load during different races in youth and junior cyclists. J Strength Cond Res 2011;25: Lucía A, Díaz B, Hoyos J, Fernández C, Villa G, Bandrés F, Chicharro JL. Hormone levels of world class cyclists during the Tour of Spain stage race. Brit J Sports Med 2001;35: Mena P, Maynar M, Campillo JE. Changes in plasma enzyme activities in professional racing cyclists. Brit Sports Med 1996;30: Martin DT, Andersen MB. Heart rate-perceived exertion relationship during training and taper. J Sports Med Phys Fitness 2000;40: Vol No. 2 THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS 161