Research Paper PrePrint – A comparison of the metabolic cost of the three phases of the one-day event in female collegiate riders

Research Paper PrePrint – A comparison of the metabolic cost of the three phases of the one-day event in female collegiate riders 

Authors: Marcus Roberts 1 , Jeremy Shearman 2# and David Marlin 3 *
Affiliations: Writtle College, Writtle, Essex, Department of Biological Sciences, University of Essex, Colchester, UK. Hartpury College, Hartpury, Gloucester, UK. Animal Web Ltd, Cambridge, UK

Abstract

Few studies exist regarding the physiological responses of equestrian riders during actual or simulated competition. Interest has proliferated in recent years into the responses of riders which is mainly due to the fatal tragedies that occurred in eventing in the late 1990’s. More emphasis is also being placed on the importance of rider fitness in order to improve athletic performance at International level. The aim of the present study was to investigate the fitness and exercise capacity of female equestrian athletes and to relate this to the metabolic requirements of dressage, show jumping and cross county phases of the one-day event. Sixteen female collegiate riders (age = 24.5±7.7 years; ht = 166.6±3.8 cm; wt = 60.4±6.0 kg) competed in a simulated Horse Trials Pre Novice competition riding either their own horse or one familiar to them. Anthropometric data was obtained for each rider (BMI = 21.7±1.9; %BF = 23.4±5.3; LBM = 48.5±3.6%). Each subject successfully completed all three phases of the event. There was a progressive increase in oxygen consumption (VO₂) during the 3 phases (DR, SJ and XC) from a mean value of 20.4±4.0 ml.kg^-1.min^-1 (DR), 28.1±4.2 ml.kg^-1.min^-1 (SJ) to 31.2±6.6 ml.kg^-1.min^-1 (XC)(P<0.001). HR data showed a similar trend from a mean value of 157±15 b.min^-1 (DR), 180±11 b.min^-1 (SJ) to 184±11 b.min^-1 (XC) (P<0.001). Mean lactate concentration increased progressively from resting values; rest 2.5±1.3 mmol, DR 4.8±1.8 mmol, SJ 7.8±2.4 mmol and XC 9.5±2.7 mmol (P<0.001). Urine osmolality was significantly (P<0.001) increased from a pre competition mean of 0.488±0.270 mOsmol/l to a post competition mean of 0.684±0.230 mOsmol/l. Mean hand grip strength was observed to decrease significantly (P<0.01) from a pre value of 32.3±6.3 kg to a post value of 29.8±5.5 kg. Mean weight loss pre to post-competition was 1.6±1.1 % bodyweight (P<0.01). In conclusion, the study emphasises the variability in metabolic cost between riders performing in the same simulated competition but riding different horses highlights the difference in metabolic demand between the different phases.

Introduction

Horse Trials (Eventing) originally evolved from the training of cavalry horses. The sport is rather like the pentathlon in that it combines different disciplines in one competition and is run on a cumulative penalty basis. The sport of eventing is a great all round test of horse and rider and a tremendous examination of horsemanship and is renowned for being one of the most challenging equestrian sports for both horse and rider (Phillips, 1999). The one-day event (ODE) is a three phase competition. Phase one is the dressage (DR) test that comprises a set sequence of compulsory movements at a relatively low speed in an area 20 meters wide and 40 meters long (60 metres at higher levels of competition). Phase two is the show jumping (SJ) test where the horse and rider combination is required to complete one round of jumping over approximately nine/ten coloured fences within a set time. Phase three is the cross country (XC) test, in which the horse and rider negotiate a series of solid natural obstacles while galloping across country (Paix, 1999).

Horse riding is considered to be a particularly dangerous sport (Whitlock et al. 1987; Whitlock, 1999; Ball et al. 2007). The sport of Eventing in particular was brought under the scrutiny of the public eye in 1999 for negative reasons. Five riders were killed at separate events during the season, and the sport has been put under pressure to investigate the accidents and improve safety for both the horse and rider. These tragedies has forced the immediate revision of all possible factors, which might have had a part in the tragic events in order to prevent similar accidents from occurring in the future. Among those reasons suggested as a potential contributing factor for the recent tragedies is the fitness and competence of the equestrian rider. In 2007, following another spate of deaths in eventing with 7 riders dying in a period of 10 months, the governing body of World equestrian sport, the Federation Internationale Equestre (FEI), launched a review of safety (Horse and Hound, 17^th May, 2007).

In the interest of the horse, the fitness and competence of the rider is regarded as essential (American Medical Equestrian Association (AMEA), 2001). “A tired horse will be hindered by a tired rider” (Chiacchia, 2001). The equestrian athlete spends many hours each week assuring proper nutrition, exercise, training and excellent medical care is provided for their horse. However, many riders overlook these important areas for themselves.

A large amount of literature exists on the technique of riding, and on the anatomy and physiology of the mammalian body and the effects of exercise and consequently training of the physiological systems of the general athlete. Physical fitness is required by the equestrian athlete for maintenance of balance and effectiveness but scientific research into the physiological demands of horse riding is very limited, especially considering the diversity of disciplines now popular within the sport.

Gutierrez-Ricon et al., (1992) monitored the heart rate and lactate profiles in 3 elite equestrian athletes and their horses during the SJ phase of the Olympic Three Day Event to ascertain the metabolic cost of that discipline. HR measurements indicated that jumping in competition involved a work rate of above 90% maximal HR. An increase in lactate production was observed above that of lactate threshold (4-8 mmol/L) suggesting that there is a local metabolic build up during the short period of exercise. Both HR and lactate levels were higher in the riders than in their horses, suggesting that the metabolic cost of the rider was higher than that of the horse.

Perhaps one of the most useful guides to the physical demands of riding is the work of Westerling (1983) who studied thirteen experienced and three elite equestrian athletes during submaximal and maximal bicycle ergometer exercise and during a ridden test. The HR/O₂ uptake relationships were similar at the same workload in the ridden and cycle ergometer tests, although HR tended to be higher in sitting trot. During canter, the experienced riders were found to be working at over 60% maximal aerobic power, an intensity at which some training effects would be expected. Interestingly, static muscle strength did not differ significantly between the rider group and control group.

Trowbridge, et al., (1995) reported on the physical demands of riding in National Hunt racing in the UK, an event which has some similarities to the XC phase of the three day event. Seven male jockeys were used in the study over 30 races. Average HR ranged between 137 and 178 beats min^-1, and peak HRs were 162 – 198 beats min^-1. Post race blood lactate concentrations ranged from 3.5 – 15.0 mmol/l. These findings suggest that National Hunt racing requires the jockeys to be both aerobically and anaerobically fit, as indicated by the high HR and peak lactate results.

The physical and haematological responses to exercise of 24 collegiate female equestrian athletes was reported by Meyers and Sterling (2000). BMI and LBM fell within reported athletic norms for females although % BF was above average in the riders. Mean VO_2max, VE_max and hand grip strength were lower in the riders when compared predicted values for female athletes competing in other sports. It was concluded that a lack of adequate physical conditioning of the equestrian athlete could be a contributing factor in the growing trend in injuries. In general riders when compared to athletes in other sports possessed below average aerobic power, anaerobic capacity, and muscular strength, with an above average %BF

Devienne and Guezennec, (2000) measured the energy expenditure of horse riding in 5 experienced riders. There was no statistical difference between the riders riding known and unknown horses. It was concluded that energy expenditure increases significantly during riding and “a good aerobic capacity appears to be a factor determining riding performance in competition. Regular riding and increased physical rider training were recommended to enhance physical fitness of competitive equestrian athletes.

The aim of the present study was to describe the physiological responses and metabolic cost of the different phases of eventing in a simulated competition. Our hypothesis was that there would be variation in metabolic demand between different riders and within the same rider over the different phases.

Materials & Methods

Subjects
Sixteen female volunteer subjects (n=16) who engage in regular equestrian events were used in the study. The riders were of mixed ability and experience (10.6 ± 3.7 years riding), however all were capable of completing a Pre Novice level one day event. Only 6 subjects had previously competed at this standard under British Eventing affiliation. Prior to the test, all subjects were informed of the aims and the essential characteristics of the investigation. Informed consent was obtained in accordance with guidelines established by the University of Essex, Biological Sciences Department. Anthropometric data was collected from each subject including height, weight, skinfolds, girths, bone lengths, and breadths as indicated in the ISAK level II anthropometry procedure. Individual measurements were repeated three times and the mean for each measurement was calculated. The data was entered into Lifesize software (University of South Australia) for further analysis.

Protocol
Each subject was required to complete a simulated one-day event (ODE) held at Writtle College Equine Training and Development Centre. The ODE was designed to mimic a British Horse Trials Association (BHTA) Pre-Novice competition, comprising a DR, SJ and XC phases. The DR test used was Horse Trials 112 and was performed in an indoor riding arena measuring 20 x 40 meters. The SJ course was performed in an outdoor manege which measured 25 x 65 meters and consisted of 9 jumping efforts and measured 370 meters. The show jumps range between 0.95 and 1.0 meters in height. The XC course consisted of 19 jumping efforts and measured 1553 meters in length. The maximum height of the XC fences was 1.00 meters. All three phases were designed using the BHTA guidelines and rule book. Each rider rode a horse that they were familiar with and that was considered capable of competing in all 3 phases. The subjects were asked to warm up the horse for each phase as they would at a competition, before commencing each phase. All subjects were required to wear appropriate back protection throughout the SJ and XC phases. The time taken to complete each individual phase was recorded using a hand held stopwatch.

Gas Analysis
Measurement of oxygen uptake, carbon dioxide output, and RER were recorded using the Metamax 3B (MMX3B 1.0, Leipzig, Germany) analyser continuously throughout all three phases of the ODE. The subjects wore a small face-mask which enabled them to breathe through a volume transducer fixed to the face mask. The battery was connected to the Metamax 3B to allow self contained measurements to be taken during the exercise protocol. The Metamax 3B was secured to the subjects using the Maxbelt (velcro scarf to hold the metamax in place) to prevent excessive movement while riding exercise took place. After fitting of the Metamax 3B system was complete data collection commenced prior to the rider mounting the horse. A marker was used to identify precisely the start and end point of each phase. The equipment was calibrated before and after recordings on each rider according to the manufacturer’s instructions using air (20.95% O₂ and 0% CO₂) and a certified gas mixture (approximately 18% O₂ and 3% CO₂).

The gas parameters and RER estimates were collected and calculated as mean values for each 10 seconds. All data recorded was stored in the internal data logger for subsequent downloading into the personal computer. Mean VO₂ for each subject throughout each phase was calculated together with the overall mean for all subjects for each phase of the event. The average O₂ uptake (L/min^-1) was calculated for every 10 seconds for all subjects during each phase of the ODE. Mean energy expenditure (kcal/min) for each phase was calculated using the following formula: Kcal = VO₂ (l/min) x RER calorific equivalent (kcal/l). %VO_2max was calculated as previously described (Meyers and Sterling, 2000).

Heart rate (HR)
Heart rate was recorded throughout the three phases of the ODE using a Polar Advantage NV HR monitor (Kempele, Finland) in 5 second averaging mode. A saline solution was used to improve the conductivity between the skin and the electrodes. Markers were entered into the watch corresponding to the start and end of each phase. Maximal HR was estimated from the equation (220 – age) in order to calculate relative workloads (% HRmax).

Lactate
Blood lactate concentrations ([LA]_b) were determined using an Analox P-GM7 lactate analyser (Analox Instruments, Hammersmith, London, UK) calibrated according to the manufacturer’s instructions using an 8mmol/l calibration solution and a quality control solution in the range 2.3-2.7 mmol/l. The coefficient of variation for this equipment on capillary blood has been reported to be 7% (Godfrey et al. 2009). Capillary blood lactate measurements were taken at rest and at 1 minute after all three disciplines. The puncture site (finger tip) was disinfected using an alcohol impregnated swab. A sterile automatic lancet was used to puncture the finger tip and the needle disposed of hygienically after each use. The first drop of blood was discarded and the second collected using a Heparinised Capillary/Lysing Microtubule Blood Collection System (GMRD-070) (Hammersmith, London, UK). Each individual microtube was immediately stored at below 0^oC in preparation for analysis.

Urine Testing
The Osmomat 030 (Gonotec, Germany) was used to determine the total osmolality of the subjects urine immediately before and after the event. Each subject was asked to collect the urine midstream and samples were sealed and refrigerated until analysis was undertaken. Prior to testing urine the Osmomat 030 was calibrated using 50µl distilled water followed by a second calibration using 50µl calibration solution. In order to check measurement reproducibility, two measuring vessels were filled (50µl) with the same sample solution and measured sequentially. The reported intra and inter-assay coefficient of variation for urine from female subjects for this equipment when used according to manufacturer’s instructions have been reported to be 1.5% (MacLeod and Sunderland, 2009).

Strength Testing
A hand held dynamometer was used to obtain hand grip strength immediately before the DR phase and 1 minute after the XC phase. Whilst seated, subjects were asked to hold the dynamometer in the right hand with a straight arm above their head, and grip the handle as hard as possible while lowering their arm down their side.

Weight measurement
The weight (kg) of each equestrian rider was obtained before and after the event using a digital portable weigh machine. Subjects were asked to remove their clothes and towel dry before the weight measurement was taken.

Data Analyses
All VO₂, HR, blood lactate, urine osmolality and strength values are expressed as mean and standard deviation (±SD). Statistical analysis was performed using Statistical Package for Social Science (SPSS) for windows version 10.0. A one factor within subjects ANOVA was used to determine significant difference between mean and peak VO₂ and HR and mean post exercise blood lactate concentrations between the three phases of the event. Post Hoc differences were tested by paired samples t-test. The bonferroni procedure was used to calculate the acceptable level of significance. A paired t-test was also used to investigate differences between pre and post urine osmolality and hand grip strength.

Results

General
The physical and other characteristics of the riders are shown in Table 1. All sixteen female riders who took part in the study successfully completed all three phases of the event. The mean times and speeds to complete each phase are presented in Table 2.

Oxygen Uptake
Mean and peak oxygen consumption is shown in Table 3 and increased progressively with each phase from DR to SJ to XC. The XC phase produced the highest mean estimated %VO_2max of 93 ± 19 in comparison to the SJ phase (83 ± 12 %VO_2max) and DR phase (60 ± 12 %VO_2max).

Heart Rate
A similar trend for heart rate to that for oxygen uptake was observed. The XC phase produced the highest mean (184 ± 11 bpm) and peak (190 ± 11 bpm) heart rates, followed by the SJ phase (mean 180 ± 11 bpm; peak 188 ± 11) with the DR phase producing the lowest mean (157 ± 15 bpm) and peak (172 ± 15 bpm) heart rate. Mean and peak heart rate was significantly different for each phase (ANOVA P<0.001).

Energy Expenditure
During the event the dressage phase required the lowest Estimated energy expenditure was significantly lower during the DR phase (5.9 ± 1.0 kcal/min^-1 ;P<0.01) compared with the SJ and XC phase (8.2 ± 1.1 and 8.5 ± 1.1 kcal/min^-1, respectively). Mean total energy expenditure required for each phase was estimated to be 31.1, 15.4 and 41.0 for the DR, SJ and XC phases, respectively.

Lactate Concentration
Blood lactate concentration increased progressively over each phase of the competition (Figure 1) reaching a mean of 9.5 ± 2.7 mmol/l.

Urine Analysis
A significant increase (29%) was observed in mean urine osmolality following the XC phase (0.684 ± 0.23 mOsm) compared with before competition (0.488 ± 0.27 mOsm; P<0.001).

Hand Strength
Mean hand grip strength decreased significantly following competition (29.8 ± 5.5 kg) compared with before competition (32.3 ± 6.3 kg ; P<0.001)

Bodymass
Mean bodymass change with the competition was 1.0 ± 0.8 kg (P<0.01) and ranged from 0.0 to 3.5kg. This represented a % bodymass change of 1.6 ± 1.1%.

Discussion

The purpose of this study was to quantify the physiological responses of female equestrian athletes in order to provide a greater insight into the demands of eventing and to compare the results with similar studies and other sporting athletes. The study also highlighted variability in the riders metabolic cost according to the phase being performed.

The anthropometric data suggests that the mean % body fat of the subjects in the current study fell within the average category as described by Morrow, et al., (1995). However, in comparison to Meyer and Sterlings, (2000) the subjects in the present study had a lower % body fat than other equestrian athletes. The mean % body fat in this study was higher than reported values for female athletes competing in other sports events such as swimming (10 – 18 %BF), tennis (10 – 20 %BF), sprinting (19.3 %BF), cross country skiing (10 – 18 %BF) and distance running (15.2 – 19.2 %BF). However, values were within the range for female volleyball players (21.3 – 25.3%BF) but lower than values reported for female shot put players (28.0 %BF; Powers and Howley, 2001). A high %BF in athletes has been shown to have a negative effect on the health of an individual and decreases performance in many sports that require endurance, flexibility and agility (Wilmore and Costill, 1994), which have been highlighted as essential attributes for the equestrian athlete (AMEA, 2001). Subject 7 was observed to have the highest %BF (37.3) and interestingly was recorded to have the highest HR values in all three phases. The reported relatively high %BF values in the current study observed among the equestrian athletes, highlights concerns regarding the lack of physical conditioning of the subjects who took part in the trial when compared to established norms in other sports.

Mean BMI of the subjects in the present study were within the desirable range of 20.0 – 24.9 (ACSM, 1995) and was observed to be similar to the BMI of other female equestrian athletes (24.8 ± 1.7) reported by Meyers and Sterling (2000). The mean LBM of the subjects was similar to that reported in collegiate equestrian athletes (49.0 ± 4.5 kg; Meyers and Sterling (2000).

Devienne and Guezennec (2000) reported that as pace progressed from walk through trot and to canter, so to did the energy demand and therefore oxygen consumption.

The high heart rates and high estimated %VO2max (>90%) indicate that the one day event required a high cardiovascular effort. A potential limitation of this study is that whilst heart rate and oxygen consumption were both measured, VO_2max was only estimated. Whilst on a population basis this is appropriate it could lead to considerable error when looking at the response of individual riders. It has been reported that continuous physical exercise at 60 – 70 % VO_2max for several 30 minute sessions per week enhances aerobic capacity (McArdle, et al., 2000).

The energy expenditure of the equestrian athletes during the DR was observed to be similar to that expended by female athletes cycling at 16.1 km/hr and comparable to sports such as walking (3.9 kcal.min^-1) and tennis (5.5 kcal.min^-1)(Wilmore and Costill, 1994). The rates of energy expenditure during the SJ and XC phase were comparable to female sporting activities such as basketball (6.8 kcal.min^-1), weight lifting (6.4 kcal.min^-1) and wrestling (10.3 kcal.min^-1) (Wilmore and Costill, 1994). However, the riders canter and jump for only a small part of a normal training session, with the majority likely consisting of walking and trotting. Although limited time is generally spent in the jumping phase during training which subsequently minimises the training response, riding at this intensity is reported to be at a metabolic cost capable of producing a general fitness level similar to that produced by aerobics or gymnastics (Devienne and Guezennec, 2000).

During the event the [LA]_b increased progressively during the three phases. The results are in agreement with the work of Gutierrez-Ricon (1992), who reported blood lactates of 5.0 – 6.3 mmol/l during SJ competition, and also compares with the findings of Trowbridge, et al., (1995), who found a mean [LA]_b of 7.1 mmol/l in jockeys following National Hunt racing.

The higher physiologic demands of the SJ and XC phases may be due to the forward position adopted over and between the fences, which requires strength and good muscle control in the legs, back and arms. Also body movement, to absorb movement of the horse, particularly over fences when the position is modified to remain in balance with the horse, and the actions of the legs and arms in giving aids to the horse, are similar in many ways to National Hunt race riding (Trowbridge, et al., 1995). Riding position during DR differs from the SJ and XC phases as the rider tends to sit more upright, with their weight supported by the horses back rather than by the riders legs. This may contribute to the lower physiological demand than in the two jumping phases.

The blood lactate values at the end of the SJ phase are similar to those in the 110m hurdles (7.0 mmol/l; Beaulieu, et al., 1995) and in rugby players (5.8 – 9.8 mmol/l; McLean, 1992) whereas the concentrations following the XC are similar to those following a 100m sprint (12.1 mmol/l; Beaulieu, et al., 1995) and speed skating (9.8 mmol/l; Rundell, 1996).

Mean urine osmolality increased significantly after completion of the event. Although still within acceptable limits, the osmolality values reported indicate that the riders became dehydrated during the ODE. Dehydration may invoke physiological responses such as the redistribution of body fluids with changes in hydrostatic and osmotic pressure. The gradual onset of dehydration may have implications for the rider that has multiple horses to be ridden or competing on the same day. In addition to the actual time spent in the saddle, the rider will be required to prepare the horse, walk the SJ and XC course (sometimes twice) which all add to the metabolic cost of the event. Mean fluid loss corresponding to 1.6 ± 1.1 % BW was observed in the current study. Armstrong, et al., (1985) reported that a reduction in body mass by 1.5 – 2.0% results in a decrease in performance by up to 6.3 %. Two subjects lost 2.5 and 4.6 % bodymass throughout competition. Nielsen, et al., (1981) found that weight loss of this extent resulted in a 45% decrease in the capacity to perform high intensity exercise lasting about 7 minutes. This may cause a lack of ability of the rider to concentrate and help a tired horse towards the end of the XC phase and could be a potential contributory factor in the occurrence of accidents.

A mean decrease in strength was observed after the three phases of the ODE suggesting a degree of fatigue post competition. A lack of strength may have implications for the rider who has several horses to ride at one event and may cause a reduction in their effectiveness on subsequent horses if time to recover in between phases or rides is insufficient. Therefore it may also be appropriate for riders to introduce strength training into their aerobic conditioning programme to reduce the onset of fatigue during training or competition riding.

In conclusion, the study emphasises the variability in metabolic cost between riders performing in the same simulated competition but riding different horses. There is also a difference in metabolic demand between the different phases. The data support a requirement for equestrian athletes to undertake supplemental training in addition to riding to increase strength and aerobic fitness.

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Measurement	Mean Value	Range
Age (years) Height (cm) Weight (kg) BMI (weight/height2) Body Fat (%) LBM (kg)	24.5 ± 7.7 166.6 ± 3.8 60.3 ± 5.8 21.7 ± 1.9 23.4 ± 5.3 48.5 ± 3.6	17 – 44 161.5 – 175.6 49.2 – 76.6 18.8 – 26.4 15.6 – 37.3 40.7 – 55.2

	Dressage	Show Jumping	Cross Country
Mean time (minutes)	4.43 ± 0.51	1.88 ± 0.28	4.79 ± 0.51
Mean speed (meters per min)	146 ± 17	201 ± 32	327 ± 33

	Dressage	Show Jumping	Cross Country
	Mean	Peak	Mean	Peak	Mean	Peak
O2 Consumption (ml.kg-1.min-1)	20.4 ± 4.0*	28.6 ± 6.2#	28.1 ± 4.2*	34.7 ± 6.3#	31.2 ± 6.6*	37.9 ± 7.4#

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