Body composition in young Standardbreds in training: relationships to body condition score, physiological and locomotor variables during exercise

REASONS FOR PERFORMING STUDY

Body composition is an essential factor in athletic performance of human sprinters and long distance runners. However, in horses, many questions remain concerning relationships between body composition and performance in the different equine activities.

OBJECTIVES

To determine relationships between body composition, body score, physiological and locomotor variables in a population of young Standardbreds in training.

METHODS

Twenty-four 2-year-old Standardbreds were studied, body condition on a scale 0-5 and bodyweight recorded, and height at withers measured. Percentage of fat (%F), fat mass (FM) and fat free mass (FFM) were estimated echographically. During a standardised exercise test on the track, velocity, heart rate, respiratory frequency and blood lactate concentrations were measured. V4 and V200 (velocity for a blood lactate concentration of 4 mmol/l and velocity of 200 beats/min) calculated. Basic gait variables were measured at 3 different speeds with an accelerometric device.

RESULTS

Body composition variables: %F and FM were significantly related to body condition score and physiological variables. Body score was highly correlated to %F (r = 0.64) and FM (r = 0.71). V4 was negatively correlated to %F (r = -0.59) and FM (r = -0.60), P<0.05. V200 was also negatively related to %F and FM, (r = -0.39 and r = -0.37, respectively, P<0.1). No relationships were found between body composition and gait characteristics.

CONCLUSIONS

Body composition was closely related to indirect measurements of aerobic capacity, which is a major factor of athletic performance in middle distance running horses.

POTENTIAL RELEVANCE

As in human athletes, trainers should take special note to evaluate optimal bodyweight and body composition of race horses to optimise performance.

Factors influencing variation in locomotor-respiratory coupling in Standardbred Trotters in the field

REASONS FOR PERFORMING STUDY

A close relationship between limb and respiratory rhythms has been shown in clinically healthy galloping horses due to mechanical constraints in the thoracic region. This synchronisation leads to a 1/1 ratio between stride frequency (SF) and respiratory frequency (RF) during galloping. Very little is known about locomotor-respiratory coupling (LRC) during fast trot.

OBJECTIVES

To investigate stride and respiratory rates during a standardised exercise test on the track in Standardbred Trotters.

METHODS

Forty-four French trotters age 2-10 years performed a standardised exercise test consisting of three 3 min steps at constant speeds. Speed (V) of exercise varied between 500 and 750 m/min. Variables measured during exercise: SF, heart rate, RF using a microphone between the nostrils, blood lactate concentration. Physiological variables V4 and V200 were calculated and race performance index recorded.

RESULTS

There was no age-related difference in RF or in LRC. Two LRC strategies were found: around 1/1 ratio and 3/2 ratio between SF and RF, respectively. A relationship between SF/RF ratio and physiological parameters showed a higher LRC in good performers because of a lower RF during submaximal and maximal exercise.

CONCLUSION

RF is significantly lower and LRC significantly higher in good compared to poor performers.

POTENTIAL RELEVANCE

Investigation is required to ensure that the breathing techniques of trotters may be used in the selection process of racehorses.

Harnessed vs. mounted standardbreds on the track: changes in gait and physiological variables

REASONS FOR PERFORMING STUDY

It has become apparent through analysis of elite races over the past 20 years that mounted races are always slower than harnessed races when performed by the same horses over the same distances on the same tracks.

OBJECTIVES

To investigate and compare physiological and gait variables in mounted and harnessed activities in trotters.

METHODS

Ten trotters were taken at random in 2 standardised field exercise tests one week apart: a harnessed and a mounted test with standardised weight jockeys and drivers. Speed, heart rate (HR), respiratory frequency (RF), blood lactate concentration (La), stride characteristics (length, frequency [SF], symmetry, regularity, dorsoventral displacement of the sternum and vertical, longitudinal and lateral activities measuring the amount of deceleration and acceleration along the 3 axis) were measured.

RESULTS

Paired t tests and an analysis of variance were calculated between the 2 conditions and revealed that V4 (speed for a La of 4 mmol/I), V200 (speed for a HR of 200 beats/min), stride length, trot symmetry, lateral activity were lower in the mounted condition. In contrast, RF, SF, dorsoventral displacement, vertical and longitudinal activities were significantly higher in mounted horses compared to harnessed horses.

CONCLUSION

The significant physiological and biomechanical differences between pulling whilst harnessed and being ridden reflect an increase in the energy requirement of locomotion in the mounted condition compared to the harnessed condition. Trotting mounted at maximal speed is more demanding for the horse than harnessed as reflected by the lower V4 and V200 and some gait variables change in relation to this phenomenon.

POTENTIAL RELEVANCE

This study demonstrates that trotting mounted at sub-maximum and maximum speed is more demanding for the horse when ridden and that it modifies some gait variables, either as a result or even as a possible cause.

Optimal active recovery intensity in standardbreds after submaximal work

REASONS FOR PERFORMING STUDY

A retrospective study concerning spontaneous active recovery intensity, i.e. at a freely chosen speed, after a submaximal exercise in trotters showed that the mean intensity demanded by trainers corresponds to 40-50% of maximal heart rate (max HR; unpublished data). However, in human athletes, optimal active recovery intensity was found to be about 60-70% of max HR. Is the spontaneous recovery optimal after a submaximal exercise in trotters?

OBJECTIVES

To compare different recovery intensities and define the most efficient one.

METHODS

Thirty-seven trotters performed a standardised exercise test on the track. Horses were randomly divided into 4 groups of recovery: passive recovery (n = 10), 10 min walk recovery (n = 10, 100 m/min), 10 min slow trot recovery (n = 9, 250 m/min) and 10 min fast trot recovery (n = 8, 420 m/min). Before, during and 1 h after exercise, speed, heart rate, blood lactate concentration were measured as well as respiratory frequency and rectal temperature. Creatine kinase (CK) was measured 1, 3 and 5 h after exercise.

RESULTS

Walk, slow trot and fast trot recovery corresponded respectively to 45-50%, 55-60% and 65-70% of max HR. Heart rate and blood lactate concentration were significantly lower after the 10 sec recovery with increasing intensity of recovery.

CONCLUSION

The most efficient intensity of recovery was the 10 min fast trot recovery (65-70% max HR) as this type of recovery allows the optimal blood lactate disappearance.

POTENTIAL RELEVANCE

Considering the usual habits of trainers or drivers, recovery intensity after trot races should be increased in intensity to optimise its efficiency.

Effect of age on locomotion of Standardbred trotters in training

In Standardbreds, the main aim of early training (begun during the growth period) is the mechanization of athletes leading to a particular gait called the ‘flying trot’. The present cross-sectional study was undertaken to investigate the biomechanical and physiological factors involved in this gait change, and aimed to analyse the effect of age on gait and energetic variables in a population of Standardbred horses under training. One hundred and forty-three horses aged from two to seven years were tested on a track at three speeds (8.5, 10 and 11.6 m s−1) with a gait-analysis system. Gait variables (temporal and linear variables, symmetry, regularity, two-beat rhythm, dorso-ventral, longitudinal and lateral activities) were compared between four age groups (two-, three-, four-, and five-year-olds and above). After a standardized exercise test, two energetic variables (V4 and V200) were also compared between these groups. Most variables were influenced by age/training status. The results indicated that, from young to mature racehorses, stride length and duration increase; and gait becomes more symmetric and more regular. We also observed a decrease in dorso-ventral, longitudinal and lateral activities, i.e. a decrease of thoracic displacements. These differences could be elucidated at slow speed and were still obvious at high speed. V4 and V200 also increased significantly with age/training status. All of these results indicate an improvement in co-ordination and a decrease in metabolic cost with increasing age/training status. Thus gait acquisition could be related to an improvement in trotting efficiency.

Relationships between physiological variables and race performance in French standardbred trotters

The relationships between V4 (the velocity for a blood lactate concentration of 4 mmol/litre) and V200 (the velocity for a heart rate of 200 bpm) and the performance indices of 223 healthy French trotters were analysed. They were divided into four age groups of three, four, five and six years and over, and into three performance groups (good, intermediate and poor performers) defined by the index of trot (ITR), an annual index of performance calculated by the national stud. V4 and V200 were assessed during the performance of a three-step standardised field exercise test, and four performance indexes (ITR, earnings, best time and the number of starts) were calculated for each group. An analysis of variance showed that V4 and V200 were highly correlated with the horses' age and level of performance (P<0.05). The correlation between the physiological variables and ITR was better for the three- and four-year-old horses than for the older horses.

Reproducibility of a locomotor test for trotter horses

Locomotion analysis is increasingly used to assess the gait of horses in the selection and training of equine athletes. We have developed a specific locomotor test for fast trotting harnessed horses that uses an accelerometric device. We describe here the reproducibility of the locomotor test and the validation of its use to analyse trotters on the racetrack. We measured the performance of eight horses under the same conditions three times in a single week. We then tested the influence of five tracks on the variables measured using eight different trotters every two days. The horses trotted at three or four velocities (8.3, 10, 11.7 m/s and at maximal velocity) in a straight line for 20 s. The short-term reproducibility of the test was very good for 23/25 variables, with no significant difference in the 23 variables for the three measurements. The two less reproducible variables reflected human error. The different tracks did not alter the stride variables measured. We conclude that the test is an easy, accurate method for analysing gait, as it provides reproducible stride variables for trotting harness horse under field conditions.

[Structure-activity relationship of semi-synthetic derivatives of the PIA component of pristinamycin]

Pristinamycin is a naturally occurring streptogramin made up of 2 groups of synergistic components (PI and PII). Because these components are not water soluble, use of pristinamycin has up till now been confined to the oral route. Water soluble semisynthetic derivatives of the PIA component, appropriate for parenteral use, have lately been developed. PIA is a peptidic macrolactone. As opening of the lactone results in total loss of biologic activity, semisynthesis must spare this function and preserve the macrocycle. Reactions at 5 gamma and 5 delta yielded 4 families of derivatives. Antimicrobial activity has been studied for more than 80 compounds. Several derivatives are promising as they are water soluble and have in vitro and in vivo (mice) activities similar to those of the original PIA component.