Differences in the metabolic properties of gluteus medius and superficial digital flexor muscles and the effect of water treadmill training in the horse

Blood flow restriction training does not negatively alter the mechanical strength or histomorphology of uninjured equine superficial digital flexor tendons

BACKGROUND

Low load exercise training with blood flow restriction (BFR) has become increasingly used by human physical therapists to prescribe controlled exercise following orthopaedic injury; its effects on the equine superficial digital flexor tendon (SDFT), however, are unknown.

OBJECTIVE

To investigate outcomes of pressure specific BFR walking exercise on uninjured equine SDFT biomechanics and histomorphology.

STUDY DESIGN

Controlled in vivo experiment.

METHODS

Four forelimbs of four horses were exposed to 40 BFR-walk sessions (10-min interval walking) on a treadmill over a 56-day study period with their contralateral forelimbs serving as untreated controls. Similarly, four forelimbs of four control horses were exposed to 40 sham cuff walk sessions. On study Day 56, all horses (n = 8) were humanely euthanised and forelimb SDFTs underwent non-destructive biomechanical testing and corresponding histomorphological analysis. Significance in biomechanical parameters between treatment groups was analysed using a mixed-effects ANOVA with Tukey's post-hoc tests.

RESULTS

Statistically significant differences in SDFT stiffness for both first (p = 0.02) and last cycles (p = 0.03) were appreciated within the BFR treated group only, with BFR exposed forelimbs being significantly stiffer than the contralateral unexposed forelimbs. When normalised to cross-sectional area, no significant differences were appreciated among treatment groups in elastic modulus for the first (p = 0.5) or last cycles (p = 0.4). No histological differences were appreciated among treatment groups according to Bonar, Movin, or musculotendinous junction evaluation criteria.

MAIN LIMITATIONS

Short-term comparisons were performed in a small sample population without correlation to performance outcome measures. Optimal occlusion percentages and walk protocols remain unknown.

CONCLUSIONS

This study demonstrated no negative impact of BFR on mechanical strength of the equine SDFT; however, evidence suggests that BFR results in increased tendon stiffness based on biomechanical testing and subsequent calculations. No consistent detrimental histomorphological changes were seen.

Effect of speed and water depth on limb and back kinematics in Thoroughbred horses walking on a water treadmill

Water treadmill (WT) exercise may induce limb and back kinematics that meet specific training and rehabilitation goals. The study aimed to investigate the effects of walk speed, at different water depths (WDs), on limb and back kinematics of six Thoroughbreds exercising on a WT. Horses walked at 2.8/4.3/5.5/6.0 km/h (i.e. 0.8/1.2/1.5/1.7 m/s) at dry, metacarpophalangeal and carpal WD. Videography captured limb movement in the sagittal plane. Motion-capture measured thoracolumbosacral flexion-extension (FE), and lateral bend (LB) ranges of movement (ROM) using skin surface markers on the sixth, tenth, thirteenth, eighteenth thoracic, third and fifth lumbar, and third sacral spinous processes. Inertial-motion-sensors measured poll, withers and pelvic displacements. Following preliminary univariable analyses, multivariable mixed-effects linear-regression analyses were used to examine the relationship between speed, WD and each outcome variable (P < 0.05). Peak metacarpophalangeal, carpal and tarsal joint flexion increased with speed (P ≤ 0.002) and depth combined (P 0.001) while peak metatarsophalangeal flexion increased with WD only (P 0.001). Thoracolumbar FE-ROM between T10 and L3 and hindlimb retraction was increased by speed and WD combined (P 0.001). Hindlimb protraction was increased by speed (P 0.001) while hindlimb retraction was increased by speed and WD combined (P 0.001). Dorsoventral poll displacement was increased by speed (P 0.001) and carpal WD (P = 0.013), craniocaudal poll displacement was increased by speed and WD combined (P 0.001). Pelvic (tubera coxae and sacrum) dorsoventral displacements increased with speed and WD combined (P 0.001). Understanding the effects of speed and WD on limb, back and pelvic kinematics will improve decision making relating to dry and WT exercise within training.

Skeletal Muscle Fiber Type Composition and Citrate Synthase Activity in Fit and Unfit Warmbloods and Quarter Horses

Selective breeding and discipline specific training has led to equine breeds adept at various athletic disciplines. Breed-specific skeletal muscle adaptations have been studied in many breeds but not Warmbloods (WB). We evaluated gluteal muscle contractile muscle fiber types and citrate synthase activity (CS), a marker for mitochondrial volume density, in WB trained for dressage (second level-Grand Prix) contrasted with Quarter Horses (QH). Gluteus medius muscle biopsies from 14 unfit/18 fit dressage-trained WB and 20 unfit/16 fit reining/working cow QH were analyzed fluorometrically and fiber types determined by ATPase activity. Comparisons were made by one-way ANOVA. Unfit and fit WB had significantly higher % type 1 and lower % type 2X fibers than QH. Unfit WB had significantly higher CS than unfit QH but CS did not differ between fit WB and fit QH. CS was only significantly higher in fit versus unfit QH, not fit versus unfit WB. In conclusion, WB gluteal muscle has an inherently high % type 1/low % type 2X fibers and high mitochondrial content whether unfit or trained for dressage, contrasting QH with an inherently low % type 1/high % type 2X and low mitochondrial content, that was enhanced in fit QH. Similar CS activity in fit WB versus QH despite a two-fold difference in % type 2X fibers indicates that mitochondrial volume density cannot accurately be predicted from contractile fiber type composition.

Flexibility of equine bioenergetics and muscle plasticity in response to different types of training: An integrative approach, questioning existing paradigms

Equine bioenergetics have predominantly been studied focusing on glycogen and fatty acids. Combining omics with conventional techniques allows for an integrative approach to broadly explore and identify important biomolecules. Friesian horses were aquatrained (n = 5) or dry treadmill trained (n = 7) (8 weeks) and monitored for: evolution of muscle diameter in response to aquatraining and dry treadmill training, fiber type composition and fiber cross-sectional area of the M. pectoralis, M. vastus lateralis and M. semitendinosus and untargeted metabolomics of the M. pectoralis and M. vastus lateralis in response to dry treadmill training. Aquatraining was superior to dry treadmill training to increase muscle diameter in the hindquarters, with maximum effect after 4 weeks. After dry treadmill training, the M. pectoralis showed increased muscle diameter, more type I fibers, decreased fiber mean cross sectional area, and an upregulated oxidative metabolic profile: increased β-oxidation (key metabolites: decreased long chain fatty acids and increased long chain acylcarnitines), TCA activity (intermediates including succinyl-carnitine and 2-methylcitrate), amino acid metabolism (glutamine, aromatic amino acids, serine, urea cycle metabolites such as proline, arginine and ornithine) and xenobiotic metabolism (especially p-cresol glucuronide). The M. vastus lateralis expanded its fast twitch profile, with decreased muscle diameter, type I fibers and an upregulation of glycolytic and pentose phosphate pathway activity, and increased branched-chain and aromatic amino acid metabolism (cis-urocanate, carnosine, homocarnosine, tyrosine, tryptophan, p-cresol-glucuronide, serine, methionine, cysteine, proline and ornithine). Trained Friesians showed increased collagen and elastin turn-over. Results show that branched-chain amino acids, aromatic amino acids and microbiome-derived xenobiotics need further study in horses. They feed the TCA cycle at steps further downstream from acetyl CoA and most likely, they are oxidized in type IIA fibers, the predominant fiber type of the horse. These study results underline the importance of reviewing existing paradigms on equine bioenergetics.

Consensus for the General Use of Equine Water Treadmills for Healthy Horses

Simple Summary

Water treadmill exercise has become popular in recent years for the training and rehabilitation of equine athletes. Water treadmill exercise sessions can be tailored to the individual horse and the training/rehabilitation goals by altering the frequency, duration of exercise, water depth and belt speed. Recent work suggests that there are large variations in current modes of use between users, despite shared training or rehabilitation goals. In 2019, a group of researchers and experienced water treadmill users met in the UK to establish what was commonly considered to be best practice in the use of the modality. The result of these discussions was the production of ‘Water treadmill guidelines—a guide for users’, released in 2020 via various equestrian websites. The purpose of this article is to describe the development of these guidelines and propose them as a starting point for further collaboration between researchers and practitioners in the pursuit of ‘best practice’ in water treadmill exercise for horses.

Abstract

Water treadmill exercise has become popular in recent years for the training and rehabilitation of equine athletes. In 2019, an equine hydrotherapy working group was formed to establish what was commonly considered to be best practice in the use of the modality. This article describes the process by which general guidelines for the application of water treadmill exercise in training and rehabilitation programmes were produced by the working group. The guidelines describe the consensus reached to date on (1) the potential benefits of water treadmill exercise, (2) general good practice in water treadmill exercise, (3) introduction of horses to the exercise, (4) factors influencing selection of belt speed, water depth and duration of exercise, and (5) monitoring movement on the water treadmill. The long-term goal is to reach a consensus on the optimal use of the modality within a training or rehabilitation programme. Collaboration between clinicians, researchers and experienced users is needed to develop research programmes and further guidelines regarding the most appropriate application of the modality for specific veterinary conditions.

Conditioning equine athletes on water treadmills significantly improves peak oxygen consumption

Equine water treadmills (WT) were initially designed for rehabilitation of musculoskeletal injuries, but are also commonly used for conditioning sport horses, however the effects are not well documented. The purpose of this study was to test the effect of an 18-day WT conditioning programme on peak oxygen consumption (V̇O2peak). Nine unfit Thoroughbreds were used in a randomised controlled trial. Six horses worked daily for 18 days in stifle-height water (WT group), while 3 control horses worked without water (dry treadmill group (DT)). Preconditioning and postconditioning maximal exercise racetrack tests (800 m) were performed using a portable ergospirometry system. Measured outcomes were V̇O2, tidal volume, minute ventilation, breathing frequency, heart rate, blood lactate and instantaneous and average speed. The workload as assessed by V̇O2 was 21.7 per cent of preconditioning V̇O2peak values for WT horses. V̇O2peak on the racetrack increased by 16.1 per cent from preconditioning to postconditioning in the WT horses (P=0.03), but did not change in the DT horses. Therefore, exercising horses in high water heights may improve conditioning.

The Use of the Water Treadmill for the Rehabilitation of Musculoskeletal Injuries in the Sport Horse

In recent years, exercise on a water treadmill has come to have great relevance in rehabilitation and training centres for sport horses. Its use exploits certain physical properties of water, related to the fundamental principles of hydrodynamics, such as buoyancy, viscosity, hydrostatic pressure, and water temperature. These properties together with deliberate specification of the depth of the water and the velocity of the treadmill provide a combination of parameters that can be varied according to the purpose of the rehabilitation or training programme, the disease to rehabilitate, or the healing phase. In the current article, kinematic adaptations to exercise on a water treadmill and the direct application of such exercise to the rehabilitation of superficial and deep digital flexor tendon and accessory ligament injuries and back and joint diseases are described.

Workload of horses on a water treadmill: effect of speed and water height on oxygen consumption and cardiorespiratory parameters

Background

Despite the use of water treadmills (WT) in conditioning horses, the intensity of WT exercise has not been well documented. The workload on a WT is a function of water height and treadmill speed. Therefore, the purpose of this study was to determine the effects of these factors on workload during WT exercise.

Fifteen client-owned Quarter Horses were used in a randomized, controlled study. Three belt speeds and three water heights (mid cannon, carpus and stifle), along with the control condition (dry treadmill, all three speeds), were tested. Measured outcomes were oxygen consumption (V̇O₂), ventilation (respiratory frequency, tidal volume (V_T)), heart rate (HR), and blood lactate. An ergospirometry system was used to measure V̇O₂ and ventilation. Linear mixed effects models were used to examine the effects of presence or absence of water, water height and speed (as fixed effects) on measured outcomes.

Results

Water height and its interaction with speed had a significant effect on V̇O₂, V_T and HR, all peaking at the highest water level and speed (stifle at 1.39 m/s, median V̇O₂ = 16.70 ml/(kg.min), V_T = 6 L, HR = 69 bpm). Respiratory frequency peaked with water at the carpus at 1.39 m/s (median 49 breaths/min). For a given water height, the small increments in speed did not affect the measured outcomes. Post-exercise blood lactate concentration did not change.

Conclusions

Varying water height and speed affects the workload associated with WT exercise. The conditions utilized in this study were associated with low intensity exercise. Water height had a greater impact on exercise intensity than speed.