Kinematic Analysis During Straight Line Free Swimming in Horses: Part 1 - Forelimbs

Therapeutic Exercises for Rehabilitation of Muscle Injury

Successful rehabilitation of muscle injury requires a comprehensive understanding of the injury process, healing phases, and resources to be employed. The initial phase is characterized by acute inflammatory signs, followed by the regenerative and remodeling phases. Therapeutic exercises can be utilized in all 3 phases, progressing from isometric exercises to aquatic therapies. The classification and phase of injury and the individual response to the applied therapies will guide the progression of the therapeutic exercises through the rehabilitation program.

Description and Analysis of Horse Swimming Strategies in a U-Shaped Pool

Aquatic training has been integrated into equine rehabilitation and training programs for several decades. While the cardiovascular effects of this training have been explored in previous studies, limited research exists on the locomotor patterns exhibited during the swimming cycle. This study aimed to analyze three distinct swimming strategies, identified by veterinarians, based on the propulsion phases of each limb: (S1) two-beat cycle with lateral overlap, (S2) two-beat cycle with diagonal overlap, and (S3) four-beat cycle. 125 underwater videos from eleven horses accustomed to swimming were examined to quantify the differences in locomotor patterns between these strategies. Initially, a classifier was developed to categorize 125 video segments into four groups (CatA to CatD). The results demonstrated that these categories correspond to specific swimming strategies, with CatA aligning with S1, CatB with S2, and CatC and CatD representing variations of S3. This classification highlights that two key parameters, lateral and diagonal ratios, are indeed effective in distinguishing between the different swimming strategies. Additionally, coordination patterns were analyzed in relation to these swimming strategies. One of the primary findings is the variability in swimming strategies both within and between individual horses. While five horses consistently maintained the same strategy throughout their swimming sessions, six others exhibited variations in their strategy between laps. This suggests that factors such as swimming direction, pauses between laps, and fatigue may influence the selection of swimming strategy. This study offers new insights into the locomotor patterns of horses during aquatic training and has implications for enhancing the design of rehabilitation protocols.

Development of a Methodology for Low-Cost 3D Underwater Motion Capture: Application to the Biomechanics of Horse Swimming

Hydrotherapy has been utilized in horse rehabilitation programs for over four decades. However, a comprehensive description of the swimming cycle of horses is still lacking. One of the challenges in studying this motion is 3D underwater motion capture, which holds potential not only for understanding equine locomotion but also for enhancing human swimming performance. In this study, a marker-based system that combines underwater cameras and markers drawn on horses is developed. This system enables the reconstruction of the 3D motion of the front and hind limbs of six horses throughout an entire swimming cycle, with a total of twelve recordings. The procedures for pre- and post-processing the videos are described in detail, along with an assessment of the estimated error. This study estimates the reconstruction error on a checkerboard and computes an estimated error of less than 10 mm for segments of tens of centimeters and less than 1 degree for angles of tens of degrees. This study computes the 3D joint angles of the front limbs (shoulder, elbow, carpus, and front fetlock) and hind limbs (hip, stifle, tarsus, and hind fetlock) during a complete swimming cycle for the six horses. The ranges of motion observed are as follows: shoulder: 17 ± 3°; elbow: 76 ± 11°; carpus: 99 ± 10°; front fetlock: 68 ± 12°; hip: 39 ± 3°; stifle: 68 ± 7°; tarsus: 99 ± 6°; hind fetlock: 94 ± 8°. By comparing the joint angles during a swimming cycle to those observed during classical gaits, this study reveals a greater range of motion (ROM) for most joints during swimming, except for the front and hind fetlocks. This larger ROM is usually achieved through a larger maximal flexion angle (smaller minimal angle of the joints). Finally, the versatility of the system allows us to imagine applications outside the scope of horses, including other large animals and even humans.

Free Swimming and Exercise-Induced Pulmonary Hemorrhage in Endurance Horses: A Preliminary Study

Swimming is used for rehabilitation of musculoskeletal injuries and for conditioning to improve equine fitness. However, there are anecdotal reports that suggest that tethered swimming can induce epistaxis, likely secondary to exercise-induced pulmonary hemorrhage (EIPH). The objective of this observational, prospective study was to investigate if EIPH occurs during intensive free-swimming training sessions (5 × 70m) using 15 endurance horses. On tracheo-bronchoscopic evaluations following swimming, low grade mucus scores were observed, but no tracheal blood was observed. Bronchoalveolar lavage fluid analysis revealed a low cellularity, and the median red blood cell count (RBCs) was 271 cells/μL (interquartile range 150-363 cells/μL), which is much lower than the threshold of RBCs >1,000 cells/μL for horses to be considered positive for EIPH. Therefore, free swimming does not seem to predispose endurance horses to EIPH following a typical free-swimming training session.

Kinematic Analysis During Straight Line Free Swimming in Horses: Part 2 - Hindlimbs

Background

Swimming is used for rehabilitation and conditioning purposes in equine sports medicine. We described the swimming kinematics of the equine forelimbs in Part 1. The aim of Part 2 is to assess stifle, tarsus, and hind fetlock joints kinematics in swimming horses. The objectives were 1- to calculate and compare joint angles during swimming against passive mobilizations (PM), 2- to determine joints angular velocities during a swimming stride cycle.

Methods

Eleven elite endurance horses were used to swim in a 100-meter straight pool. Underwater (swimming) and overground PM videos were recorded from the horses' left side. Joint markers were applied on the lateral hoof wall, lateral metatarsal epicondyle, lateral aspect of the talus, lateral femoral epicondyle, and great trochanter of the femur. As a reference, maximal fetlock, tarsus, and stifle flexion/extension angles were determined during PM overground. Differences between angle extrema, angular velocities, and range of motion (ROM) were statistically compared.

Results

The tarsus ROM was similar during PM and swimming. The stifle and fetlock ROM were greater during PM, although the stifle flexion was greater during swimming. The stifle and tarsus had the greatest hindlimb angular velocity during the swimming cycle. Greater angular velocities were observed during the retraction phase for all the hindlimb joints.

Conclusion

A short retraction phase with great angular velocity for the joints of interest characterized the swimming pattern observed. Swimming may be beneficial in horses when an increased ROM of the tarsus and stifle or a reduced fetlock extension is indicated for rehabilitation purposes.