Electromyographic activity of equine abdominal muscles during single and double riding in hippotherapy.

This study examined how a horse’s abdominal muscles work during hippotherapy when there is no rider, a single rider, or two people riding together. It found that light single riding does not change abdominal muscle activity much, but double riding substantially increases and skews activation, which has implications for horse welfare and therapy planning.

Why this study matters

• Hippotherapy relies on a horse’s movement to deliver therapeutic stimuli; how the horse’s core muscles respond under different rider loads can affect both treatment quality and the animal’s welfare.
• Clinicians frequently choose between single and double riding to meet patient needs, yet the muscular impact of these configurations on the horse’s trunk has been unclear.

Study design at a glance

• Animals
  • N = 9 clinically healthy adult hippotherapy horses (mean body mass: 388 kg).
• Riders
  • Two trained female physiotherapists (50.9 and 51.3 kg) served as riders for all conditions.
  • Approximate load relative to horse mass:
    • Single rider (R1): ~13.1–13.2% of horse body mass.
    • Double riding (R2): ~26.3% combined load.
• Conditions (randomized)
  • WR: No rider.
  • R1: Single rider.
  • R2: Double riding (therapist accompanying the rider).
• Gait and speed
  • Walk at a constant 1.43 m/s.
  • Each trial: 10-second period of steady-state walking.
• Outcome measures
  • Surface electromyography (sEMG) from bilateral Rectus Abdominis (RA) and External Oblique Abdominis (EOA).
• Statistics
  • Randomized block ANOVA (blocking by horse), Tukey post hoc tests.
  • Effect sizes reported (Cohen’s d, Hedges’ g).

Key findings

• Double riding (R2) vs no rider (WR)
  • Significantly higher activation bilaterally in both RA and EOA.
  • Effect sizes large to very large (g = 1.50–2.52), indicating robust increases in muscular demand.
• Single rider (R1) vs no rider (WR)
  • No significant differences when rider load did not exceed 14.75% of horse body weight.
  • Consistent with the study’s single-rider loads (~13%), suggesting light single riding at walk minimally alters abdominal sEMG.
• Double riding (R2) vs single rider (R1)
  • Asymmetric activation emerged, notably:
    • Increased activation of the left EOA.
    • Increased activation of the right RA.
  • Patterns suggest lateralized compensations under higher, potentially off-centered loads and/or handling asymmetries.

Interpreting the muscle activity

• Functional roles
  • RA and EOA contribute to trunk stabilization, control of lumbosacral motion, and resistance to lumbar extension and lateral flexion during locomotion.
• Why double riding increases activation
  • Greater total mass requires more abdominal bracing to stabilize the trunk and pelvis at each step.
  • Two riders can introduce variable, out-of-phase movements that the horse must counter to keep balance.
• Why asymmetry appears in R2
  • Load distribution may be slightly off-center depending on seating and posture of both riders.
  • Ground handling often occurs from the horse’s left side; rein and handler influences can bias trunk muscle use.
  • Individual horse lateralization (natural sidedness) may interact with added load to produce side-dominant activation.
  • These are plausible mechanisms consistent with the observed left EOA and right RA predominance, but direct causation was not tested.

Practical implications for hippotherapy

• Choosing riding configuration
  • When therapeutic goals permit, prefer single riding with light riders (≤ ~14–15% body mass) at walk to minimize trunk muscle perturbation.
  • Reserve double riding for cases where it is clinically necessary (e.g., safety, facilitation), acknowledging higher muscular demand on the horse.
• Horse selection and load management
  • Match combined rider mass to horse size; larger, well-conditioned horses better tolerate double-rider loads.
  • Consider that the study’s double riding approximated ~26% of body mass; this level substantially increased abdominal workload.
  • If double riding is required, reduce session duration, include frequent rest, and rotate horses to limit cumulative strain.
• Reducing asymmetry during double riding
  • Strive for centered seating of both riders and minimize sustained leaning or rotation.
  • Alternate handling sides when safe, or incorporate symmetrical leading strategies to avoid consistent left-sided bias.
  • Use appropriately fitted pads/tack to improve load distribution and rider stability.
• Conditioning and monitoring
  • Incorporate core-strengthening and straightness work for therapy horses outside of sessions.
  • Monitor for early signs of fatigue or asymmetry (e.g., changes in stride regularity, reluctance to bend to one side, back sensitivity) and adjust workload accordingly.

Welfare considerations

• Load magnitude matters
  • Common equestrian guidance often cites keeping rider load around or below ~20% of horse body mass; exceeding this may increase physiologic and musculoskeletal strain, especially with additional asymmetry.
  • The observed increases in abdominal sEMG with ~26% load signal greater stabilizing effort and potential for fatigue if sustained.
• Operational safeguards
  • Limit double-riding duration at walk, and avoid prolonged sessions without breaks.
  • Schedule recovery days for horses frequently used in double riding.
  • Regularly reassess saddle/pad fit and rider positioning practices to mitigate uneven forces.

Strengths and limitations

• Strengths
  • Within-horse randomized comparisons across three standardized conditions at a controlled speed.
  • Bilateral sEMG sampling of key abdominal stabilizers.
  • Use of randomized block ANOVA with post hoc testing and effect sizes for interpretability.
• Limitations
  • Small sample (n = 9) and brief 10-second epochs may limit generalizability and sensitivity to longer-term fatigue.
  • Only walk gait and specific rider body masses were examined; results may differ at other gaits, with heavier riders, or different rider configurations.
  • Surface EMG on equine abdominals can be affected by motion artifact and cross-talk; exact normalization procedures are not detailed in the abstract.
  • Asymmetry mechanisms (e.g., handler side, seating specifics) were not experimentally isolated.

Future directions

• Expand to trot and varying speeds to map load–gait interactions on trunk musculature.
• Systematically vary combined rider mass and seating configuration to quantify symmetry effects.
• Integrate kinematics and ground reaction forces to link muscle activity with movement and loading.
• Assess additional musculature (e.g., longissimus dorsi, multifidus) and indicators of fatigue or discomfort over longer sessions.
• Develop practical field guidelines and decision tools for clinicians balancing therapeutic needs with equine welfare.

Bottom line

• Light single riding at walk (~13% of body mass) does not markedly change abdominal sEMG in therapy horses.
• Double riding (~26%) substantially increases abdominal muscle demand and introduces asymmetry, warranting careful management of load, duration, and positioning to protect horse welfare while delivering therapy.