Study explores how rider weight and pony age influence back muscle responses

How much weight can a horse or pony comfortably carry? It is one of the most frequently debated questions in equestrianism, with implications for both equine welfare and the sport's social licence to operate. Despite strong opinions on the subject, there is still relatively little scientific evidence to guide recommendations.

New research, recently published in the International Journal of Equine Science, sheds fresh light on the issue by examining how rider weight influences back muscle sensitivity and physiological stress in Exmoor ponies. 

The study has already attracted recognition within the equestrian community. Its findings were first presented as a scientific poster at the Horses Inside Out Conference 2026, where the work was judged the Best Scientific Poster by Professor Meriel Moore-Colyer, who led the judging of the conference's scientific research poster exhibition.  

Lead researcher, Jenna Payne, studied ten trekking Exmoor ponies with an average age of 18 years and an average bodyweight of 345 kg. Each pony completed the same 4.28 km ride on three consecutive days, carrying three different riders whose body weights represented between 9.7% and 23.1% of the pony's body weight. The riders were categorised as lightweight (LW), middleweight (MW) and heavyweight (HW).

 

Location of MNT. readings

© 2026 Payne et al (CC-BY-4.0)

To assess how the ponies responded, she measured the mechanical nociceptive thresholds (MNTs) of the epaxial muscles. These muscles run alongside the spine and play a key role in supporting both the horse's movement and the rider's weight. MNT testing uses a pressure algometer to determine how much pressure can be applied before the horse reacts. A higher threshold means more pressure is needed to provoke a response, indicating reduced sensitivity, while a lower threshold suggests increased sensitivity or tenderness.

She also measured heart rate variability (HRV), an indicator of activity within the autonomic nervous system that is commonly used to assess stress and recovery.

All ponies showed changes in back muscle sensitivity after ridden exercise. Immediately after carrying the heaviest riders, pressure thresholds increased significantly, meaning that greater pressure was required to elicit a response. This suggests that the back muscles were temporarily less sensitive to pressure immediately after exercise. No such overall effect was seen following the lightweight or middleweight rides.

Age also influenced the ponies' responses. Older ponies (18 years and above) showed increased pressure thresholds immediately after exercise regardless of rider weight. Younger ponies (17 years and under), however, only showed this response after carrying the heaviest riders.

Two hours after exercise, pressure thresholds had fallen again, indicating that muscle sensitivity had increased as the ponies recovered. In the younger ponies, thresholds after the lightweight and middleweight rides were significantly lower than they had been before exercise, suggesting that the muscles were actually more sensitive than at baseline. Older ponies did not show this pattern, pointing to possible age-related differences in short-term recovery. The authors caution, however, that the reasons for these differences remain unclear and require further investigation.

In contrast, heart rate variability changed very little throughout the study. No significant effects of rider weight or pony age were detected, apart from a small increase during the two-hour recovery period following the lightweight ride. Overall, the HRV results suggest that none of the rider weights produced sustained physiological stress in these experienced trekking ponies. 

The authors conclude that rider weight and pony age both influence short-term changes in back muscle sensitivity following ridden exercise, particularly in the mid-thoracic and lumbar regions of the back. However, the absence of marked changes in heart rate variability suggests that these local muscular responses were not accompanied by prolonged physiological stress.

The researchers emphasise that this was a preliminary study involving only ten experienced trekking ponies. They say larger studies involving different breeds, ages and fitness levels, together with longer follow-up periods, are needed before firm evidence-based recommendations can be made about appropriate rider-to-horse weight ratios.

 

For more details, see:    

Payne J, Routledge N, Charlton S, Hunnisett A.

Effects of Rider Weight and Pony Age on Epaxial Muscle Pain Sensitivity and Heart Rate Variability in Exmoor Ponies: A Preliminary Study.

Int J Equine Sci 2026;5(2):138–144.

https://rasayely-journals.com/index.php/ijes/article/view/229/161

 

See the poster

For details of Horses Inside Out Conference 2027, see: https://www.hioconference.com/