The effect of rider weight and additional weight in Icelandic horses in tölt: part I. Physiological responses
Authors: G. Stefánsdóttir, V. Gunnarsson, Lars Roepstorff, S. Ragnarsson, A. Jansson
Journal: Animal
Summary
# Editorial Summary Researchers in Iceland investigated how rider-to-horse weight ratios between 20–35% affected physiological stress responses in eight experienced tölt horses, using an incremental exercise protocol where a single rider performed five 642-metre phases at consistent speed whilst weight was systematically added via saddle bags and a weighted vest. Heart rate, breathing frequency and blood lactate concentration all increased linearly with greater weight burden, with horses transitioning from predominantly aerobic to anaerobic work at a mean threshold of 22.7% body weight ratio—though individual variation spanned 17.0% to 27.5%, correlating significantly with back condition score rather than overall body size. Rectal temperature and blood lactate remained elevated 30 minutes post-exercise despite normalisation of heart rate and breathing, whilst all horses showed no clinical lameness or palpable back soreness in the two days following the test, suggesting the protocol itself induced no tissue damage despite metabolic strain. The findings indicate that back muscling, rather than frame size, determines an individual horse's capacity to work under load, and that many Icelandic horses commonly ridden at 30–35% bodyweight ratio are operating considerably above their aerobic threshold—with important implications for training intensity, recovery protocols and ridden workload management in this breed.
Read the full abstract on PubMed
Practical Takeaways
- •Icelandic horses can safely carry 20-22.7% of their bodyweight in rider plus tack while working primarily aerobically; exceeding ~23% substantially increases metabolic stress
- •Horse size (height, length, girth) does not reliably predict weight-carrying capacity—assess individual fitness via back condition score and monitor for signs of metabolic stress instead
- •Warm-up and cool-down recovery differ: while heart rate normalizes quickly, lactate and core temperature take longer to recover, suggesting monitoring extended recovery periods in performance work
Key Findings
- •Heart rate, breathing frequency, and lactate concentration increased linearly with rider weight ratio (20-35% of horse bodyweight)
- •Aerobic threshold (lactate 4 mmol/l) occurred at mean 22.7% weight ratio, with individual variation from 17.0-27.5%
- •Back body condition score positively correlated with aerobic threshold (r=0.75), but horse size did not predict weight tolerance
- •Heart rate and breathing frequency recovered to baseline within 30 minutes, but lactate and rectal temperature remained elevated after 30 minutes recovery