Studies into horse-saddle-rider interaction demonstrate that increased vertical forces on the horse’s back are potentially damaging to the musculoskeletal system, and any practice that could lead to this warrants investigation. The contribution of the stirrups in stabilising the bodyweight of the rider, and the effect of riding without stirrups on force distribution to the horse, has yet to be fully described in the literature. The current study therefore aimed to compare saddle and stirrup forces in three conditions; sitting trot, rising trot, and sitting trot without stirrups on the riding simulator. Fourteen amateur female riders of mean age 34.6 ±10 years participated in the study and 20 seconds of data were collected for saddle and stirrup force across the three conditions. Mean and peak forces were extracted from the data for total force under the whole saddle, left and right sides of the saddle separately, left and right stirrups, and both stirrups combined. Peak vertical saddle forces were significantly higher in sitting trot without stirrups than with (P=0.011). Higher mean and peak saddle forces were seen on the right hand side in all conditions (P<0.001) and there was an overall tendency for higher left stirrup forces in both sitting and rising trot with this being significant for peak force in sitting trot (P=0.039). The higher forces recorded when trotting without stirrups indicate that the stirrups play an important role in controlling the vertical acceleration of the rider in relation to the horse, however further studies are needed on live horses before any specific recommendations can be made regarding training practices. Asymmetrical saddle forces have a potentially negative effect on the horse and future research should also aim to identify the underlying causes of these patterns of rider asymmetry to improve both horse welfare and performance.