Thus, workload may not be necessary to elicit the response of increased blood cells into the blood. Research has shown horses undergoing warm-up sessions may have increased utilization of fatty acids, thus producing less lactic acid in the subsequent work. Fatty acids are used primarily for submaximal work where the horse maintains heart rates below 150 to 160 beats per minute. With more intense work, glucose is used as the fuel source because oxygen-dependent pathways cannot produce enough energy as quickly as needed. Glucose can be broken down in the absence of oxygen, but when it is, the by-product is lactic acid.
Lactic acid is a strong acid that has been implicated with fatigue.
Low-intensity exercise increases temperature slightly. Freeman said the result may be faster contraction speed in the muscle. In humans, strenuous exercise without a warm-up period has been shown to induce abnormal heart beats. Freeman said mild stretching may benefit range of movement by increasing the elasticity of tendons and ligaments around the joints, especially in horses with past injury in a joint area. Conversely, inadequate warm-ups may increase muscle strain.