Horses experience a post-exercise inflammatory response to damaged tissues that is part of the mechanism of recovery and is indicated by heat and muscle soreness (MS). Further, old horses (OH) are at a greater risk of prolonged MS, lameness, and injury than are young horses (YH). Therefore, the objective of this study was to compare heat and MS of unconditioned young (14-16 months) and old (19-24 years) Quarter Horses after the completion of an incremental exercise test (IET: counterclockwise at 3 min at 6.44 kph, 10 min at 16.09 kph, 2 min each at 19.31 and 22.53 kph). MS evaluations were performed on neck, shoulder, back, and hip for both sides at pre, 12, 36, 60, and 84 hours post IET. FLIR images of the shoulder, forearm, back, hip, and gaskin were taken on the left side at day 0, pre-IET, 15 min, and 12, 24, 48, 72 h post-IET. Data were analyzed by repeated measures ANOVA using the MIXED procedure of SAS. There was a main effect of age on gaskin temperature, whereby YH (32.3±17.5°C) had higher temperatures than OH (31.4±17.5°C; P = 0.043). There was a tendency for an interaction of age and time for shoulders (P = 0.063) and an interaction for forearm (P = 0.03) and back (P = 0.046). At 12 h post IET, YH shoulders were higher (34.6±17.1°C) than OH (31.8±17.1°C), YH forearms were higher (34.1±17.3°C) than OH (30.4±17.1°C), and YH backs (33.4±17.3°C) were higher than OH (32±17.3°C). Necks were sorer on the right side 36 h post-IET compared to pre-exercise (P = 0.033) and 60 hours compared to 12 hours post IET (P = 0.033). Muscle soreness increased in the right hip from pre-IET to 36 h post-IET (P = 0.037). No other differences were observed. Our results suggest that YH have higher surface temperatures than OH but this was not associated with MS.