Seven subjects (1 woman) performed an incremental isotonic test on a Kin-Com isokinetic apparatus to determine their maximal oxygen consumption during bilateral knee extensions (Vo(2 sp)). A multisensor thermal probe was inserted into the left vastus medialis (middiaphysis) under ultrasound guidance. The deepest sensor (tip) was located approximately 10 mm from the femur and deep femoral artery (T(mu 10)), with additional sensors located 15 (T(mu 25)) and 30 mm (T(mu 40)) from the tip. Esophageal temperature (T(es)) was measured as an index of core temperature. Subjects rested in an upright seated position for 60 min in an ambient condition of 22 degrees C. They then performed 15 min of isolated bilateral knee extensions (60% of Vo(2 sp)) on a Kin-Com, followed by 60 min of recovery. Resting T(es) was 36.80 degrees C, whereas T(mu 10), T(mu 25), and T(mu 40) were 36.14, 35.86, and 35.01 degrees C, respectively. Exercise resulted in a T(es) increase of 0.55 degrees C above preexercise resting, whereas muscle temperature of the exercising leg increased by 2.00, 2.37, and 3.20 degrees C for T(mu 10), T(mu 25), and T(mu 40), respectively. Postexercise T(es) showed a rapid decrease followed by a prolonged sustained elevation approximately 0.3 degrees C above resting. Muscle temperature decreased gradually over the course of recovery, with values remaining significantly elevated by 0.92, 1.05, and 1.77 degrees C for T(mu 10), T(mu 25), and T(mu 40), respectively, at end of recovery (P < 0.05). These results suggest that the transfer of residual heat from previously active musculature may contribute to the sustained elevation in postexercise T(es).

We examined the effect of two levels of exercise-induced hypotension on esophageal (Tes) and active and nonactive muscle temperatures during and following exercise. Seven males performed an incremental isotonic test on a Kin-Com isokinetic apparatus to determine their peak oxygen consumption during bilateral knee extensions (VO2sp). This was followed on separate days by 15-min of isolated bilateral knee extensions at moderate (60% VO2sp) (MEI) and high (80% VO2sp) (HEI) exercise intensities, followed by 90 min of recovery. Muscle temperature was measured with an intramuscular probe inserted in the left vastus medialis (Tvm) and triceps brachii (Ttb) muscles under ultrasound guidance. The deepest sensor (tip) was located approximately 10 mm from the femur and deep femoral artery and from the superior ulnar collateral artery and humerus for the Tvm and Ttb, respectively. Additional sensors were located 15 and 30 mm from the tip with an additional sensor located at 45 mm for the Tvm measurements only. Following exercise, mean arterial pressure (MAP) remained significantly below preexercise rest for the initial 60 min of recovery after MEI and for the duration of the postexercise recovery period after HEI (P< or =0.05). After HEI, significantly greater elevations from preexercise rest were recorded for Tes and all muscle temperatures paralleled a greater decrease in MAP compared with MEI (P< or =0.05). By the end of 90-min postexercise recovery, MAP, Tes, and all muscle temperatures remained significantly greater after HEI than MEI. Furthermore, a significantly shallower muscle temperature profile across Tvm, relative to preexercise rest, was observed at the end of exercise for both HEI and MEI (P< or=0.05), and for 30 min of recovery for MEI and throughout 90 min of recovery for HEI. No significant differences in muscle temperature profile were observed for Ttb. Thus we conclude that the increase in the postexercise hypotensive response, induced by exercise of increasing intensity, was paralleled by an increase in the magnitude and recovery time of the postexercise esophageal and active muscle temperatures.

This study was designed to evaluate the role of non-active tissue in the retention and dissipation of heat during and following intense isolated muscle activity. Six subjects performed an incremental isotonic test (constant angular velocity, increases in force output) on a KIN-COM isokinetic apparatus to determine their maximal oxygen consumption during single knee extensions (VO2sp). In a subsequent session, a thin wire multi-sensor temperature probe was inserted into the left vastus medialis under ultrasound guidance at a specific internal marker. The deepest temperature sensor (tip, Tmu10) was located approximately 10 mm from the femur and deep femoral artery with 2 additional sensors located at 15 (Tmu25) and 30 (Tmu40) mm from the tip. Implant site was midway between and medial to a line joining the anterior superior iliac spine and base of patella. Esophageal temperature (Tes) temperature was measured as an index of core temperature. Subjects rested in a supine position for 60 min followed by 30 min of seated rest in an ambient condition of 22 degree C. Subjects then performed 15 min of isolated single right knee extensions against a dynamic resistance on a KIN COM corresponding to 60% of VO2sp at 60 degree x sec(-1). Exercise was followed by 60 min of seated rest. Resting Tes was 37 degree C while Tmu10, Tmu25, and Tmu40 were 36.58, 36.55 and 36.45 degree C, respectively. Exercise resulted in a Tes increase of 0.31 C above pre-exercise resting. Tmu of the non-exercising leg increased 0.23, 0.19 and 0.09 degree C for Tmu10, Tmu25, and Tmu40, respectively. While Tes decreased to baseline values within approximately 15 min of end-exercise, Tmu10 reached resting values following approximately 40 min of recovery. These results suggest that during isolated muscle activity, convective heat transfer by the blood to non-active muscle tissue may have a significant role in maintaining resting core temperature.

A technique for implanting multi sensor temperature probes in muscle tissue was developed to optimize the accuracy of the tissue temperature measurements and the internal localization of the probe. Real time ultra-sound imaging was used to (a) determine the best perpendicular insertion tract, (b) guide the insertion of the probe in order to avoid major blood vessels, and (c) verify the insertion point relative to discernable anatomic reference structures such as arteries and bone.

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