Abstract
This study determined if insulin resistance (IR), induced by an acute bout of eccentrically-biased contractions that resulted in muscle injury, was attenuated following a repeated bout of contractions. Female subjects (n = 10, age 24.7 ± 3.0 yr, weight 64.9 ± 7.4 kg, height 1.67 ± 0.02 m, body fat 29.1 ± 1.9 %) performed two 30 minute bouts of downhill treadmill running (DTR 1 and DTR 2, -12 % grade, 8.0 mph) separated by 14 days. Oral glucose tolerance tests (OGTT) were administered at baseline and 48 hours following DTR 1 and DTR 2, with IR assessed by calculation of insulin and glucose areas under the curve (AUC). Maximum isometric quadriceps strength (MVC), muscle soreness (SOR), and serum creatine kinase (CK) were assessed pre-, immediately post-, and 48 hours post-DTR 1 and DTR 2 to determine the presence of muscle injury. Compared to baseline OGTT, insulin and glucose AUC (37.6 ± 8.4 and 21.4 ± 4.7 % increase, respectively), and peak insulin (44.1 ± 5.1 vs. 31.6 ± 4.0 uU·mL-1) and glucose (6.5 ± 0.4 vs. 5.5 ± 0.4 mmol·L-1) were elevated following DTR 1. These same insulin and glucose measures showed no increase above baseline 48 hours following DTR 2 (p > 0.05). MVC was reduced to a greater degree immediately following DTR 1 (16.7 ± 2.6 vs. 8.6 ± 1.2 % decline) and, although demonstrating a significant degree of recovery, remained reduced by 9.4 ± 2.7 % 48 hours following exercise. In contrast, MVC made a full recovery back to baseline values 48 hours after DTR 2. SOR was elevated to a greater degree 48 hours following DTR 1 than after DTR 2 (48.08 ± 6.16 vs. 12.70 ± 3.24 mm). There was a tendency for an attenuated serum CK response 48 hours following DTR 2 (812.8 ± 365.1 vs. 162.5 ± 42.5 U·L-1, p = 0.08). In conclusion, a novel bout of eccentrically-biased contractions resulting in a moderate degree of muscle injury confers a protective effect, whereby a subsequent bout of contractions 14 days later results in complete elimination of the IR observed following the initial bout.
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