Key result
Endurance exercise training increased arteriolar density in the white and red portions of the gastrocnemius muscle compared to sedentary rats, while interval sprint training had no effect.
Endurance training, but not interval sprint training, increases arteriolar density in the red and white portions of the gastrocnemius muscle in rats.
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Hypothesis-generating for exercise-induced arteriolar remodeling in active muscle; human studies needed before clinical relevance.
OBJECTIVE: Exercise training has been shown to increase regional blood flow capacity to muscle tissue containing fibers that experience increased activity during exercise. The purpose of this study was to test the hypothesis that the increased blood flow capacity is partially the result of increases in arteriolar density (number of arterioles/mm2 of tissue), specifically in skeletal muscle tissue, with the largest relative increase in muscle fiber activity during training bouts. METHODS: This hypothesis was tested by comparing and contrasting the effects of endurance exercise training (ET) and interval sprint training (IST) on arteriolar density in soleus muscle (S) red (Gr) and white (Gw) portions of gastrocnemius muscle of male Sprague Dawley rats. ET rats completed 10 weeks of treadmill training 30 m/min, 15% grade, 60 min/day, 5 days/week, while IST rats completed 10 weeks of IST consisting of six 2.5-min exercise bouts, with 4.5-min rest between bouts (60 m/min, 15% incline), 5 days/week. The hypothesis would be supported if ET increased arteriolar density in S and Gr and if IST increased arteriolar density in Gw. RESULTS: ET increased arteriolar density above values of sedentary rats (SED) in both the Gw (ET = 0.93 +/- 0.19 arterioles/microm2; SED = 0.44 +/- 0.09 arterioles/microm2) and Gr (ET = 0.97 +/- 0.1 arterioles/microm2; SED = 0.51 +/- 0.06 arterioles/microm2) muscles, but not in S (ET = 1.69 +/- 0.45 arterioles/microm2; SED = 1.51 +/- 0.34 arterioles/microm2) muscle. In contrast, IST did not alter arteriolar density in Gw or Gr muscle tissue. Although arterial wall thickness was greater in S (3.95 +/- 0.40 microm) and Gr (6.24 +/- 0.59 microm) than Gw (2.76 +/- 0.18 microm), neither ET or IST altered mean wall thickness in either muscle. CONCLUSION: Increases in blood flow capacity produced in Gr and Gw by ET appear to be due in part to increased arteriolar density. In contrast, increased arteriolar density does not contribute to increased blood flow capacity of Gw in IST rats.
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Laughlin et al. (2006) studied this question. Endurance exercise training (ET) and interval sprint training (IST) vs. Sedentary rats (SED) was evaluated on Arteriolar density (number of arterioles/mm2 of tissue) in soleus and gastrocnemius muscles. Endurance exercise training increased arteriolar density in the white and red portions of the gastrocnemius muscle compared to sedentary rats, while interval sprint training had no effect.
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