Muscle Fiber Composition and Respiratory Capacity in Triathletes

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Abstract
In an effort to describe the skeletal muscle characteristics of trained triathletes, biopsies were obtained from the gastrocnemius, vastus lateralis, and posterior deltoid muscles of 11 triathletes and 4 normally active controls. Each specimen was analyzed for muscle fiber composition, respiratory capacity (QO2), and citrate synthase activity. The mean (±SE) percentage of type I fibers for the triathletes was 59 (4.0), 63 (3.3), and 60 (2.8) in the gastrocnemius, vastus lateralis, and deltoid, respectively (P>0.05). The mean (±SE) QO2 values in the gastrocnemius (4.4±0.3 ml O2 · min-1 · g-1) and the vastus lateralis (4.1±0.2) were not significantly different while the QO2 values of the deltoid (3.6±0.2) were significantly lower than the gastrocnemius (P-1 · g-1) was significantly lower than both the vastus lateralis (36.0±3.2) and the gastrocnemius (45.8±2.1) (Pr=.760) and deltoid (r=.610) (Pr=.200). No significant relationships were observed between skeletal muscle characteristics and V̇O2 max nor between skeletal muscle characteristics and performance. The results of this study demonstrate that: (1) these triathletes have a high percentage of type I fibers in all three muscle groups; (2) skeletal muscle characteristics were not highly related to laboratory or competitive performance; (3) despite a similar fiber composition, the deltoid appears to have a lower oxidative potential than the leg muscles, possibly due to the lesser use of the deltoid in normal daily activity.