Estimated Muscle Fiber Type and Blood Lactate Responses in NCAA Division III Sprint and Distance Swimmers: An Exploratory Feasibility Study

Background and Objectives: Swimming has sprint and distance events, with current performance often driving selection rather than physiological characteristics of the athlete (e.g., muscle fiber type, blood lactate, etc.), especially among NCAA Division III swimmers, where these characteristics are unknown. We aimed to characterize the differences in estimated muscle fiber types (% fast twitch, %FT) and blood lactate (Blac) response to the maximal anaerobic lactate swim test (MANLT) between collegiate distance and sprint collegiate swimmers. Methods: Twenty-two college-aged (19.7 ± 1.0 yr) DIII swimmers (n = 13 sprint, n = 9 distance) performed an isokinetic muscular fatigue protocol to estimate their %FT, as well as their maximal and minimum Blac values and clearance rate (Blac recovery) (3 and 12 min post) after the MANLT was performed on two separate days (>48 h between). Results: There were no significant differences between sprint swimmers and distance swimmers in maximal Blac levels (11.6 ± 2.5 vs. 10.5 ± 3.4 mM, p = 0.38, d = 0.3), minimal Blac levels (9.3 ± 2.9 vs. 8.3 ± 3.3 mM, p = 0.45, d = 0.3), and percent decreases from 0 to 3 min (0.9 ± 13.1 vs. 9.9 ± 9.5, p = 0.09, d = 0.7), 0–12 min (15.4 ± 15.6 vs. 19.7 ± %, p = 0.52, d = 0.2), and 3–12 min (14.7 ± 12.5 vs. 11.04 ± 11.2%, p = 0.48, d = 0.3) Blac recovery. No significant differences were identified in estimated %FT between sprinters and distance swimmers (52 ± 6.4 vs. 45 ± 10.51, p = 0.056). Both extensor and flexor %FT estimations showed 69.2% and 66.7% accuracy in matching coach-identified event, with their respective estimated fiber type. A positive relation was identified between %FT knee flexor fibers and Blac (r = 0.44) and between %FT knee extensor fibers and Blac (r = 0.48) for all swimmers. Conclusions: This preliminary study suggests that athlete specialization is generally accurate to the physiology of the swimmer, namely anaerobic capacity and estimated fiber type.