Purpose: To investigate if elite endurance athletes periodized their body mass (BM) and composition from preparation (T1) to specific preparation period (T2) and if changes in BM and body composition were associated with improved endurance performance. Methods: Fifty-two elite endurance athletes participated in this study. Thirteen cross-country skiers, 7 biathletes, and 3 Nordic Combined athletes formed a group of skiers (16 men and 7 women), and 5 endurance runners, 22 orienteers, and 2 triathletes formed a group of runners (17 men and 12 women). Anthropometric (dual-energy X-ray absorptiometry) and performance (sport-specific incremental treadmill test) measurements were completed in T1 and T2. Results: No changes in BM or body composition were detected from T1 to T2 except for lean mass (LM), which increased in only runners (P = .03). Peak running speed (Vpeak; P < .001) and relative peak oxygen uptake (P = .04) increased from T1 to T2 regardless of the sport or sex. Decreased body fat mass and percentage were associated with increased Vpeak (r = -.41, P = .002; r = -.45, P < .001) and relative peak oxygen uptake (r = -.31, P = .03; r = -.32, P = .02). Changes in LM were positively associated with changes in Vpeak in female skiers (r = .80, P = .03), while almost all the female runners increased both LM and Vpeak. Conclusions: Elite endurance athletes did not systematically periodize their BM from T1 to T2. Decreases in body fat mass and percentage may be beneficial for endurance performance. Since increases in LM were associated with improved endurance performance in female athletes, body-composition manipulations should not lead to a decrease in LM.
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