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BODY SEGMENT SKELETAL MASS AS A DETERMINANT OF UPPER BODY POWER IN NORDIC SKIERS

DP Heil, FACSM

Abstract

D.P. Heil, FACSM

Montana State University – Bozeman, MT

While measures of upper body power (UBP) correlate highly with total body mass (MB) for similarly trained Nordic skiers, it is unknown whether measures of body segment masses (e.g., arms, legs, trunk) explain this relationship any better than MB alone. Previous research has speculated that MB scaling exponents for UBP could be explained by an unknown relationship between upper body segment mass and UBP. PURPOSE: This study used indirect measures of body segment skeletal mass to explain the scaling relationship between MB and UBP in trained Nordic skiers. METHODS: 23 Nordic skiers (12 men, 22±5 yrs; 11 women, 21±2 yrs), all actively training for the upcoming competitive season, had skeletal mass for individual body segments evaluated with a whole-body bioimpedance analyzer. Segment measures included muscle mass (Mm) for arms (MmLA, MmRA), legs (MmLL, MmRL), and the trunk (MmTr), whereas the MB-based outcome measures of interest included MmTr, MmArms (MmLA+MmRA), MmUB (MmArms+MmTrunk), MmLegs (MmLL+MmRL), and MmTot (MmUB+MmLegs). Maximal anaerobic UBP was determined over 20-secs (UBP20, W) with a skiing ergometer using standard testing procedures. The MB scaling exponent (b) was then determined for UBP20 (i.e., (MB)b µ UBP20) using standard log-linear regression procedures. The same exponents were then determined for the MB-based outcome measures with both MB and UBP20. To explain the value of b it was presumed a priori that MB-based outcome measures must scale with MB proportionally (i.e., (MM)b µ MB, where b = +1.0±0.05) while also scaling similarly as MB with UBP20 (±0.05) (0.05 alpha). RESULTS: Only three of the MB-based outcome measures satisfied the a priori criteria: MmTr, MmUB, and MmTot. Where the MB exponent for UBP20 was +1.46, only MmTr (+1.43), MmUB (+1.45), and MmTot (+1.49) had similar exponents (all P<0.05) while also scaling proportionally with MB (+1.05, +0.96, +0.96, respectively; P<0.05). CONCLUSIONS: The a priori criteria for explaining the scaling relationship between MB and UBP20 in trained Nordic skiers (b=+1.46) was explained by three segment measures: MmTr, MmUB, and MmTot. However, since MmTr is part of the other two outcome measures, the skeletal mass of the trunk segment (back, shoulders, chest, and core) was the single best segment mass to explain the scaling relationship between MB and UBP20.

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