Sex-specific Differences In Biomechanical Strategies During A Single-leg Countermovement Jump

Abstract

and finish phases of the stroke. PURPOSE: To compare joint angles and peak angular velocities of the knee and lumbar spine during the feet-out drill, as well as peak lumbar extension timing within the stroke, on a static (SRE) versus dynamic (DRE) rowing ergometer, as well as between sexes. METHODS: 15 experienced rowers (8 females, 22.73 ± 5.51 years) participated in this study. Using a within-subjects, repeated measures design, subjects completed 750 meters of the feet-out drill on both the SRE and DRE at 20 ± 1 strokes per minute. Seven inertial measurement units were placed on the subjects' 7th cervical spinal process, sacrum, 12th thoracic spinal process, and bilateral thigh and leg segments. Peak lumbar extension timing for ten consecutive strokes was identified as a percentage of stroke. The beginning and end of each stroke was defined by maximum knee flexion. A mixed between-within ANOVA was run to compare males and females and between ergometers. Paired t-tests were run for kinematic variables between ergometers. Pearson correlations were used for weight and height with kinematic data. RESULTS: Peak lumbar extension occurred later on the SRE (38.08 ± 5.18%) when compared to the DRE (34.60 ± 3.93%, p = .01). Likewise, females had an earlier peak lumbar extension (n = 7, DRE 32.43 ± 3.05%, SRE 35.23 ± 4.12%) compared to males (n = 6, DRE 37.13 ± 3.40%, SRE 41.40 ± 4.41%, p =.01). SRE lumbar ROM and weight had a strong correlation (r = .86, p < .01) which was not seen with the DRE. CONCLUSIONS:The ratio of the phases of the drive and finish of the rowing stroke appears to be affected during the feet-out drill on a SRE vs DRE. The DRE appears to be the more ideal choice for a stroke with less emphasis on the second half of the drive and finish phases and for limiting lumbar spine ROM in heavier athletes. Coaches and athletes should proceed with awareness of such differences when choosing to complete the drill on a dynamic or static rowing ergometer.