不同表現參數計算離心利用率以評估牽張──收縮循環效益之差異

Differences in eccentric utilization ratios calculated using various performance parameters in assessing the benefits of stretch-shortening cycles

緒論：過去研究時常使用離心利用率來評估反向跳的牽張-收縮循環效益(stretch-shortening cycle, SSC)，但以不同表現參數所計算的離心利用率(eccentric utilization ratio, EUR)會有所差異，因此，有必要進一步釐清這些差異與SSC動作之下肢動態肌力特徵的關聯性。目的：以跳躍高度(jump height, JH)、推蹬力峰值(peak force, PF)以及向心功率峰值(peak power, PP)等不同參數計算離心利用率指標(EUR-JH、EUR-PF、EURPP)，並比較各EUR指標高、低之間下肢動態肌力參數的差異，以了解不同EUR可能反映出的肌力特徵為何。方法：本研究招募30位大專體育系男性學生，進行蹲踞跳與反向跳測試，以測力板進行資料的收集後，分別計算EUR-JH、EUR-PF、EUR-PP，並以中位數法將受試者區分為高、低離心利用率組。以獨立樣本t-test分別考驗三種評估指標下，兩組間各下肢動態肌力參數是否有差異存在。結果：以EUR-JH區分之高、低離心利用率組，在各項動態肌力特徵皆未達顯著差異(p > .05)；以EUR-PF區分時，高離心利用率組有較短的制動期時間、推蹬期時間(p < .05)，以及較大的制動發力率、推蹬發力率、下肢勁度(p < .05)；以EUR-PP區分時，高離心利用率組有較短的制動期時間與攤還期時間(p < .05)，以及較大的制動末點力、制動發力率、離心功率峰值、推蹬發力率以及下肢勁度(p < .05)。結論：EUR-PF、EUR-PP較高者在制動(牽張)以及推蹬(收縮)時皆有較佳的跳躍動作時間與張力表現，可用於鑑別SSC的效益，尤其EUR-PP可反映更多的相關指標的差異(如攤還期、制動末點力、離心功率)。然而，EUR-JH高、低者之間在各項下肢動態肌力參數皆無顯著差異，故可能較不適合用於評估SSC的效益。

Introduction: Previous studies have typically used the eccentric utilization ratio (EUR) to evaluate the benefits of stretch-shortening cycles (SSC) in countermovement jumps (CMJ). However, EURs calculated using different performance parameters may vary. Therefore, further clarifying these differences and their relationship to the dynamic muscular strength characteristics of the lower limbs during SSC actions is imperative. Purpose: To compare the differences in various dynamic muscle strength parameters of the lower limbs between high and low EURs calculated using jump height (EUR-JH), peak force (EUR-PF), and peak power (EUR-PP). This study aimed to understand what strength characteristics might be reflected by different EURs. Methods: Thirty male students were recruited from a college physical education department to participate in CMJ and squat jump tests. Data were collected using a force plate, and the EUR-JH, EUR-PF, and EUR-PP were calculated. The participants were divided into high and low EUR groups based on the medians. Independent samples t-tests were used to examine differences in various lower limb dynamic muscle strength parameters between the high and low groups for each EUR. Results: For EUR-JH, dynamic muscle strength characteristics did not differ significantly between the high and low groups (p > 0.05). For EUR-PF, the high group had significantly shorter braking phase times and shorter propulsive phase times (p < 0.05) and higher rates of braking force development, rates of propulsive force development, and leg stiffness (p < 0.05). For EUR-PP, the high group had significantly shorter braking phase times and amortization phase times (p < 0.05) and higher braking end forces, rates of braking force development, peak eccentric power, rates of propulsive force development, and leg stiffness (p < 0.05). Conclusion: Individuals with higher EUR-PF and EUR-PP demonstrated superior temporal and tension performance during both the braking (eccentric) and propulsion (concentric) phases, suggesting that these metrics can be employed to differentiate the benefits of SSC. Notably, the EUR-PP can reflect more variations in related indicators such as amortization phase time, braking end force, and eccentric power. Conversely, the lack of significant differences in various lower limb dynamic muscle strength parameters between individuals with high and low EUR-JH suggests that EUR-JH may be less appropriate for assessing the benefits of SSC.