Rousanoglou Elissavet N, Oskouei Ali E, Herzog Walter
Faculty of Physical Education & Sport Science, National & Kapodistrian University of Athens, Ethnikis Antistasis 41, Daphne, 172-37, Greece.
J Biomech. 2007;40(1):1-8. doi: 10.1016/j.jbiomech.2005.12.002. Epub 2006 Jan 27.
Mechanical properties of skeletal muscles are often studied for controlled, electrically induced, maximal, or supra-maximal contractions. However, many mechanical properties, such as the force-length relationship and force enhancement following active muscle stretching, are quite different for maximal and sub-maximal, or electrically induced and voluntary contractions. Force depression, the loss of force observed following active muscle shortening, has been observed and is well documented for electrically induced and maximal voluntary contractions. Since sub-maximal voluntary contractions are arguably the most important for everyday movement analysis and for biomechanical models of skeletal muscle function, it is important to study force depression properties under these conditions. Therefore, the purpose of this study was to examine force depression following sub-maximal, voluntary contractions. Sets of isometric reference and isometric-shortening-isometric test contractions at 30% of maximal voluntary effort were performed with the adductor pollicis muscle. All reference and test contractions were executed by controlling force or activation using a feedback system. Test contractions included adductor pollicis shortening over 10 degrees, 20 degrees, and 30 degrees of thumb adduction. Force depression was assessed by comparing the steady-state isometric forces (activation control) or average electromyograms (EMGs) (force control) following active muscle shortening with those obtained in the corresponding isometric reference contractions. Force was decreased by 20% and average EMG was increased by 18% in the shortening test contractions compared to the isometric reference contractions. Furthermore, force depression was increased with increasing shortening amplitudes, and the relative magnitudes of force depression were similar to those found in electrically stimulated and maximal contractions. We conclude from these results that force depression occurs in sub-maximal voluntary contractions, and that force depression may play a role in the mechanics of everyday movements, and therefore may have to be considered in biomechanical models of human movement.
骨骼肌的力学特性通常是针对受控的、电诱导的、最大或超最大收缩进行研究的。然而，许多力学特性，如力-长度关系以及主动肌肉拉伸后的力增强，在最大和次最大收缩，或电诱导和自主收缩情况下有很大不同。力衰减，即在主动肌肉缩短后观察到的力的损失，已在电诱导和最大自主收缩中被观察到并得到充分记录。由于次最大自主收缩对于日常运动分析和骨骼肌功能的生物力学模型来说可能是最重要的，因此研究这些条件下的力衰减特性很重要。所以，本研究的目的是检查次最大自主收缩后的力衰减情况。使用拇内收肌进行了最大自主用力30%时的等长参考收缩和等长-缩短-等长测试收缩组。所有参考收缩和测试收缩均通过反馈系统控制力或激活来执行。测试收缩包括拇内收肌在拇指内收10度、20度和30度时的缩短。通过比较主动肌肉缩短后的稳态等长力（激活控制）或平均肌电图（EMG）（力控制）与相应等长参考收缩中获得的力和平均肌电图，来评估力衰减。与等长参考收缩相比，缩短测试收缩中的力降低了20%，平均EMG增加了18%。此外，力衰减随着缩短幅度的增加而增加，力衰减的相对大小与电刺激和最大收缩中发现的相似。从这些结果我们得出结论，力衰减发生在次最大自主收缩中，并且力衰减可能在日常运动力学中起作用，因此在人体运动的生物力学模型中可能必须予以考虑。
