Residual force enhancement (rFE) describes the increase in isometric force following muscle stretching compared to the corresponding isometric force. Even though rFE is consistently observed in isolated muscle preparations, it is not always observed in human skeletal muscle. This inconsistency might be associated with disociations between length changes in muscle tendon units (MTUs) and fibres. This prompted the question if there is rFE for conditions where the MTU is stretched while fibres shorten. Rabbit tibialis anterior (TA) MTUs (n = 4) were stretched and the isometric forces following stretching were compared to corresponding forces from isometric reference contractions. Unique combinations of stretch speed and activation were used to create conditions of continuous fibre shortening during MTU stretch.

Mean force was increased (18 ± 2%) following MTU stretching compared to the isometric reference forces. Without fibre length measurements, this result would be referred to as rFE. However, fibre shortening in the reference contractions was always greater than for the eccentric stretch contractions, suggesting that the observed increase in force might be caused by less residual force depression (rFD) in the stretch tests compared to the reference contractions. However, the work performed by fibre shortening was similar between the reference and the MTU stretch contractions, suggesting that rFD was similar for both experimental conditions. Therefore, we conclude that we observed rFE in the absence of contractile element stretching. However, a lack of knowledge of the molecular mechanisms that distinguish rFE from rFD prevents an unequivocal pronouncement of what caused the enhanced forces after active muscle stretching.

残余力增强（rFE）描述了与相应的等距力相比，肌肉拉伸后等距力的增加。即使在分离的肌肉制剂中始终观察到rFE，但并非总是在人体骨骼肌中观察到。这种不一致可能与肌腱单位（MTU）和纤维长度变化之间的分离有关。这引发了一个问题，即在MTU拉伸而纤维缩短的情况下是否存在rFE。拉伸兔胫前肌（TA）MTU（n = 4），并将拉伸后的等距力与等距参考收缩的相应力进行比较。拉伸速度和激活的独特组合被用来创造MTU拉伸过程中连续纤维缩短的条件。

与等轴测参考力相比，MTU拉伸后的平均力增加了（18±2％）。如果不进行光纤长度测量，则该结果称为rFE。但是，参考收缩中的纤维缩短始终大于偏心拉伸收缩，这表明与参考收缩相比，在拉伸测试中观察到的力增加可能是由于拉伸试验中残余力降低量（rFD）减少所致。但是，在参考和MTU拉伸收缩之间，通过纤维缩短进行的工作相似，这表明在两种实验条件下rFD都相似。因此，我们得出的结论是，在没有收缩元件拉伸的情况下观察到了rFE。然而，