RJ,
The initial proposition you put forward was that the size principle does NOT apply under eccentric loading and that eccentric loading preferentially recruited the HTMU. In support you cited a 1996 paper by Enoka.
I have tried to read some of the studies on this subject and I must say that for some of us the science is very complex and it is often difficult to understand the methodology limitations and practical application of the findings.
However what is clear is that there is NO consensus that the size principle does not apply during eccentrics.
I quote for example from a paper presented at the University of Colordao in 2004
Discharge pattern of single motor units during shortening and lengthening contractions
Benjamin Pasquet, Alain Carpentier, and Jacques Duchateau
Universite Libre de Bruxelles, Brussels, Belgium
Conflicting results have been reported regarding motor units (MUs) recruitment patterns during lengthening (LEN) contractions. Although some authors suggested that LEN contractions differ from shortening (SHO) contractions and involve a selective recruitment of high-threshold MUs (Nardone et al., 1989; see also Howel et al., 1995), others investigators showed no difference in the recruitment order (Sogaard et al. 1996; Laidlaw et al., 2000; Stotz and Bawa, 2001). In addition, there is a lack of consistent observations regarding MUs discharge rate during these two contraction types. The objective of this study was to compare the recruitment pattern and discharge rate of MUs during standardized LEN and SHO contractions.
A total of 59 MUs were investigated. No systematic recruitment of additional high-threshold MUs and derecruitment of low-threshold MUs was observed during LEN contractions. In contrast, additional MUs were occasionally recruited during SHO contractions, while the previously active units maintained their discharge rate. A different behaviour was observed in LEN contractions, since MUs with the highest recruitment threshold usually stopped to discharge before the end of the movement. During SHO contractions, the typical discharge pattern observed at the beginning of the movement was a long first interspike interval (ISI) followed by a quick increase in discharge rate. In the second part of the movement, the discharge rate was progressively enhanced. In contrast, during LEN contractions, 2-3 shorts initial ISI were followed by a more stable discharge rate throughout the movement.
In line with previous investigations (Sogaard et al. 1996; Laidlaw et al., 2000; Stotz and Bawa, 2001), our study does not support the viewpoint of a preferential recruitment of high-threshold MUs or possible change in recruitment order during LEN contractions, compared with SHO ones (Nardone et al., 1989). If some MUs recruitment or derecruitment occurred during SHO and LEN contractions, respectively, this behaviour happened in accordance with the size principle (Henneman et al., 1965). The discharge pattern, however, differed between LEN and SHO contractions. In the former condition, the lengthening of the muscle presumably have induced an increased discharge of the muscle spindles and consequently intensified muscle activation. In contrast, the unloading of the spindles at the onset of muscle shortening can explain the decrease in MUs discharge rate. The derecruitment of some MUs at the end of the LEN contraction should be due to increased passive and active force during muscle lengthening (Pasquet et al., 2000), and therefore the need of a reduced number of active MUs to maintain the same net force. It is concluded that although the discharge pattern differs in SHO and LEN contractions, in both conditions MUs are recruited and derecruited in an orderly fashion, from small to large ones and vice versa, respectively.
I do not say that the above is definitive or that you are necesasrily wrong in what you said but I have read other summaries of the literature on this topic and it is quite clear that what you have asserted as an incontrovertible scientific fact unknown to Chad and others is anything but that.
