**5. Conclusion**

all testing angles (40-110o

170 Electrodiagnosis in New Frontiers of Clinical Research

increased between 40-80o

LX at longer muscle lengths.

) following training at shorter muscle lengths, MVC only significantly

in this group. Previous work from our laboratory has shown that

MVC torque did not change significantly at longer muscle lengths following a period of resistance training at shorter muscle lengths [35], and results from the current investigation show that this could be in part be mediated by a reduction in maximal activation at these lengths. Further evidence of muscle-length specificity was the fact that only LX group, who covered an entire ROM, actually demonstrated a significant relative increase in activation at each angle tested, and also that LL only showed significant relative increases in activation at longer muscle lengths (lengths where the majority of training would have taken place). In order to allow us to describe the impact of changes in activation on strength changes, we have shown that there was significantly greater muscule efficiency (EMG per unit of torque) at longer muscle lengths (i.e. in LL and LX) compared to SL, following the 8-week training program. Changes in torque generating capacity are not accounted for solely, or at times at all by increased muscle activation. Changes in muscle architecture, morphology and/ or muscle specific tension are just a few of the many other factors that can impact a muscle's ability to produce force following resistance training as well as neural adaptations (for review see [34]). However in this case, there appears to be a relationship between the increased activation of the VL muscle and the changes in torque production following resistance training in LL and

As indicated above, one of the other factors influencing changes in torque or force production following resistance exercise is muscle morphology, such as size. There is a strong positive relationship between the size of a muscle and the force it is able to exert [1]. In the current study, all of the three training groups increased the size of the VL muscle at proximal (25%), central (50%) and distal (75% of femur length) measurement sites at week 8. However in the SL group, the muscle size increment was more significant centrally rather than at proximal and distal sites of the VL, whereas both LL and LX had fairly equal distribution of size increment along the length of the muscle. Firstly, this information suggests that the resistance training program was effective in increasing muscle size, which is a well established charac‐ teristic of resistance training. Secondly, the results also suggest that the ROM involved during resistance training (i.e. the muscle lengths used) may produce region specific variations in muscle growth. Our laboratory has provided more conclusive evidence that muscle size increments at distal regions are enhanced to a greater degree immediately following resistance training at longer muscle lengths [35], however in the current study this was only apparent following two weeks of detraining, although these were still present following a total of four weeks detraining. The region specific variation in muscle size has been previously documented throughout literature (e.g. [31]), and is probably due to the unique way in which forces are transmitted along the length of a muscle when exercised at different lengths. Forces in muscles are transmitted both serially and in parallel [36], and when training at longer muscle lengths, there may be a more pronounced parallel transmission of force at distal regions of the muscle, providing a stimulus for growth in this location. In terms of muscle growth, force production and muscle stretch are potent stimulators of muscle protein synthesis, with a combination of both having an additive effect [37]. In vitro experiments have shown that when muscle cells are stretched to longer lengths, there is a marked increase in protein synthesis and growth

Performing resistance training over predominantly longer muscle lengths compared to shorter muscle lengths produces stepwise degrees of acute muscular, energetic and cardiovascular responses, which then culminate to differential magnitudes of chronic training as well as detraining adaptations. As a progression to the earlier research evidence from isometric exercise in terms of both acute [13, 14] and chronic [21] muscle length-specific training, the current study is the first to systematically show that dynamic exercise at longer muscle lengths also results in greater activation and oxygen consumption. The nature of the acute responses suggests that the muscle is more physiologically stressed at longer muscle lengths. Following a prolonged period of resistance training (i.e. an accumulation of training bouts), we show that long-length trained muscle exhibits relatively greater muscle activation, neuromuscular efficiency and hypertrophy compared with its short-length trained counterpart. Similarly with detraining, long-length training was associated with a greater retention of improvements in muscle characteristics. It is likely that in this case also, the more beneficial size increments in particular, were the result of greater physiological stress, a result of the combined effects of smaller moment arm and enhanced muscle stretch. These findings have implications for athletic, elderly, or post-operative populations to name but a few end users.
