Contraction type influences the human ability to use the available torque capacity of skeletal muscle during explosive efforts

Abstract

The influence of contraction type on the human ability to use the torque capacity of skeletal muscle during explosive efforts has not been documented. Fourteen male participants completed explosive voluntary contractions of the knee extensors in four separate conditions: concentric (CON) and eccentric (ECC); and isometric at two knee angles (1018, ISO101 and 1558, ISO155). In each condition, torque was measured at 25 ms intervals up to 150 ms from torque onset, and then normalized to the maximum voluntary torque (MVT) specific to that joint angle and angular velocity. Explosive voluntary torque after 50 ms in each condition was also expressed as a percentage of torque generated after 50 ms during a supramaximal 300 Hz electrically evoked octet in the same condition. Explosive voluntary torque normalized to MVT was more than 60 per cent larger in CON than any other condition after the initial 25 ms. The percentage of evoked torque expressed after 50 ms of the explosive voluntary contractions was also greatest in CON (ANOVA; p , 0.001), suggesting higher concentric volitional activation. This was confirmed by greater agonist electromyography normalized to M max (recorded during the explosive voluntary contractions) in CON. These results provide novel evidence that the ability to use the muscle's torque capacity explosively is influenced by contraction type, with concentric contractions being more conducive to explosive performance due to a more effective neural strategy.

Modelling suppressed muscle activation by means of an exponential sigmoid function: Validation and bounds

“…For the pre -training datasets an α max value of 95% seems to be more suitable as the overall activation is lower, suggesting that setting the α max at 100% may be excessive. However, setting α max = 90% is likely too low to account for fast concentric contractions where the muscle activation appears to be enhanced compared to other types of contraction (Tillin et al 2012) and surpassed the values reported here (Table 2). Given this and the robustness of the fitting methods, setting α max to 100% in most cases is likely an assumption that will not introduce any meaningful errors.…”

“…This is, probably, due to the increased variability in the %VA values of some subjects obtained from eccentric contractions, mainly during the pre-training session. A number of factors may have been the cause of the observed variability such as the expectation of noxious stimuli (Shield & Zhou, 2004) or a possible variation between trials in the joint angle where the stimulus was applied (Tillin et al 2012). However, the DIFACT function appears to behave consistently irrespective of the range of %VA values or the presence of outlier points (Figure 1).…”

“…Again the function was only implicitly shown to be successful through scaling of voluntary EMG signals (Pain & Forrester, 2009). Therefore, although now used repeatedly (Lewis et al 2012;Forrester et al, 2011;Tillin et al, 2012;Pain et al, 2013) in the literature the DIFACT function has yet to be verified in an explicit way. The aims of this study were (i) to establish experimentally how well the DIFACT function follows the in vivo voluntary neural activation-angular velocity profiles in a group of subjects; and (ii) to test the robustness of the exponential DIFACT function to perturbed upper levels of maximal activation.…”

Human capacity for explosive force production: Neural and contractile determinants

“…While some preliminary research has considered the importance of quick neuromuscular activation in injury‐related situations (Lofvenberg et al., ; Konradsen et al., ; Bloem et al., ; Zebis et al., ) and athletic tasks (Pääsuke et al., ; Tillin et al., 2013a), these have typically involved relatively small groups that may not reflect the full diversity in the general population. Athletic tasks and postural corrections also involve explosive dynamic contractions that have received very little research attention, but appear to involve different activation strategies and capabilities than isometric contractions (Tillin et al., 2012b). Moreover, further research on the implications of the wide variability in explosive force production that we have documented is required.…”

Physiological and methodological aspects of rate of force development assessment in human skeletal muscle

“…Dynamic RFD has typically been assessed using different joint movements such as isolated knee extension (Dewhurst et al., ; Molina & Denadai, ), hip extension (LaRoche et al., ), squat (Sleivert & Taingahue, ), elbow flexion and extension (Mirkov et al., ; Adamson et al., ; Ingebrigtsen et al., ), bench press (Pryor et al., ; Wilson et al., ), weightlifting movements (Haff et al., ; Kilduff et al., ; Comfort, ) and different jump tests either with CMJ and DJ or without SJ stretch‐shortening cycle involvement (SSC) (Haff et al., ; Marcora & Miller, ; Kawamori et al., ; McLellan et al., ; Jakobsen et al., ). Although only few studies have compared RFD values across different contraction modes (Pryor et al., ; Wilson et al., ; Haff et al., , ; Tillin et al., ), it seems that different muscle actions (concentric, eccentric, isometric or SSC) produce large variations in RFD. In general, the results of these studies indicate that absolute RFD values are lower during isometric compared to concentric (Pryor et al., ; Wilson et al., ; Haff et al., , ) or eccentric (Pryor et al., ) test contractions, whereas the differences between absolute concentric and eccentric RFD remain less clear (Pryor et al., ).…”