Effects of fatigue and sprint training on electromechanical delay of knee extensor muscles

Abstract

Electromechanical delay (EMD) of knee extensors in isometric contraction was investigated in six healthy men before and after four periods of 30-s allout sprint cycling exercise, conducted pre and post a 7-week sprint cycling training programme. The EMD was lengthened from 40.4 (SEM 3.46) ms at rest to 63.4 (SEM 7.80) ms after the fatiguing exercise (P < or = 0.05) in the pre-training test. During maximal voluntary contractions (MVC) conducted after the fatiguing exercise, the peak contraction force (Fpeak) and peak rate of force development (RFDpeak) were reduced by 51%-56% and 38%-50%, respectively (both P < or = 0.05). The mechanisms of EMD lengthening during fatigue could have been due to the deterioration in muscle conductive, contractile or elastic properties and require further study. The training programme increased the total work performed during the four periods of sprint exercise (P < or = 0.05). However, no significant training effects were found in the resting or postexercise EMD, Fpeak and RFDpeak during isometric MVC. These unchanged isometric contraction variables but enhanced dynamic performance suggest that isometric tests of muscle are insensitive to the neuromuscular adaptations to sprint training.

Effects of acute fatigue on the volitional and magnetically-evoked electromechanical delay of the knee flexors in males and females

“…These findings, together with corroborating findings from other studies (e.g. Gleeson et al 2000;Gleeson et al 1998b;Zhou et al 1996) may suggest a reduced capability of the dynamic stabilisers to provide forceful corrective responses to mechanical loading of the knee. Such fatigue-related changes in neuromuscular performance may be interpreted to represent an increased risk of injury (Chan et al 2001;Gleeson et al 1998b;Mercer et al 1998), which may be amplified particularly at knee angles where key ligamentous structures are already under greatest mechanical strain (Beynnon and Johnson 1996).…”

Predictor-Based Compensation for Electromechanical Delay During Neuromuscular Electrical Stimulation

“…[21] and [55] and references therein). The fact that the control gain was chosen without the knowledge of the ratio (the ratio contains unknown muscle force-length and muscle force-velocity relationships, and moment arm; see Section II) shows that the gain condition in Remark 1 is sufficient but not necessary.…”

“…The EMD was measured as the difference between the time when voltage is applied at the electrode sites on the skin and the time when the angle encoder detects the first leg movement. Although in [21], [22], and [55] the EMD is measured as the time lag between the onset of muscle electrical activity (electromyogram, EMG) and tension development in human muscle, the method employed in this study is practical for use during NMES since firstly, significant (and sometimes questioned) filtering efforts are required to reliably measure EMG signal during NMES; secondly, the employed method accounts for total time course taken by the applied voltage at the electrode-skin interface to the observation of leg movement (analogous to muscle force production).…”

Repeated exercise stress impairs volitional but not magnetically evoked electromechanical delay of the knee flexors

“…Whilst there is a body of research that explores the electromechanical responses of the knee extensors subsequent to fatiguing exercise (e.g. Chan et al, 2001;Zhou et al, 1998), indicating up to a 70% fatiguerelated lengthening of EMD in males (Zhou, McKenna, Lawson, Morrison, Fairweather, 1996), there is limited research into the EMD of the knee flexor musculature following exercise, especially in females. The efficacy of dynamic joint stabilisation during sudden loading is dependent on the temporal parameters related to the initiation and development of muscle force, including EMD and the magnitude of the force response (Blackburn et al, 2008;Linford et al, 2006).…”