Effects of Neuromuscular Fatigue on Eccentric Strength and Electromechanical Delay of the Knee Flexors: The Role of Training Status

Abstract

Purpose: To examine the effects of fatiguing isometric contractions on maximal eccentric strength and electromechanical delay (EMD) of the knee flexors in healthy young adults of different training status. Methods : Seventy-five male participants (27.7 ± 5.0 years) were enrolled in this study and allocated to three experimental groups according to their training status: athletes (ATH, n = 25), physically active adults (ACT, n = 25), and sedentary participants (SED, n = 25). The fatigue protocol comprised intermittent isometric knee flexions (6-s contraction, 4-s rest) at 60% of the maximum voluntary contraction until failure. Pre- and post-fatigue, maximal eccentric knee flexor strength and EMDs of the biceps femoris, semimembranosus, and semitendinosus muscles were assessed during maximal eccentric knee flexor actions at 60, 180, and 300°/s angular velocity. An analysis of covariance was computed with baseline (unfatigued) data included as a covariate. Results: Significant and large-sized main effects of group ( p ≤ 0.017, 0.87 ≤ d ≤ 3.69) and/or angular velocity ( p < 0.001, d = 1.81) were observed. Post hoc tests indicated that regardless of angular velocity, maximal eccentric knee flexor strength was lower and EMD was longer in SED compared with ATH and ACT ( p ≤ 0.025, 0.76 ≤ d ≤ 1.82) and in ACT compared with ATH ( p = ≤0.025, 0.76 ≤ d ≤ 1.82). Additionally, EMD at post-test was significantly longer at 300°/s compared with 60 and 180°/s ( p < 0.001, 2.95 ≤ d ≤ 4.64) and at 180°/s compared with 60°/s ( p < 0.001, d = 2.56), irrespective of training status. Conclusion: The main outcomes revealed significantly higher maximal eccentric strength and shorter eccentric EMDs of knee flexors in individuals with higher training status (i.e., athletes) following fatiguing exercises. Therefore, higher training status is associated with better neuromuscular functioning (i.e., strength, EMD) of the hamstring muscles in fatigued condition. Future longitudinal studies are needed to substantiate the clinical relevance of these findings.

Effects of Ultratrail Running on Neuromuscular Function, Muscle Damage and Hydration Status. Differences According to Training Level

“…Our study also observed how fatigue affected the amateur-level group runners to a greater extent because the reductions in the SJ ( Figure 2 A) and CMJ ( Figure 2 C) heights were significantly more marked in this group. These results fall in line with what El-Ashker et al indicated [ 61 ], who found that the subjects with a higher level of training presented better neuromuscular function with fatigue. Nonetheless, these intergroup differences were not noted for either the ABK jump ( Figure 2 E) or developed power (W) in all jumps ( Figure 2 B,D,F).…”

Maximal isokinetic elbow and knee flexor–extensor strength measures in combat sports athletes: the role of movement velocity and limb side

“…Additionally, two to three concentric and eccentric submaximal testing trials on the isokinetic device were performed during the familiarization session with upper and lower limbs of the dominant and non-dominant side at 120°/s to get accustomed to the testing protocol [ 24 , 25 ]. Before the testing and measurement trials (i.e., second session), participants performed 10 min warm-up using a cycle ergometer (Monark Exercise, Vansbro, Sweden) at a self-selected intermediate intensity workload, with a rating of perceived exertion (RPE) of 5–6 points on a 0–10 RPE scale, followed by 5 min of dynamic and static quadriceps and hamstring stretching [ 25 ]. For the upper limb muscles, 3–5 min of unloaded upper body cycling was performed using an upper-body cycle ergometer (Saratoga Cycle, Rand-Scot, CO, USA) [ 26 ].…”

Electromyographic activity in deadlift exercise and its variants. A systematic review

“…The included studies were variate in number of participants but similar in their sample population ages (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34), who had a minimum of 6 months resistance training experience. It is important to highlight the impact that training status have upon muscle activation pattern, since familiarization with the movement could substantially modify muscle activation elicited during each exercise [49][50][51]. Furthermore, twelve of the studies had a male sample, while the rest combined both genders [34-36, 41, 43], and only two studies included exclusively females [39,40].…”