Conventionally assessed voluntary activation does not represent relative voluntary torque production

The ability to voluntarily activate a muscle is commonly assessed by some variant of the twitch interpolation technique (ITT), which assumes that the stimulated force increment decreases linearly as voluntary force increases. In the present study, subjects (n = 7) with exceptional ability for maximal voluntary activation (VA) of the knee extensors were used to study the relationship between superimposed and voluntary torque. This includes very high contraction intensities (90–100%VA), which are difficult to consistently obtain in regular healthy subjects (VA of ∼90%). Subjects were tested at 30, 60, and 90° knee angles on two experimental days. At each angle, isometric knee extensions were performed with supramaximal superimposed nerve stimulation (triplet: three pulses at 300 Hz). Surface EMG signals were obtained from rectus femoris, vastus lateralis, and medialis muscles. Maximal VA was similar and very high across knee angles: 97 ± 2.3% (mean ± SD). At high contraction intensities, the increase in voluntary torque was far greater than would be expected based on the decrement of superimposed torque. When voluntary torque increased from 79.6 ± 6.1 to 100%MVC, superimposed torque decreased from 8.5 ± 2.6 to 2.8 ± 2.3% of resting triplet. Therefore, an increase in VA of 5.7% (from 91.5 ± 2.6 to 97 ± 2.3%) coincided with a much larger increase in voluntary torque (20.4 ± 6.1%MVC) and EMG (33.9 ± 6.6%max). Moreover, a conventionally assessed VA of 91.5 ± 2.6% represented a voluntary torque of only 79.6 ± 6.1%MVC. In conclusion, when maximal VA is calculated to be ∼90% (as in regular healthy subjects), this probably represents a considerable overestimation of the subjects’ ability to maximally drive their quadriceps muscles

Muscle fiber conduction velocity is more affected after eccentric than concentric exercise

It has been shown that mean muscle fiber conduction velocity (CV) can be acutely impaired after eccentric exercise. However, it is not known whether this applies to other exercise modes. Therefore, the purpose of this experiment was to compare the effects of eccentric and concentric exercises on CV, and amplitude and frequency content of surface electromyography (sEMG) signals up to 24 h post-exercise. Multichannel sEMG signals were recorded from biceps brachii muscle of the exercised arm during isometric maximal voluntary contraction (MVC) and electrically evoked contractions induced by motor-point stimulation before, immediately after and 2 h after maximal eccentric (ECC group, N = 12) and concentric (CON group, N = 12) elbow flexor exercises. Isometric MVC decreased in CON by 21.7 ± 12.0% (± SD, p < 0.01) and by 30.0 ± 17.7% (p < 0.001) in ECC immediately post-exercise when compared to baseline. At 2 h post-exercise, ECC showed a reduction in isometric MVC by 24.7 ± 13.7% (p < 0.01) when compared to baseline, while no significant reduction (by 8.0 ± 17.0%, ns) was observed in CON. Similarly, reduction in CV was observed only in ECC both during the isometric MVC (from baseline of 4.16 ± 0.3 to 3.43 ± 0.4 m/s, p < 0.001) and the electrically evoked contractions (from baseline of 4.33 ± 0.4 to 3.82 ± 0.3 m/s, p < 0.001). In conclusion, eccentric exercise can induce a greater and more prolonged reduction in muscle force production capability and CV than concentric exercis

balance shoes

Balance shoes raw data with unipodal/bipodal/open-eyes/closed-eyes dat

complex EMG warm-up

Complexity-based methods applied to EMG before warm-up, after a standardized warm-up and after stretching (static or neurodynamic nerve gliding)THIS DATASET IS ARCHIVED AT DANS/EASY, BUT NOT ACCESSIBLE HERE. TO VIEW A LIST OF FILES AND ACCESS THE FILES IN THIS DATASET CLICK ON THE DOI-LINK ABOV

Effect of K1 Fight on vertical jump, reaction time, and lactate production

Introduction: K1 is a combat sport with punches, kicks and knee blows. Two parameters may influence athletes\u2019 performance: injuries (e.g., Zazryn et al., 2003) and fatigue. Some studies were conducted to determine fighters physiological profile such as VO2max (Gosh et al., 1995; Guidetti et al., 2002). However, the effects of fatigue during official K1 fights remain unknown. Therefore, the aim of this study was to determine the effects of fatigue induced by an official K1 fight on vertical jump, simple visual reaction time, lactate accumulation and tactical behaviors. Methods: Eight male volunteers were recruited during regional Italian K1-style amateur competition. Mean (\ub1 SD) age, height, weight and training experience were 24.3 \ub1 1.8 yrs, 173.8 \ub1 5.6 cm, 73.3 \ub1 9.4 kg, 5.6 \ub1 2.2 yrs, respectively. Subjects performed three rounds of 90 s with 60 s rest among rounds. Tests included counter movement jumps, simple visual reaction time (both were measured with an optojump system, Microgate, Italy) and blood lactate (Lactate PRO). They were performed before warm-up and after fights. Vertical jumps and simple visual reaction times were determined 8 minutes after the end of the third round due to judge\u2019s decision and prize giving. Blood lactate was collected 2 minutes after the end of the fight. A complete match-analysis was also made using a camcorder (blow numbers). Results: Match-analysis showed 86 \ub1 23 total blows. No difference was found among rounds. However, punches (39 \ub1 16) and kicks (37 \ub1 16) number during fights was bigger (p<0.001) than knees (10 \ub1 10). While no difference among rounds was found for punches and kicks, knee blows were greater during the third round regarding with the first and second round (+4.8 \ub1 4.1, 2.8 \ub1 3.2, 2.4 \ub1 3.6, respectively, p<0.05). After the end of the fights, blood lactate was found to be on average 15.3 \ub1 1.6 mmol/L. Simple reaction times significant increased (+7.8 \ub1 5.6%; p<0.01) and no difference was found in vertical jump heights. Discussion: Our data showed an altered number of blows among rounds. The increased knee blow number may be due to either or both tactical behaviors and technical economy. High values of blood lactate suggested a key role of anaerobic metabolism in K1 fights. Although high lactate values, vertical jump heights were surprisingly unchanged, this may be due to long rest duration between the end of the fights and post-tests. After the fight, simple visual reaction tim

Effect of Kickboxing Fight on vertical jump, muscle power, and metabolic indexes

Introduction: Combat sports alternate both anaerobic and aerobic efforts (Smith, 2006). Powerful and fast anaerobic actions are of paramount importance for explosive punch or kick attacks, feigns and defensive actions. Some authors examined the effects of fight on blood lactate production among different combat sports (Khanna et al., 2006). However, especially during kickboxing fights, the effects of fatigue on muscle power and metabolic indexes remain unknown. Therefore, the aim of this research was to determine the effects of fatigue induced by a kickboxing fight on vertical jump, bench press peak power, heart rate, and blood lactate accumulation. Methods: Eleven athletes (5 females and 6 males) volunteered for the experiment. Females mean (\ub1 SD) age, height, weight and training experience were 29.6 \ub1 3.8 yrs, 164.8 \ub1 3.9 cm, 59.0 \ub1 2.4 kg, 6.4 \ub1 1.3 yrs, respectively. Males group was 26.5 \ub1 6.2 yrs, 178.3 \ub1 3.4 cm, 78.3 \ub1 10.5 kg, 8.0 \ub1 1.0 yrs, respectively. Subjects performed unofficial fights with three 120 s rounds with 60 s rest among rounds. Fights were conducted in accordance with kickboxing rules (low kick style). Athletes, referee, and coaches used their usual competition behavior. One day before fights, pre-tests were performed to determine bench press peak power using an accelerometer (Myotest, Switzerland), and vertical jump height during counter movement jumps (Optojump, Microgate, Italy). Just before fights and after warm-up, basal lactate (Lactate PRO, Japan) was collected. Heart rate (TMpro, Hosand Technologies, Italy) has been continuously recorded during fights. Finally, immediately after the end of the third round, bench press peak power, vertical jump height, and blood lactate values were evaluated for post-tests. Results: At pre-test, a sex effect was found for both bench press peak power and vertical jump height, with males demonstrating greater values than females (p<0.05). During rounds, heart rate was on average 93 \ub1 1 % of the maximal heart rate. After fights, blood lactate concentration significantly increased until 13.6 \ub1 2.3 mmol/L (p<0.001). After fights no time effect was found for both bench press peak power and counter movement jump height. Discussion: This study highlighted high heart rate and blood lactate values suggesting anaerobic metabolism plays a key role in kickboxing fights. However, aerobic power also plays an important role during recovery (e.g., lactate clearance). Neuromuscular indexes (vertical jump height and bench press peak power) were surprisingly unchanged although a fight-induced fatigue. These data could be explained by the non specific nature of these tests regarding with kickboxing skills