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Mechanical Responses of the Human Triceps Surae after Passive "Stretching" Training of the Plantarflexors in Conditions Modulating Weightlessness

100%

Koryak Y.

Journal of Human Kinetics

2010

vol. 24

19-34

The effect of a 60-day 6° head-down tilt of bed rest with and without prolonged passive muscle "stretching" training on the mechanical properties of the human triceps surae muscle was studied in 13 healthy male subjects. One group (n = 6; mean age 30.8 ± 3.1 years) underwent a 60-day head-down tilt, and a second group (n = 7; mean age 30.4 ± 1.2 years) underwent head-down tilt with prolonged passive muscle stretching. Head-down tilt without prolonged passive muscle "stretching" training showed maximal voluntary contraction declined by 34 % (p < 0.05) and the electrically evoked tetanic tension at 150 impulses·s-1 and isometric twitch contraction reduced by 17 % (p < 0.02) and 18 % (p < 0.05), respectively. Time-to-peak tension, and half-relaxation time of the twitch slightly decreased by 3% (p > 0.05), and 7 %, respectively, but total contraction time slightly increased. The difference between electrically evoked tetanic tension and the maximal voluntary contraction expressed as a percentage of electrically evoked tetanic tension (referred to as force deficiency), has also been calculated. The force deficiency increased by 61 % (p < 0.001). After head-down tilt with prolonged passive muscle "stretching" training, the time-to-peak tension did not change, and half-relaxation time of the twitch decreased. In addition, there was a 14 % lengthening in the total duration of the twitch. The results of prolonged passive muscle "stretching" training demonstrated a clear deterioration of voluntarily and electrically induced muscle contractions. Passive "stretching" training caused a decrease by 29 % (p < 0.05) in the maximal voluntary contraction. The isometric twitch contraction, and electrically evoked tetanic tension both showed reductions by 17 %, and by 19 % (p < 0.05), respectively. The force deficiency decreased significantly by 21 % (p < 0.02). The rate of rise of electrically evoked tetanic tension and feature of voluntary contractions significantly reduced during head-down tilt with prolonged passive muscle "stretching" training. These basic experimental findings concluded that prolonged passive "stretching" training of a single muscle did not prevent a reserve of neuromuscular function.

Influence of Simulated Microgravity on Mechanical Properties in the Human Triceps Surae Muscle in vivo

75%

Koryak Y. A.

Central European Journal of Sport Sciences and Medicine

2015

vol. 11

issue 3

125-143

Purpose. The aim of the study was to investigate the effects of a simulated microgravity on the mechanical properties of the human triceps surae (TS) and to assess the effectiveness of physical training (PT) in preventing detrimental effects. Methods. Eight women (aged 26–36 years) underwent 120-d of Bed rest (BR): four underwent Bed rest only (BR group) and four performed PT during this period (BRPT group). The training sessions were conducted for 60 min each day for 6 days a week for 14 weeks, and 30–40 min twice a day for 2 weeks under the experiment conditions. PT was performed over a 4-d cycle: 3-d of training and 1-d of rest. The maximal voluntary contraction (MVC), and isometric twitch contraction (Pt), and electrically evoked tetanic tension at 150 impulses × s–1 (Ро), time-to-peak tension (TPT) of the twitch were determined. The difference between Ро and MVC expressed as a percentage of Ро and referred to a force deficiency (Рd). The MTS was determined according to the electromechanical delay (EMD) value during the explosive voluntary contraction. Surface electrodes sensed electromyographic (EMG) activity in the soleus muscle. Electromechanical delay (EMD) was the time interval between the change in EMG and movement muscle force production. Results. In the BR group, Рt, MVC, and Ро had decreased by 12, 36, 24%, respectively, but Рd had increased by 39%. TPT of the twitch had increased by 14%. The rate of increase of voluntary contractions reduced, but in the electrically evoked contraction no changes were observed. The EMD had increased by 27%. In the BREx group, МVС, Рt, and Ро decreased by 3%, and 14%, and 9%, respectively. TPT had decreased by 4%. The Pd had decreased significantly by 10%. The rate of rise increase of electrically evoked tetanic did not change significantly, but the rate of rise in isometric voluntary tension development was increased. The EMD had decreased by 12%. Conclusion. Unloading decreased function and EMD muscle and, although the PT did attenuate these effects, they did not completely prevent them. It is suggested that the total loading volume (mainly its intensity) was not sufficient to completely prevent alterations in tendon mechanical properties

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1 Central European Journal of Sport Sciences and Medicine

1 Journal of Human Kinetics

1 2015

1 2010

1 Koryak Y.

1 Koryak Y. A.

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Mechanical Responses of the Human Triceps Surae after Passive "Stretching" Training of the Plantarflexors in Conditions Modulating Weightlessness

Influence of Simulated Microgravity on Mechanical Properties in the Human Triceps Surae Muscle in vivo