Łochyński Dawid, Kaczmarek Dominik, Grześkowiak Marcin, Majerczak Joanna, Podgórski Tomasz, Celichowski Jan
Department of Neuromuscular Physiotherapy, Poznan University of Physical Education, Poznań, Poland.
Department of Physiology and Biochemistry, Poznan University of Physical Education, Poznań, Poland.
Front Physiol. 2021 May 14;12:652299. doi: 10.3389/fphys.2021.652299. eCollection 2021.
Post-tetanic potentiation (PTP) of force depends on intramuscular Ca levels and sensitivity and may be affected by fatigue. The aim of this study was to determine the ability of isolated fast fatigue-resistant (FR) and fast-fatigable (FF) motor units (MUs) to potentiate force evoked with single and 40-Hz electrical stimulation after 5 weeks of voluntary weight-lifting training. Tetanic contractions evoked by gradually increasing (10-150 Hz) stimulation frequency served as conditioning stimulation. Additionally, the concentration of myosin light chain kinase and proteins engaged in calcium handling was measured in rat fast medial gastrocnemius muscle. After the training, the potentiation of twitch force and peak rate of force development was increased in FF but not FR MUs. Force potentiation of 40-Hz tetanic contractions was increased in both fast MU types. After the training, the twitch duration of FR MUs was decreased, and FF MUs were less prone to high-frequency fatigue during conditioning stimulation. Muscle concentration of triadin was increased, whereas concentrations of ryanodine receptor 1, junctin, FKBP12, sarcoplasmic reticulum calcium ATPase 1, parvalbumin, myosin light chain kinase, and actomyosin adenosine triphosphatase content were not modified. After short-term resistance training, the twitch contraction time and twitch:tetanus force ratio of FR MUs are decreased, and PTP ability is not changed. However, PTP capacity is increased in response to submaximal activation. In FF MUs increase in PTP ability coexists with lesser fatigability. Further work is required to find out if the increase in triadin concentration has any impact on the observed contractile response.
强直后增强（PTP）的力量取决于肌肉内的钙水平和敏感性，并且可能受到疲劳的影响。本研究的目的是确定在进行5周的自愿举重训练后，分离的快速抗疲劳（FR）和快速易疲劳（FF）运动单位（MU）对单次和40 Hz电刺激诱发的力量增强能力。通过逐渐增加（10 - 150 Hz）刺激频率诱发的强直收缩作为条件刺激。此外，还测量了大鼠快速内侧腓肠肌中肌球蛋白轻链激酶和参与钙处理的蛋白质的浓度。训练后，FF运动单位的抽搐力增强和力量发展峰值速率增加，而FR运动单位则没有。两种快速运动单位类型中40 Hz强直收缩的力量增强均增加。训练后，FR运动单位的抽搐持续时间缩短，并且在条件刺激期间FF运动单位不太容易出现高频疲劳。三联蛋白的肌肉浓度增加，而1型兰尼碱受体、连接蛋白、FKBP12、肌浆网钙ATP酶1、小清蛋白、肌球蛋白轻链激酶和肌动球蛋白腺苷三磷酸酶含量的浓度没有改变。短期抗阻训练后，FR运动单位的抽搐收缩时间和抽搐：强直力比值降低，PTP能力不变。然而，对次最大激活的反应中PTP能力增加。在FF运动单位中，PTP能力的增加与较低的疲劳性并存。需要进一步的研究来确定三联蛋白浓度的增加是否对观察到的收缩反应有任何影响。
