Department of Biomedical Sciences for Health (SCIBIS), Università degli Studi di Milano, Milan, ITALY.
Med Sci Sports Exerc. 2023 Mar 1;55(3):469-481. doi: 10.1249/MSS.0000000000003076. Epub 2022 Oct 27.
Voluntary activation (VA) determined by interpolation-twitch technique could be affected by the characteristics of the in-series elastic components. To overcome this possible bias, a novel approach based on the mechanomyographic (MMG) signal to detect voluntary activation (VA MMG ) has been proposed. We examined the changes in VA and VA MMG after passive stretching to check the influence of neural and mechanical factors in the force output.
Twenty-six healthy men underwent VA assessment using the interpolated-twitch technique before and after unilateral passive stretching of the plantarflexors (five 45-s on + 15-s off). In addition to the force signal, the MMG signal was detected on gastrocnemius medialis, gastrocnemius lateralis, and soleus. From the force and MMG signal analysis, VA and VA MMG were calculated in the stretched and contralateral nonstretched limbs. Joint passive stiffness was also defined.
In the stretched limb, passive stretching increased dorsiflexion range (mean ± SD = +18% ± 10%, P < 0.001, ES = 1.54) but reduced joint passive stiffness (-22% ± 8%, P < 0.001, ES = -1.75), maximum voluntary contraction (-15% ± 7%, P < 0.001, ES = -0.87), VA (-7% ± 3%, P < 0.001, ES = -2.32), and VA MMG (-5% ± 2%, P < 0.001, ES = -1.26/-1.14). In the contralateral nonstretched limb, passive stretching increased dorsiflexion range (+10% ± 6%, P < 0.001, ES = 0.80) but reduced joint passive stiffness (-3% ± 2%, P = 0.041, ES = -0.27), maximum voluntary contraction (-4% ± 3%, P = 0.035, ES = -0.24), VA (-4% ± 2%, P < 0.001, ES = -1.77), and VA MMG (- 2% ± 1%, P < 0.05, ES = -0.54/-0.46). The stretch-induced changes in VA correlated with VA MMG ( R ranging from 0.447 to 0.583 considering all muscles) and with joint passive stiffness (stretched limb: R = 0.503; contralateral nonstretched limb: R = 0.530).
VA output is overall influenced by both neural and mechanical factors, not distinguishable using the interpolated-twitch technique. VA MMG is a complementary index to assess the changes in VA not influenced by mechanical factors and to examine synergistic muscles.
通过插值-抽搐技术确定的自愿激活（VA）可能受到串联弹性元件特性的影响。为了克服这种可能的偏差，提出了一种基于肌电图（MMG）信号检测自愿激活（VA MMG）的新方法。我们检查了被动伸展后 VA 和 VA MMG 的变化，以检查神经和机械因素对力输出的影响。
26 名健康男性在单侧足底屈肌被动伸展（5 次 45 秒+15 秒休息）前后使用插值-抽搐技术进行 VA 评估。除了力信号外，还在腓肠肌内侧、腓肠肌外侧和比目鱼肌上检测 MMG 信号。从力和 MMG 信号分析中，计算伸展和对侧非伸展肢体的 VA 和 VA MMG。还定义了关节被动刚度。
在伸展肢体中，被动伸展增加了背屈范围（平均值±标准差=+18%±10%，P<0.001，ES=1.54），但降低了关节被动刚度（-22%±8%，P<0.001，ES=-1.75）、最大自主收缩（-15%±7%，P<0.001，ES=-0.87）、VA（-7%±3%，P<0.001，ES=-2.32）和 VA MMG（-5%±2%，P<0.001，ES=-1.26/-1.14）。在对侧非伸展肢体中，被动伸展增加了背屈范围（+10%±6%，P<0.001，ES=0.80），但降低了关节被动刚度（-3%±2%，P=0.041，ES=-0.27）、最大自主收缩（-4%±3%，P=0.035，ES=-0.24）、VA（-4%±2%，P<0.001，ES=-1.77）和 VA MMG（-2%±1%，P<0.05，ES=-0.54/-0.46）。VA 的拉伸诱导变化与 VA MMG（考虑所有肌肉时 R 值范围为 0.447 至 0.583）和关节被动刚度（伸展肢体：R=0.503；对侧非伸展肢体：R=0.530）相关。
VA 输出总体上受到神经和机械因素的影响，不能通过插值-抽搐技术区分。VA MMG 是一种补充指标，可用于评估不受机械因素影响的 VA 变化，并检查协同肌肉。
