We examined if transcranial magnetic stimulation (TMS) is a valid tool for assessment of voluntary activation of the knee extensors in healthy individuals. Maximal M-waves (M_max) of vastus lateralis (VL) were evoked with electrical stimulation of femoral nerve (FNS); M_max of medial hamstrings (HS) was evoked with electrical stimulation of sciatic nerve branches; motor evoked potentials (MEPs) of VL and HS were evoked with TMS; superimposed twitches (SIT) of knee extensors were evoked with FNS and TMS. In Study 1, TMS intensity (69% output(SD 5)) was optimized for MEP sizes, but guidelines for test validity could not be met. Agonist VL MEPs were too small (51.4% M_max(SD 11.9); guideline ≥70% M_max) and antagonist HS MEPs were too big (16.5% M_max(SD 10.3); guideline <10% M_max). Consequently, the TMS estimated resting twitch (99.1 N(SD 37.2)) and FNS resting twitch (142.4 N(SD 41.8)) were different. In Study 2, SITs at 90% maximal voluntary contraction (MVC) were similar between TMS (16.1 N(SD 10.3)) and FNS (20.9 N(SD 16.7)), when TMS intensity was optimized for this purpose, suggesting a procedure that combines TMS SITs with FNS resting twitches could be valid. In Study 3, which tested the TMS intensity (56% output(SD 18)) that evoked the largest SIT at 90%MVC, voluntary activation from TMS (87.3%(SD 7.1)) and FNS (84.5%(SD 7.6)) were different. In sum, the contemporary procedure for TMS-based voluntary activation of the knee extensors is invalid. A modified procedure improves validity, but only in individuals who meet rigorous inclusion criteria for SITs and MEPs.

中文翻译：

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经颅磁刺激自愿激活膝关节伸肌

我们检查了经颅磁刺激（TMS）是否是评估健康个体中膝关节伸肌自愿激活的有效工具。股神经（FNS）刺激诱发股外侧肌（VL）的最大M波（M _max）；中号_最大内侧腿筋（HS）与坐骨神经分支的电刺激诱发; TMS诱发VL和HS的运动诱发电位（MEP）；FNS和TMS诱发膝关节伸肌的叠加抽搐（SIT）。在研究1中，针对MEP大小优化了TMS强度（69％的输出（SD 5）），但无法满足测试有效性的准则。激动剂VL MEP太小（_最大51.4％M （SD 11.9）;准则≥70％M_最大）和拮抗剂HS MEP太大（_最大16.5％M （SD 10.3）;指南<10％M _max）。因此，TMS估计静息抽搐（99.1 N（SD 37.2））和FNS静息抽搐（142.4 N（SD 41.8））不同。在研究2中，当为此目的优化了TMS强度时，TMS（16.1 N（SD 10.3））和FNS（20.9 N（SD 16.7））处于最大自愿收缩（MVC）90％的SIT相似。将TMS SIT与FNS静止抽搐结合使用可能是有效的。在研究3中，测试了TMS强度（56％的输出（SD 18）），其最大的SIT为90％MVC，TMS的自愿激活（87.3％（SD 7.1））和FNS（84.5％（SD 7.6））是不同的。总而言之，当代基于TMS的膝关节伸肌主动激活程序无效。修改后的程序可以提高有效性，但仅限于符合SIT和MEP严格纳入标准的个人。