Human Performance Lab, Faculty of Kinesiology, University of Calgary, 2500 University Drive NW, Calgary, AB, T2N 1N4, Canada.
Human Health and Nutritional Sciences, College of Biological Sciences, University of Guelph, 50 Stone Rd E, Guelph, ON, N1G 2W1, Canada.
Eur J Appl Physiol. 2018 May;118(5):1063-1077. doi: 10.1007/s00421-018-3840-0. Epub 2018 Mar 8.
We examined how muscle length and time between stimuli (inter-pulse interval, IPI) influence declines in force (sag) seen during unfused tetani in the human adductor pollicis muscle.
A series of 16-pulse contractions were evoked with IPIs between 1 × and 5 × the twitch time to peak tension (TPT) at large (long muscle length) and small (short muscle length) thumb adduction angles. Unfused tetani were mathematically deconstructed into a series of overlapping twitch contractions to examine why sag exhibits length- and IPI-dependencies.
Across all IPIs tested, sag was 62% greater at short than long muscle length, and sag increased as IPI was increased at both muscle lengths. Force attributable to the second stimulus increased as IPI was decreased. Twitch force declined from maximal values across all IPI tested, with the greatest reductions seen at short muscle length and long IPI. At IPI below 2 × TPT, the twitch with highest force occurred earlier than the peak force of the corresponding unfused tetani. Contraction-induced declines in twitch duration (TPT + half relaxation time) were only observed at IPI longer than 1.75 × TPT, and were unaffected by muscle length.
Sag is an intrinsic feature of healthy human adductor pollicis muscle. The length-dependence of sag is related to greater diminution of twitch force at short relative to long muscle length. The dependence of sag on IPI is related to IPI-dependent changes in twitch duration and twitch force, and the timing of peak twitch force relative to the peak force of the associated unfused tetanus.
我们研究了肌肉长度和刺激时间间隔（刺激间间期，IPI）如何影响人拇指内收肌未融合强直收缩中观察到的力下降（松弛）。
在大（长肌肉长度）和小（短肌肉长度）拇指内收角，用 IPIs 在 1×到 5×肌强直时间至峰值张力（TPT）之间诱发一系列 16 脉冲收缩。通过将未融合强直收缩数学分解为一系列重叠的单次收缩，来研究为什么松弛表现出长度和 IPI 依赖性。
在所有测试的 IPI 下，短肌肉长度时的松弛比长肌肉长度时大 62%，并且在两种肌肉长度下，松弛随着 IPI 的增加而增加。第二刺激的力随着 IPI 的减少而增加。在所有测试的 IPI 下，单次收缩力从最大值下降，在短肌肉长度和长 IPI 时下降最大。在 IPI 低于 2×TPT 时，具有最高力的单次收缩比相应的未融合强直收缩的峰值力更早出现。只有在 IPI 长于 1.75×TPT 时，才会观察到收缩诱导的单次收缩时程（TPT+半松弛时间）下降，并且不受肌肉长度的影响。
松弛是健康人拇指内收肌的固有特征。松弛的长度依赖性与短肌肉长度相对于长肌肉长度时单次收缩力下降更大有关。松弛对 IPI 的依赖性与 IPI 依赖性的单次收缩时程和单次收缩力变化以及峰值单次收缩力相对于相关未融合强直收缩的峰值力的时间有关。
