Another Way to Confuse Motor Control: Manual Technique Supposed to Shorten Muscle Spindles Reduces the Muscular Holding Stability in the Sense of Adaptive Force in Male Soccer Players

Frank N Bittmann; Silas Dech; Laura V Schaefer

doi:10.3390/brainsci13071105

Another Way to Confuse Motor Control: Manual Technique Supposed to Shorten Muscle Spindles Reduces the Muscular Holding Stability in the Sense of Adaptive Force in Male Soccer Players

Brain Sci. 2023 Jul 21;13(7):1105. doi: 10.3390/brainsci13071105.

Authors

Frank N Bittmann¹, Silas Dech^{1

2}, Laura V Schaefer^{1

2}

Affiliations

¹ Regulative Physiology and Prevention, Department Sports and Health Sciences, University of Potsdam, 14476 Potsdam, Germany.
² Health Education in Sports, Department Sports and Health Sciences, University of Potsdam, 14476 Potsdam, Germany.

Abstract

Sensorimotor control can be impaired by slacked muscle spindles. This was shown for reflex responses and, recently, also for muscular stability in the sense of Adaptive Force (AF). The slack in muscle spindles was generated by contracting the lengthened muscle followed by passive shortening. AF was suggested to specifically reflect sensorimotor control since it requires tension-length control in adaptation to an increasing load. This study investigated AF parameters in reaction to another, manually performed slack procedure in a preselected sample (n = 13). The AF of 11 elbow and 12 hip flexors was assessed by an objectified manual muscle test (MMT) using a handheld device. Maximal isometric AF was significantly reduced after manual spindle technique vs. regular MMT. Muscle lengthening started at 64.93 ± 12.46% of maximal voluntary isometric contraction (MVIC). During regular MMT, muscle length could be maintained stable until 92.53 ± 10.12% of MVIC. Hence, muscular stability measured by AF was impaired after spindle manipulation. Force oscillations arose at a significantly lower level for regular vs. spindle. This supports the assumption that they are a prerequisite for stable adaptation. Reduced muscular stability in reaction to slack procedures is considered physiological since sensory information is misled. It is proposed to use slack procedures to test the functionality of the neuromuscular system, which is relevant for clinical practice.

Keywords: holding capacity; maximal isometric Adaptive Force; motor control; muscle instability; muscle physiology; muscle spindle; muscle stability; neuromuscular control; neuromuscular functioning; regulatory physiology.

Grants and funding

This research received no external funding. The publication was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—Project no. 491466077.