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An acoustic startle alters knee joint stiffness and neuromuscular control
Author(s) -
DeAngelis A. I.,
Needle A. R.,
Kaminski T. W.,
Royer T. R.,
Knight C. A.,
Swanik C. B.
Publication year - 2015
Publication title -
scandinavian journal of medicine and science in sports
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.575
H-Index - 115
eISSN - 1600-0838
pISSN - 0905-7188
DOI - 10.1111/sms.12315
Subject(s) - reflex , moro reflex , startle response , medicine , muscle stiffness , electromyography , knee joint , physical medicine and rehabilitation , vastus medialis , stiffness , anesthesia , physics , surgery , thermodynamics
Growing evidence suggests that the nervous system contributes to non‐contact knee ligament injury, but limited evidence has measured the effect of extrinsic events on joint stability. Following unanticipated events, the startle reflex leads to universal stiffening of the limbs, but no studies have investigated how an acoustic startle influences knee stiffness and muscle activation during a dynamic knee perturbation. Thirty‐six individuals were tested for knee stiffness and muscle activation of the quadriceps and hamstrings. Subjects were seated and instructed to resist a 40‐degree knee flexion perturbation from a relaxed state. During some trials, an acoustic startle (50 ms, 1000 Hz, 100 dB) was applied 100 ms prior to the perturbation. Knee stiffness, muscle amplitude, and timing were quantified across time, muscle, and startle conditions. The acoustic startle increased short‐range (no startle: 0.044 ± 0.011 N·m/deg/kg; average startle: 0.047 ± 0.01 N·m/deg/kg) and total knee stiffness (no startle: 0.036 ± 0.01 N·m/deg/kg; first startle 0.027 ± 0.02 N·m/deg/kg). Additionally, the startle contributed to decreased [vastus medialis ( VM ): 13.76 ± 33.6%; vastus lateralis ( VL ): 6.72 ± 37.4%] but earlier ( VM : 0.133 ± 0.17 s; VL : 0.124 ± 0.17 s) activation of the quadriceps muscles. The results of this study indicate that the startle response can significantly disrupt knee stiffness regulation required to maintain joint stability. Further studies should explore the role of unanticipated events on unintentional injury.