Ambient temperature and neck EMG with +Gz loading on a trampoline.
BACKGROUND
Fighter pilots who are frequently exposed to severe cold ambient temperatures experience neck pain disabilities and occupational disorders more often than those who are not so exposed. We hypothesized that a cold-induced increase in muscle strain might lead to in-flight neck injuries. The aims of this study were to measure the level of cooling before takeoff and to determine muscle strain under Gz loading (0 to +4 Gz) at different temperatures.


METHODS
Test subjects' (n = 14) skin temperature (T(skin)) over the trapezoids was measured before the walk to the aircraft and again in the cockpit (air temperature -14 degrees C). The subjects then performed trampoline exercises in two different ambient temperatures (-2 degrees C and +21 degrees C) after a 30-min period at the respective temperatures. EMG activity of the sternocleidomastoid (SCM), cervical erector spinae (CES), trapezoid (TRA), thoracic erector spinae (TES) muscles, and Tskin of the SCM and TRA were measured.


RESULTS
Tskin over the trapezoids decreased from 30.1 +/- 1.7 degrees C to 27.8 +/- 2.6 degrees C (p < 0.001) before takeoff. The change of muscle strain in cold was +11.0% in SCM, +14.9% in CES, +3.7% in TRA, and -1.7% in TES. Change was statistically significant in the cervical, uncovered area (SCM, CES). The linear regression model indicated a 2.6% increase in muscle strain per every decreased degree centigrade in skin temperature over the SCM.


CONCLUSIONS
Superficial cooling over the neck muscles was significant prior to takeoff. Muscle loading in the cold caused higher EMG activity. A major increase in muscle strain was seen in the cervical muscles. These findings suggest a cold-induced increase in muscle strain during in-flight Gz loading.
Sovelius
Roope
R
Training Air Wing, P.O. Box 5, FIN-62201 Kauhava, Finland. roope.sovelius@mil.fi
Oksa
Juha
J
Rintala
Harri
H
Huhtala
Heini
H
Siitonen
Simo
S
D000328:Adult; D000337:Aerospace Medicine; D003080:Cold Temperature / Q000009:adverse effects*; D004576:Electromyography; D005260:Female; D005387:Finland; D006801:Humans; D018471:Hypergravity; D008297:Male; D008889:Military Personnel; D009129:Muscle Tonus / Q000502:physiology*; D009334:Neck Muscles / Q000293:injuries / Q000503:physiopathology*; D012621:Seasons; D012881:Skin Temperature / Q000502:physiology*