2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
ENERGY CONSUMPTION IS POSITIVELY CORRELATED TO
SALIVARY NEUROPEPTIDE Y DURING MILITARY TRAINING IN
COLD WEATHER
Harri Lindholm 1 , , Ari Hirvonen 1 , Sirpa Hyttinen 1 , Raija Ilmarinen 1 , Heli Sistonen 1 , Matti
Santtila 2 , Heikki Rusko 3
1 Finnish Institute of Occupational Health (FIOH), Helsinki, Finland
2 Defence Staff, Finnish Defence Forces, Helsinki, Finland
3 Jyväskylä University, Helsinki, Finland
Contact person: harri.lindholm@ttl.fi
INTRODUCTION
The maintenance of energy balance during military work in cold environments is fundamental
to functional capacity. Food intake is regulated by a complex neuronal and hormonal network,
which is affected by the thermal environment, physical workload, and mental stress.
Neuropeptide Y (NPY) is an important orexigenic hormone. The excretion of NPY is
activated in hunger center when the need of energy intake is increasing and deactivated when
the energy balance has been stabilized (Konturek et al. 2005). NPY has also been reported to
reflect mental stress balance. During uncontrollable acute psychological stress, the levels of
NPY release are reduced (Morgan et al. 2002). Modern techniques of heart rate (HR) and
heart rate variability (HRV) analyses have improved the opportunities to estimate physical
activity and energy consumption indirectly (Saalasti 2003). In field studies, combining
various non-invasive methods allows us to collect a larger body of data concerning energy
balance during environmentally demanding operations. In this study, we evaluated the
associations between the estimated energy consumption and hormonal responses of healthy
young men during military operations in a cold environment.
METHODS
Subjects. The study group consisted of 13 young and healthy conscripts (Table 1). Their body
composition was analysed by the whole body impedance method (InBody 330, Biospace,
South Korea). Maximal oxygen consumption (VO2max) and individual HR and HRV
responses were measured through an exercise test on a treadmill (Vmax, SensorMedics,
USA). The treadmill running was continued until exhaustion. The laboratory measurements
were performed after five months military service and three weeks before the field exercise.
The research protocol was reviewed and approved in advance by the Institutional Research
Committee and the Coordinating Ethics Committee of the Hospital District of Helsinki and
Uusimaa (Finland). The subjects gave written informed consent before the experimental
sessions and were not paid for their participation.
Table 1. Physical characteristics of the subjects.
580
Age,
years
Height,
cm
Weight,
kg
Fat percentage,
%
VO2max
ml/kg·min -
1
Mean 19.7 179.6 74.1 13.0 49.9
±SD 0.8 6.0 8.9 1.6 2.5
Range 19─21 173─192 63─88 9.9─17.1 40.2─57.9
Experimental design. The conscripts participated in a two-week combat exercise in
December, and the field measurements were made during the rehearsal. The weather was cold