2007, Piran, Slovenia

Occupational Thermal Problems
EFFECT OF COOLING ON UPPER ARM MOVEMENTS DURING A
REPETITIVE TASK
Hugo Piedrahita 1 , Juha Oksa 2 , Hannu Rintamäki 2 , Erja Sormunen 2 and Christer Malm 1,3
1
Luleå University of Technology, Luleå, Sweden
2
Finnish Institute of Occupational Health, Laboratory of Physiology, Oulu, Finland
3
The Muscle Research Group, Anatomy section, Umeå University, Sweden
Contact person: hugo.piedrahita@ltu.se
INTRODUCTION
Although has been demonstrated that cooling deteriorate all parameters of the muscular
performance, less studies has been performed to test the effect of cooling on the coordination
and direction of the upper arm movement. In one study Meigal A.Y. et al. 1998 found that the
voluntary movements and postural can be affected by cold shivering. Mäkinen T. et al. (2005)
demonstrated measuring the postural sway between healthy subjects, that postural control is
impaired in cold conditions. They established that that the subjects had to perform more
corrective movements in the cold due to changes in their sensory functions or neuromuscular
control. In other study Oksa J. et al. (1997), found that in comparison with thermoneutral
conditions, the exposure to cold increased the duration of the contact, stretch and shortening
phases and take-off velocity of the subjects performing a maximal rebound jump, leading to
decreased muscle performance. The increased level of co-contraction of the agonistantagonist
muscle pair and decreased activity of the agonist muscle during shortening phase
may in part explain the decreased muscle performance found.
This study was designed to investigate the effects of cooling on upper arm motion trajectories
during handling repetitive light weights in a horizontal plane. We hypothesised that
performing manual task repeatedly in cold conditions can lead to increase the muscular strain,
which induce changes in the motor coordination (multi-joint trajectories) to minimize the heat
loss and assure an economical activation of the fatiguing muscles. These changes could be
traduced in a high risk for musculoskeletal disorders in the long term.
METHODS
Ten healthy female subjects volunteer for the study. They performed one-handed repetitive
task while standing in front of a table during one hour. Six small boxes weighting 0.5 kg each
were used such as objects to move. Six different angles destinations between 30º and 220º
were established. The task was performed in two different conditions: 10ºC (Cold condition)
and 25ºC (Neutral condition). Two video cameras (front and lateral) were used for recording
the movement trajectories of the head, shoulder, elbow, wrist and hip on the right side of the
body. The data were digitalized and processed using automatic tracking of objects in an image
sequencing software, WinAnalize. Figure 1 shows the schematic representation of the set-up
experiment.
RESULTS
At the end of the working period in all anatomic reference points at Cold condition the
estimated area under the curve (AUC) of the x/y ratios during one complete cycle (20
seconds) was higher compared with Neutral, with exception of the Wrist where we found a
small decreased. Significant differences were found only at the Elbow level, Table 1. The
differences of the areas were affected by the “y” axe predominantly. We observed also than in
Cold condition the estimated AUC in Cold condition was higher at the end (60 minute)
compared with the first minute in all anatomic references points except at the Wrist level
where a small decreased was observed.
599