2007, Piran, Slovenia

Altitude Physiology
ANALYSIS OF MUSCLE ACTIVITY DURING TREADMILL
WALKING IN A NORMOBARIC HYPOXIA ENVIRONMENT
Takayuki Watanabe 1 , Takeshi Sato 2 , Tasuku Miyoshi 3 , Shoji Igawa (1 , Akira Horii 1
1 Graduate School of Health and Sport Science Nippon Sport Science University,
Tokyo; 2 Jissen Women’s University, Tokyo; 3 Shibaura Institute of Technology,
Saitama, Japan
Contact person: nabetaka@nittai.ac.jp
INTRODUCTION
In recent years, in Japan, the opportunity for middle- and old aged individuals to
participate in mountain hiking has increased. They often climb mountains on day trips
and can reach peaks as high as 3000 m above sea level.
Fulco et al. (1994) investigated the effect of acute and chronic exposure to an altitude
of 4300 m on muscle voluntary construction (MVC) and muscle fatigue of the
adductor pollicis muscle. They observed a significant decrease in time to exhaustion
for 50% MVC during acute hypoxia.
Based on the suggestions of Shinohara et al. (1992) regarding the recruitment of
motor units during heavy exercise, we hypothesised that muscle activity and the
associated fatigue would be different for the same level of activity in a normoxic
compared to a hypoxic environment. We therefore investigated the activity of muscles
during walking in a normobaric hypoxic environment.
METHODS
Subjects
Seven healthy male subjects [average (SD) age: 22.00 (2.8) yrs, mass: 65.14 (5.18)
kg, height: 1.73 (0.06) m] volunteered for the experiments. All subjects were right-leg
dominant. Informed consent to participate in this study was obtained by all subjects.
Experimental arrangement
Subjects walked on a treadmill (Biomill, S & ME, Japan) at different speeds (2-6
km/h) for five minutes at each speed. They were asked to swing their arms normally.
Prior to the experimental trials, subjects practiced walking on the treadmill for a few
minutes at different speeds. During the experimental trials, subjects were requested to
walk at 2, 4 and 6 km/h so that we could compare walking at the same speeds in
normoxic and hypoxic environments. Subjects were exposed to a normobaric hypoxic
environment, where the oxygen concentration in the chamber was maintained at
14.5% O2, thus simulating an equivalent altitude of 3000 m.
Electromyograms (EMG)
EMG signals were recorded from the following muscles on the right side: vastus
medialis (VM), biceps femoris (BF), tibiralis anterior (TA), medial head of
gastrocnemius (MG), and soleus (SOL), and cross-talk was minimized between
muscle groups. EMGs of each muscle were obtained using silver-silver chloride
bipolar surface electrodes. Prior to attaching the electrodes, skin electrical resistance
was minimised by shaving the area of electrode placement and cleaning the skin using
alcohol pads (Nihon Kohden, Japan). Surface electrodes were placed 2 cm apart over
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