| Effects
of Isometric and Isotonic Exercise on Hindlimb Unloaded Induced Muscle
Atrophy
Mark
England
Marquette
University
Milwaukee,
WI
Mentor:
Dr. Robert Fitts
One
of the primary concerns with extended spaceflight is the atrophy associated
with the skeletal muscle of the legs, especially the slow fibers of the
soleus (Hurst). In this study, as a simulation of the microgravity environment
experienced during spaceflight, rats were subjected fourteen days of hindlimb
unloading (HU), thus inducing muscle atrophy. The aim of this study was
to combat this experienced atrophy by subjecting the rats to an exercise
routine consisting of once daily bouts of isotonic (a.m.) and isometric
(p.m.) exercise. Previous studies which have aimed to protect the soleus
have only used either isotonic or isometric exercise (Hurst). Although
both types of exercise have showed some muscle protection, improvement
remains possible. With a routine involving both isotonic and isometric
exercise, we hope to maximally protect the soleus.
In
order to determine the protection provided by the exercise routine, the
contractile properties of the soleus are measured in situ. Under anesthesia,
debates have arisen of whether or not administration of O2 through a trachea
tube is beneficial in preventing muscle fatigue. By completing the in situ
routine on several rats with and without oxygen, results show that rats
given oxygen during the routine exhibited a lower relative fatigue than
those not given additional oxygen.
Finally,
it is known that as muscles atrophy, a concomitant rise in glycogen is
observed. In our study, the control rats showed a glycogen concentration
of 2.65 +/- 0.98 mg/g, while the unloaded rats had a 4.39 +/- 0.99 mg/g
glycogen concentration. Further, upon stimulation, an increase in the lactic
acid concentration in the muscle should occur as the muscle fatigues. In
our study, we found the lactic acid concentration of the unstimulated soleus
to be 5.23 +/- 2.30 umoles/g, while the stimulated muscle was 8.37 +/-
2.60 umoles/g. |
