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The VO2 slow component: relationship between plasma ammonia and EMG activity
Surendran Sabapathy1, Donald A Schneider, Norman R Morris
1School of Physiotherapy and Exercise Science, Gold Coast Campus, Griffith University, Queensland, Australia. S.Sabapathy@griffith.edu.au
Medicine and Science in Sports and Exercise
|September 24, 2005
Summary
Increased ammonia (NH3) and specific muscle fiber activation correlate with the oxygen uptake (VO2) slow component during exercise. This suggests type II muscle fibers play a key role in exercise intensity regulation.
Area of Science:
- Exercise Physiology
- Muscle Physiology
- Biochemistry
Background:
- The slow component of oxygen uptake (VO2) kinetics is linked to increased energy demand during sustained submaximal exercise.
- Type II muscle fiber recruitment is hypothesized to contribute to the VO2 slow component and is associated with elevated plasma ammonia (NH3) levels.
Purpose of the Study:
- To investigate the relationship between the VO2 slow component, plasma NH3 concentration, and electromyography (EMG) during constant-load cycling.
- To explore the role of type II muscle fiber activation in the development of the VO2 slow component.
Main Methods:
- Eight healthy adults performed 7 minutes of heavy constant-load cycling.
- VO2 kinetics were analyzed using a two-term exponential model.
- Plasma NH3 and vastus lateralis EMG were measured throughout the exercise bout.
Main Results:
- A significant VO2 slow component (561 +/- 52 mL.min-1) was observed.
- Plasma NH3 concentration increased significantly during exercise and correlated with the VO2 slow component amplitude (r=0.79, P<0.05).
- EMG spectral analysis indicated progressive type II muscle fiber recruitment.
Conclusions:
- The findings support the hypothesis that increased type II muscle fiber recruitment contributes to the VO2 slow component.
- Elevated plasma NH3 levels serve as a potential indicator of type II muscle fiber activation during the slow component phase.
- EMG changes further corroborate the progressive recruitment of type II muscle fibers during sustained exercise.