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Adjustments of cardiac function during prolonged exercise relative to lactate threshold
H S Kim1, K Tanaka, Y Kumazaki
1Korea Sport Science Institute.
Summary
Healthy males maintained cardiac contractility during prolonged exercise at lactate threshold (LT). Stroke volume and myocardial contractility remained stable, demonstrating a "contractility reserve" despite significant changes in heart rate and oxygen uptake.
Area of Science:
- Cardiovascular Physiology
- Exercise Physiology
Background:
- Prolonged submaximal exercise can alter cardiac function.
- Understanding cardiac response relative to lactate threshold (LT) is crucial for exercise science.
Purpose of the Study:
- To evaluate changes in cardiac function during prolonged submaximal exercise at LT intensity.
- To investigate the concept of
- contractility reserve
- during endurance exercise.
Main Methods:
- Seven healthy males aged 30.3 ± 5.7 years participated.
- Cardiac function assessed using electrocardiogram, phonocardiogram, and impedance cardiogram.
- Stroke volume (SV) determined via Kubicek method; systolic time intervals analyzed.
Main Results:
- Stroke volume (SV) and myocardial contractility indices (MSER, PEP/LVET) remained unchanged during 40-min cycling.
- Heart rate and oxygen uptake showed statistically significant increases.
- Systolic blood pressure remained relatively stable throughout the exercise.
Conclusions:
- The study suggests a "contractility reserve" in healthy individuals during prolonged exercise at LT.
- Cardiac muscle maintains contractility despite increased physiological demands.
- Findings support the ability to sustain cardiac performance during moderate-intensity endurance activities.