What Is Slow-Twitch Muscle Fibers?
Type I (ST): Slow oxidative; fatigue-resistant; low glycogen content; high mitochondrial and myoglobin content.
What Does It Do?
Used for long-lasting, low level force production, extremely long endurance activities and because of its ability to oxidize lactate the slow-twitch fibers are needed to recover between repeated bursts of high intensity intervals or activity.
Building A Bigger Aerobic Base
Studies have shown that with endurance training an increase in H-LDH enzymes has been found in slow twitch fibers. This enzyme plays a role in oxidizing lactate. It’s not unusual for an endurance athlete to have as much as 65 – 80% of aerobic base training annually. Depending on the distances of your races your ratio of aerobic base training can vary from 50 – 80%.
Now before you go and start piling up large amounts of volume the slow-twitch muscle fibers are not fatigue proof. They’re fatigue resistant and you should observe a gradual increase in volume. As you spend time in your zone 1 you may find your heart rate drops quicker between intervals and a drop in resting heart rate.
A training zone system is based on three physiological points; aerobic threshold, anaerobic threshold, and VO2 max. Understanding your response to exercise with physiological testing can help you identify your needs for development.