Building the metabolic base may indeed be the missing link to best in class performance. And often due to outside training time commitments, many prioritize high intensity training over lengthier long distance & slow steady work to forge this base. Intuitively, one would guess at least by the measure of misery, short, high intensity training sessions are more beneficial & time efficient than modes not encouraging intermittent bouts of nausea and oxygen starvation. Although prioritizing top end anaerobic work appears to be pragmatic approach, research supports that base training of the mitochondria at level 2 (defined shortly) is critical for metabolic health and fuel efficiency. Today we take a dive into the importance of how the body fuels muscles, the source, and how metabolites are regulated; ultimately dictating systemic ability of the muscles to produce work.
Training Zones:
Zone 1: Very Light 50-60% HR Max
Zone 2: Light 60-70% HR Max
Zone 3: Moderate 70-80% HR Max
Zone 4: Hard 80-90% HR Max
Zone 5: Maximum 90-100% HR Max
Mitochondrial Efficiency In Zone 2 Training: Increased reliance on fat as fuel & and reduced blood lactate. Elite trained athlete’s metabolism is calibrated to utilize higher amounts of fat rather than glucose as fuel during work. Subsequent lactate produced (lactate is a fuel not a waste product) is kept inside the cell and utilized as fuel; although as output increases, a portion of lactate will spill into the blood and is shuttled systemically to be used elsewhere. For lesser trained athletes, the transition from fat to glucose happens at lower levels of output and lactate threshold is reached quicker. Lactate is subsequently shuttled outside of the cell via the blood for re-uptake in greater amounts as the MCT 1 receptors are less developed inside the cell; creating fueling and acidity issues. In efficient mitochondria, there are increased receptor networks that allow the lactate to be kept locally and entered direct into the Krebs cycle for rapid ATP (fuel) production.
Facts:
- Majority of elite athletes train in zone 2 primarily.
- Tour de France Champion Training Reco: 70-80% training in zone 2 off season; periodizing closer to competition, athletes will add increased concentrations of high intensity metabolic training.
Zone 2 Training Defintion: Exercise intensity where the mitochondria is stressed the most. This intensity of training is characterized by primarily using Type 1 (slow twitch) muscles. In zone 2, fat is the primary fuel utilized (fat oxidation = less Co2 production compared to glucose; = less acidity). As exercise intensity increases, fat fuel usage declines sharply as glucose is titrated in as primary source. As intensity continues to ramp, glucose breakdown increases eventually resulting in oxygen falling behind of demand (recall that O2 is necessary for the breakdown of glucose in aerobic respiration). Lactate is subsequently produced and oxidized in the mitochondria via an alternative pathway. If training intensity continues to increase, lactate will eventually spill over into the blood where it is transported and used in other muscle tissues or liver. Zone 2 training mobilizes the body’s energetic metabolism to use fat as a fuel and stimulates production of increased transporters to keep lactate in the cell as opposed to being shuttled into the blood.
How to train in Zone 2:
- Relatively low intensity cardio work; jogging, biking, rowing, paddling etc.
- Intensity:
- RPE: 4-6. Should be able to maintain a conversation, albeit noticeably exerting.
- HR Ranges 70-80% of max (this can vary widely depending on training history & health)
- 3-4 days per week to develop mitochondrial efficiency
- 2 days per week to maintain mitochondrial efficiency
- 1-1.5 hours per training session
