Shimano Xtr M9000, M9100, series bike groupset, derailleur adaptor, Shimano pedals. The science is clear: The optimal training recipe for endurance fitness includes work at low, moderate, and high intensities. These are the ingredients of an effective triathlon training program. Our next step is to determine the right proportions—in other words, to figure out how to balance these three intensities for best results. Science helps us here, too.

Shimano Xtr M9000, Bike Adaptor, Pedals

Shimano, XTR M9000 I-Spec II Adaptor Unit Right

Shimano Xtr M9000
i spec ii

Shimano, XTR PD-M9100 SPD Bike Pedals 3mm Shorter Length Axle, Aluminum

Shimano Xtr Pd
m9100 spd bike

Shimano, XTR PD-M9120 SPD Bike Pedals Standard Length Axle, Aluminum

Shimano Xtr Pd
m9120 spd bike

Each exercise intensity—low, moderate, and high—has what’s known as a dose response relationship with endurance fitness. This simply means that the degree to which a given intensity affects endurance performance depends on the amount of exercise you do at that intensity. For example, you wouldn’t expect 1 minute per day of moderate-intensity exercise to produce the same results as 20 minutes per day at the same intensity. The maximally effective dose of a certain intensity is the amount of it that fully realizes the potential benefits of training at that intensity. Think of it as the Goldilocks Zone: neither too little nor too much, but just right to actualize 100 percent of that intensity’s potential to enhance endurance fitness.

Shimano, XTR RD-M9000 11SP Derailleur GS Cage, Medium Cage

Shimano Xtr Rd
m9000 11sp derailleur

Shimano, XTR SL-M9100 I-Spec Ev Shifter Front, Left, 2 Speed, I-Spec Ev

Shimano Sl
m9100 i spec

Shimano, XTR SL-M9100 Shifter Rear, Right, 22.2mm Band Clamp

Shimano Sl
m9100 shifter rear

Shimano Bike groupset M9100, Optimal training recipe for endurance fitness

Each specific intensity has its own dose-response curve, meaning the maximally effective dose of low-intensity exercise is not the same as the maximally effective doses of moderate and high intensity exercise. In our effort to identify the optimal balance of training intensities, therefore, it’s useful to look at the maximally effective dose of each.

As a general principle, the higher the intensity of exercise, the more stressful it is to the body and the less of it the body can tolerate. But stress does not increase linearly with intensity. There is evidence that an abrupt jump in stressfulness occurs at the ventilatory threshold, which, you will recall, marks the boundary between low intensity and moderate intensity.

This appears to happen because the brain is required to activate large numbers of fast-twitch muscle fibers when this threshold is crossed. As a result, it takes the nervous system longer to recover following workouts that include work at or above the VT.

Evidence of this comes from another study led by the 80/20 Rule’s discoverer, Stephen Seiler. Nine highly trained runners and eight fit young nonathletes were required to complete a series of runs, some of them below the ventilatory threshold (low intensity), others right at the VT (moderate intensity), and one above it (high intensity). After each workout, Seiler and his colleagues measured heart rate variability (subtle variations in the heart’s rhythm), which is an indicator of stress in the autonomic nervous system, a key player in postexercise recovery.

They found that even after two hours of low-intensity running, autonomic stress was minimal, whereas both moderate-intensity and high-intensity running increased stress markers significantly and equally. The lesson for athletes like you is that the optimal training recipe for endurance fitness combines large amounts of low intensity work with relatively small amounts of work at moderate and high intensities. But you can’t make a good cake with vague measurements like “large” and “small” you need quantitative measurements and the same is true of endurance training.

It is not possible to derive the specific intensity ratios that yield the best results from biochemistry, however. Because the optimal dose of each intensity is affected by training done at other intensities, answering the question of how best to combine these ingredients demands that we broaden our focus and look at the effects of different intensity ratios on fitness and performance in real athletes. Fortunately, this has been done.

Shifter, Chainring, Brake, Derailleur