Time and intensity add up to workload, and all other things being equal, too little training time means there’s an insufficient training stimulus. That’s when it hit me. We had found the point at which the classic endurance training model breaks down. Once you get below 8 hours of training a week, the old tried-and-true methods derived from pro-level athletes no longer work.

The end product of all three systems is ATP, which releases energy when one of its three phosphate bonds is broken. The resulting adenosine diphosphate is then resynthesized to ATP so it can be broken again, and again, and again.

The aerobic system is the body’s primary source of energy, and it’s an utterly amazing machine. It can burn carbohydrate, fat, and protein simultaneously and can regulate the mixture it burns based on fuel availability and energy demand. It’s a flex-fuel engine that’s remarkably clean and efficient; when the aerobic system is done with a molecule of sugar, the only waste products are water and carbon dioxide. In comparison, the glycolytic system (discussed below) produces energy faster, but it can only use carbohydrate, produces less ATP from every molecule of sugar it processes, and produces lactate as a byproduct (more on this later).

Lactate is a partially used carbohydrate that leads to trouble when it builds up in your muscles. The molecule is created as a normal step of aerobic metabolism, and lactate is constantly being recycled back into usable energy. The problem isn’t that more lactate is being produced; instead, as exercise intensity increases, you reach a point where lactate removal or processing can no longer keep up with production.

What ultimately happens to these lactate leftovers? Lactate has gotten a bad rap for years. It has been blamed for the burning sensation in your muscles when you surge above your sustainable pace. It has been blamed for delayed-onset muscle soreness. People have tried to massage it away, flush it out, and buffer it. But the best way to get rid of lactate is to reintegrate it back into the normal aerobic metabolism to complete the process of breaking it down into energy, water, and carbon dioxide. One of the key adaptations you’re seeking as an endurance athlete is an improvement in your ability to get that lactate integrated back into the normal process of aerobic energy production so it can be oxidized completely. The faster you can process lactate, the more work you can perform before lactate levels in your muscles and blood start to rise, and the faster you can recover from hard efforts. There’s

Rather than seeing your various energy pathways as separate and distinct, it’s better to think of them as segments of one continuous string, arranged based on the amount of energy derived from each. At one end is a large segment representing the aerobic system, which theoretically could power your muscles at a moderate intensity level forever if it had sufficient oxygen and fuel. After that is the glycolytic system, which can do a lot of work but can run at full tilt for a limited time before you will have to reduce your exercise intensity. Finally, there is the segment for VO2max, which is the maximum amount of work you can do but represents an intensity that is sustainable for only a few minutes. We can put the small but powerful contribution from the immediate energy system (ATP/CP) in this region, too, since it powers maximal efforts that are only a few seconds long. Improving fitness in one system is like lifting the string in that region—all other areas of the string rise, too. The extents of these ancillary improvements vary, based on the system you initially targeted.

When you view the energy systems as interconnected parts of the same string, it starts to make sense that when training pulls up on the VO2max end of the string, you’ll see a subsequent increase in performance from the aerobic and glycolytic systems. To use an old phrase, a rising tide lifts all boats.

TIME-CRUNCHED TRAINING LEADS TO TIME-CRUNCHED FITNESS: The TCTP is a limited-time offer. You will gain fitness and power rapidly, and you will be able to have a lot of fun with it while it lasts, but 10 to 12 weeks after you start the program, you’ll have to back off and recover. This program can be used two or three times in a 12-month period, but you should not run through the 11 weeks and then immediately start over at week 1.

Another reason I was won over by this program was that because the high-intensity intervals build aerobic fitness as well as power at lactate threshold and VO2max, many athletes who use the TCTP two or three times in a 12-month period get incrementally stronger each time.

So although the TCTP is a relatively short-term, high-intensity, low-volume training program, it produces lasting performance gains and gives athletes the opportunity to continue growing stronger season after season.

The pattern linking the rise and fall of named diets begins with a strategy that focuses on whole foods and somehow restricts energy intake. The strategy works, people feel great and lose weight. Foods and supplements are developed to make compliance more convenient, but these shift people back to old habits of consuming fewer whole foods. The packaged foods and supplements contribute to increased caloric intake, people regain weight, and once the positive results have disappeared their compliance diminishes and they return to their normal food choices and eating behaviors. As soon as you see “keto-cookies,” it’s over.

In terms of total amounts, your goal within the first 2 hours after exercising should be to consume 500 to 700 milligrams of sodium and enough water to equal 1.5 times the water weight you lost during the exercise session. In other words, if you lost 2 pounds (32 ounces, or 0.9 kg) during your ride, you should drink 48 ounces of fluid (about 1.4 liters) in the 2 hours after you get back. Within 4 hours after training, you should consume 1.5 grams of carbohydrate per kilogram (g/kg) of body weight.

A small snack (25 to 35 grams of carbohydrate, or about 1 ounce) in the hour before a 60-minute workout staves off hunger and keeps you alert and focused, while the carbohydrate you have stored in your muscles takes care of the actual fuel for training.

To get carbohydrate from the intestine into the blood, you need to have enough water in the intestine to facilitate the transport. If you don’t, the food sits there until enough water becomes available, either because you drink more or because it is pulled from your body into your intestine. This latter mechanism isn’t ideal in any circumstance, but it is not a big problem when you are at rest and well hydrated. When you are exercising and pumping sweat onto your skin to cool off, however, your body prioritizes thermoregulation over digestion, and digestion slows dramatically.

Dehydration lowers plasma volume because the sweat on your skin was most recently plasma in your blood.

As blood volume decreases, your heart rate increases in an effort to meet your oxygen demands with less fluid available to circulate. But stroke volume—the volume your heart pumps with each beat—also decreases when plasma volume decreases, and Wingo et al. (2012) have shown that a reduction in stroke volume correlates with a proportional reduction in VO2max.

Inflammation associated with trauma or injury is different than inflammation as a response to normal exercise. Following a hard ride or run, you will have some inflammation in working muscles. But that inflammation may be a key component of the training stress that results in adaptation and progress. When you immediately jump into an ice bath following a hard workout, you may actually be blunting the training stimulus from all that hard work.

My contention is that athletes with limited training time benefit most from focusing on their primary sport. In other words, if you only have 6 hours a week to devote to training, you’re better off spending that time on your bike. There is one major reason for this: Dividing your limited time between strength training and cycling training often results in workloads that are insufficient to lead to significant progress in either arena.