Why you need tempo runs in your training plan...
The lactate threshold, or tempo run, has traditionally been hard to define, but here’s why it should be an essential part of your schedule.
Three decades ago, a team of exercise physiologists led by Bertil Sjodin of Sweden’s National Defence Research Institute put eight distance runners on treadmills. First, the scientists tested the runners’ blood at various paces, focusing on lactate, a chemical thought to correlate with racing performance. Then they asked the runners to do weekly 20-minute training runs at a pace they called vOBLA – the speed at which there was an ‘onset of blood lactate accumulation’ (OBLA) – what we call tempo runs.
After 14 weeks of such training, the runners saw their OBLA paces drop by four per cent, from 5:43 per mile to 5:29. This was one of several studies to highlight the tempo run as a critical element in training. But it also produced the misconception that there is one perfect pace at which these runs should be done – and that the best way to do them is to find that pace and stick to it for about three miles.
OBLA is also one of the easier performance parameters to change – much more responsive to training than VO2 max, for example. In fact, in Sjodin’s study, the runners’ VO2-max measurements didn’t budge.
Jack Daniels, legendary running coach and the author of Daniels’ Running Formula, defines ‘critical power’ more specifically, as about the pace you can hold in a one-hour race – for most of us it’s between 10K and 15K.
Coaches and runners say ‘lactate threshold pace’, ‘threshold pace’ or simply ‘tempo runs’. Breaking through the confusion begins with understanding the role of lactate in muscle metabolism. Lactate is a chemical with a bad reputation, associated with running too long at anaerobic paces. It has been blamed for everything from sore muscles to the dead-legs feeling you get at the end of fast-paced intervals. Lactate is simply a by-product of glucose metabolism and is produced any time you move a muscle. At low exercise levels, you use lactate nearly as quickly as it’s formed, and the amount that leaks from the muscles into the blood is minuscule. At higher levels – e.g. moderate-paced running – you produce it more quickly but also use it more quickly. More gets into the blood, but not much.
Research shows that when lactate climbs, the body uses the blood to ship some of it away from the hard-working muscles where it is produced to places where it can be used more effectively. One of these is the heart, another is the brain. But it also goes to the liver, which can use other energy sources such as fat to turn it back into glucose. Even some less-involved muscles, such as the arms, pull lactate out of the blood for fuel, in lieu of glucose.
This shuttling makes it possible for you to run faster, because glucose is the body’s high-octane fuel. We can generate energy much more rapidly with glucose than through lactate. So rather than being a sign that our leg muscles are drowning in performance-impeding lactate, the rise of lactate means the body is moving it to places where the power demands are lower, keeping the glucose for the running muscles.
That said, rising lactate and increasing fatigue go hand in hand, which means that even if lactate is no longer the evil we once thought it was, finding ways to train the body to use it more effectively – in essence, postponing the point at which blood lactate starts to rise – will also postpone the point of fatigue, with the hope of running further, faster. This, in fact, is what threshold training, in all of its confusing forms, is designed to do.
Efficiency training
Nobody knows why running at or near lactate threshold makes the body’s lactate processes more efficient. But training at this level can shift the entire lactate-increase curve to higher speeds.
Most coaches say the key is to run at what feels like the right effort level. ‘It would be hard to find definitive studies that said this is the one true way,’ says Halliwill. ‘What we can say is that when people train through a variety of approaches, whether it is lactate threshold or interval training at higher intensity, we see that critical pace – threshold – shift to higher intensities.’