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In recent blogs and newsletters, I have extensively discussed 'within-session intensity regulation.' I believe that proper within-session intensity regulation is one of the most critical components of the training process. It's a topic I spend a lot of time contemplating, planning for, and researching.

But what exactly do I mean by 'within-session intensity regulation'? In this blog, I'll attempt to clarify this concept.

Context

Imagine you're training for an Ironman. You're currently in the midst of a four-week Specific Strength training block, focusing on (i) accumulating a substantial overall training volume and (ii) engaging in long, tempo runs on hilly terrain. Your training program emphasizes low-intensity sessions below the lactate threshold, allowing you to train extensively and frequently without inducing excessive fatigue (7, 8). The only sessions in your plan that exceed the lactate threshold are (i) a midweek trainer workout involving 8-minute...

On July 9th, 2023, Jan van Berkel, also known as "The Berklizer," triumphantly crossed the finish line at Ironman Switzerland, claiming 1st place. This race marked his final appearance as a professional triathlete, and as a coach, I can confidently say that witnessing this moment was one of the most emotional experiences I've ever had. From the exhilaration of his 4th race victory to the poignancy of concluding an almost 8-year coaching partnership, the range of emotions was remarkable. Coaches understand that, next to family, the professional athletes we guide hold a significant place in our daily lives. Jan had evolved into not just a athlete I work with professionally, but a close friend. The thought of the daily interactions coming to an end was a strange feeling, although true friendships are enduring.

My collaboration with Jan began during my tenure with Rowing New Zealand as the Head of Performance Physiology. The connection emerged after Eric Murray, a 2-time Olympic Gold...

As readers of our blogs will know, I am involved in research with colleagues at AUT in New Zealand on ‘durability’. We defined durability as the time of onset and magnitude of deterioration in physiological profiling characteristics – such as the ventilatory and lactate thresholds that mark the boundaries between intensity domains – over time during prolonged exercise (4). More simply, physiologically and perceptually, a 300 W effort when 20 min into a session is not the same as a 300 W effort when 200 min into a session. An athlete’s durability refers to how big the effect of those 200 min is.

We published a study last year that found an ~10% reduction in power output at the first ventilatory threshold (VT₁) following 150 min of moderate-intensity cycling (9). VT₁ is used as a marker of the transition between moderate and heavy intensity exercise. I use it as the upper boundary of “Zone 2”, and encourage my athletes to perform the bulk of...

In the triathlon and cycling communities, many of us have power meters on our bikes, or smart trainers at home. Power output data can be helpful in pacing efforts and tracking longer term progress. I myself programme many of my training sessions using power output – e.g. 4 x 40 min at 270 W for an Ironman workout – with the target number guided by the laboratory-based physiological profile of the athlete I am working with. For example, in the session above, the target power output is designed to be just above the first lactate threshold, in the so-called heavy intensity domain.

However, not all athletes have regular access to laboratory facilities for physiological profiling assessments and the determination of thresholds. For those athletes, power profiling represents an alternative, field-based method that can be used to provide anchor points in our training programming. Also, power profiling may be used to provide a still-elusive ‘durability’ metric. In...

A thought-provoking review on low carbohydrate diets and substrate oxidation rates was recently published in the journal Frontiers in Physiology (10). The author list includes a couple of the big names in low carbohydrate research, Tim Noakes and Jeff Volek. In this blog, I will summarise some of the key messages and takeaways from the review.

The traditional model of exercise and substrate oxidation

During prolonged, endurance exercise, we primarily use two fuels to support our metabolism and keep us moving. We have carbohydrates, which are stored as glycogen in muscles and in the liver, and we have fat, stored in fat cells and in muscle. The rate at which we use carbohydrates and fats to support metabolism changes with things like exercise intensity and duration (14, 17), heat stress (6), and recent diet (2, 16). As our carbohydrate stores are relatively modest, we can become carbohydrate-depleted, and fatigued as a result, after exercise of sufficiently demanding intensity and...

I recently made a post on Instagram that got a lot of attention and questions, and it was one that compared the percentage efficiency of carbohydrate (CHO) ingestion when was taking 120 g of CHO per hour. There were a lot of questions, and of course it’s hard to explain in enough detail via an Instagram story (see below).

So, as such, in this blog, I am going to have a look at the emerging literature suggesting it may be possible to ingest carbohydrate at rates as high as 120 grams per hour during exercise (that’s ~5-6 gels!). Carbohydrate ingestion during training and racing has a long history in exercise physiology, sports nutrition, and endurance sport. Despite decades of research investigating the optimum dose, type, and form of carbohydrate to support performance, research is still emerging that challenges our practices. So, let’s get into it.

Why carbohydrate during exercise?

We have often discussed how whilst the body’s fat energy stores are vast and...

In a story that has rocked the triathlon world, it has just been announced that American professional Collin Chartier tested positive for the banned substance erythropoietin – or EPO – in an out-of-competition test in February. Chartier, made miraculous strides up the ranks last year, winning the PTO US Open in Dallas.

There had been an immense amount of chatter in this space over the last day or so. And the bottom line is, doping in this manner (in addition to any manner) gives a huge competitive advantage. A clean sport is absolute paramount for fair competition, and our sport. So in this blog, I am going to do a bit of a deep dive into EPO, how it works, and the effect it has on performance – which is why it is often the drug of choice for those seeking to climb up the podium by means other than hard work and discipline in training. I have written a fair bit about EPO recently, after a couple of studies have been published demonstrating that ketone supplements...

There is increasing interest in the effect that ketones might have on the performance of athletes. We know that by consuming a diet very low in carbohydrates – less than 50 grams per day or so – we can enter ketosis or increase the circulating concentration of ketones in the blood. That’s why these diets are called ‘ketogenic’ (1, 8). In recent years, supplements have been developed that allow us to increase our circulating ketone concentrations independently of our habitual diet. These are the so-called ‘exogenous ketone supplements’ (9).

There are various types of exogenous ketone supplements, including ketone esters, ketone salts, and ketone precursors (that are converted into ketones in the body). Ketone salts combine ketones with sodium, potassium, calcium, or magnesium, and, predictably have the potential to provide a very high salt load. Ketone salts tend to provide a modest elevation in blood ketone, specifically D-βHB,...

Exogenous ketones have generated a lot of buzz in the endurance sports community over the last few years. Exogenous ketones are not to be confused with the ketones that circulate in the blood after adaptation to a very low carbohydrate, high fat, ketogenic diet; exogenous ketones are instead ingested in a supplement like a sports drink in much the same way that carbohydrates might be. There are a number of different types of exogenous ketones (6), with ketone monoesters seeing the most attention.

It was initially thought that, again like carbohydrates in sports drinks, taking on exogenous ketones during exercise might provide us with an alternative fuel source to help power long duration exercise and reduce use of our finite glycogen stores. There has been some indication that exogenous ketones do help us reduce glycogen use during exercise (2), although probably not via direct burning of the ketones to supply energy; the effect instead likely relates to some kind of signalling...

We have discussed at length in previous blogs how developing an advanced capacity to metabolise fat for fuel during exercise can be useful for long-distance triathletes. We’ve also published research on it; for example, one of our recent papers showed a relationship between an athlete’s peak fat oxidation rate (PFO) and performance in an endurance trial. The addition of PFO to traditional models of endurance – VO₂max, thresholds, and economy – improved the prediction of performance (16). Other labs have shown relationships between PFO and endurance, including Ironman performance (8). However, something I think is missing from the discussion is how having a robust ability to metabolise fat during training is helpful, specifically during high-volume days with multiple sessions. That will be the focus of this blog.

 Basics of carbohydrate metabolism

I feel like a bit of a broken record in this one, but during prolonged endurance exercise, we primarily use...