Now some of the masters rowers that read this, may be thinking, what has a Tour de France cyclists performance got to do with rowing? They are not they same sports, and rowing is way tougher. They are not the same sports, yet both have similar demands on the body to produce enormous amounts of power. For instance, full throttle for a rider of Pogačar’s ability for an hour on the bike, is around 415 watts for his 65 kgs. That’s 6.4 watts per kg for an hour. For an 85 kg master’s rower, that would be an output of 544 watts averaging 1:26.3 500m split. Got your attention?

This update includes extracts from Training Peaks interview with Dr Íñigo San Millan, PHD (2020)

Dr Íñigo San Millán, PHD is the head of trainers staff at the World Tour Team, UAE Emirates, training last years winner of the Tour de France,  Tadej Pogačar. He is also a professor at the University of Colorado School of Medicine where he does clinical and research work in cellular metabolism, especially in diabetes, cardiometabolic disease and cancer. Dr San Millán focusing the development of his athletes using heart rate and power to guide training, yet it’s heart rate that he focuses on as the leading indicator to guide the training and the performance of champions.

Now some coaches, and rowers argue that training on the Concept2 by power (watts), or on the bike or in the boat with a power metre, is more precise and provides more immediate feedback to changes in effort. That’s true, but treating it as a replacement for heart rate assumes it measures the same aspects of training. According to Dr. San Millán, those that chose this approach, may be overlooking a key element.

“With watts, we’re just looking at the end product, which is mechanical energy, but we might be missing what happens at the chemical or metabolic level.”

Put another way, power meters measure what’s happening with the erg, gate or bike. But heart rate measures the individual. Ultimately it’s the individual that needs to be trained to produce the energy. While power indicates your power output, heart rate tells the metabolic cost of those watts.

Almost everyone training with a goal and a purpose has some form of structured training which is based on different training zones, intensities and workouts spread through a week or a training block, something that could also be called microcycle and macrocycle. While training in all zones is needed, zone 2 training should be one of the most important parts of any training program. Unfortunately, many novice or young athletes barely train or are prescribed zone 2 training and therefore don’t develop a good “base”, thinking that the only way to get faster is by always training fast. By doing this they won’t improve nearly as much as if they trained zone 2 in large amounts.

For the past 18 years working with professional and elite endurance athletes like cyclists, runners, triathletes, swimmers and rowers, Dr San Millán has been able to see that zone 2 training is absolutely essential to improve performance. By quantifying their training I have seen that their time dedicated for zone 2 training is somewhere between 60-75% of their entire training time. Very similar data across many different sports has been described by coaches worldwide as well as in the scientific literature.

The purpose of each training zone is to elicit specific physiological and metabolic adaptations in order to improve performance. It is important to know what physiological and metabolic adaptations occur while at different intensities and how they can be improved in training. To know this, we first need to have some understanding of basic bioenergetics and muscle metabolism.

Basic Exercise Bioenergetics

The capacity of an athlete to exercise ultimately depends on the ability to transform chemical energy into mechanical energy. Skeletal muscle needs to synthesize Adenosine Triphosphate, or ATP, for muscle contraction. ATP is a nucleotide responsible for the energy processes in human cells. It is often called the “molecular unit of currency” for the cells and needs to be synthesized constantly during exercise. ATP generation is achieved by two mechanisms- anaerobic and aerobic metabolism. Fats and carbohydrates (CHO) are the two substrates mainly used, with some contribution from protein. Fat it is stored primarily in the adipose tissue but it is also stored in skeletal muscle in small amounts. CHO are stored in the form of glycogen in skeletal muscle (about 80%) and in the liver (about 15%). The exercise intensity or metabolic and physiological stress as well as muscle fiber recruitment pattern will dictate the energy system and substrate that is activated, which will then correlate with different training zones.

The majority of exercise intensities generate ATP through aerobic metabolism, also called oxidative phosphorilation. Depending on the level of fitness of an individual, and up to 55-75% of VO2max intensity, ATP synthesis (energy) is generated from fat and carbohydrates, although CHO’s are used at small rates during low and moderate exercise intensities. At higher exercise intensities beyond 75% of VO2max, ATP generation needs to be faster in order to maintain muscle contractile demands. Fat cannot synthesize ATP fast enough so CHO utilization increases and starts being the predominant energy substrate as the rate of energy synthesis derived from CHO is faster than that from fat. CHO becomes the major energy substrate used by skeletal muscle at exercise intensities up to 100% of VO2max. Beyond this intensity, ATP cannot be generated by the aerobic glycolysis, so ATP needs to be generated through the anaerobic mechanism also called substrate phosphorilation. Essentially, going slowly lets your body use fats as fuel and as you increase the pace you increase the demand for CHO.

“The immense majority of activity that we do is aerobic. We tend to believe that any hard effort is anaerobic, and therefore the concept of anaerobic threshold. But actually, even what we call the anaerobic threshold is aerobic activity. The majority of the efforts that we do are in an aerobic environment except for when you do a sprint…or a one minute maximal.”

Iñigo San Millán, Ph.D

Types of Skeletal Muscle Fibers

Skeletal muscle is composed of 2 kinds of muscle fibers- Type I, also known as slow twitch, and Type II, or fast twitch. Fast twitch fibers are also divided in two subgroups called Type IIa and IIb. Muscle fiber contraction obeys a sequential recruitment pattern where Type I muscle fibers are the first ones to be recruited. As exercise intensity increases muscle contractile demands increase and Type I muscle fibers cannot sustain the necessary demand. Type IIa muscle fibers kick in and eventually as intensity keeps increasing Type IIb will finally be recruited. Simply put, slow twitch fibers are used at slower speeds and fast twitch at faster speeds. Each muscle fiber has different biochemical properties and thus different behaviors during exercise and competition. Type I muscle fibers have the highest mitochondrial density and capacity and therefore are very efficient at utilizing fat for energy purposes. Type IIa fibers have a lower mitochondrial density and a higher capacity to utilize glucose. Type IIb muscle fibers have a little mitochondrial density and a very high capacity to use glucose as well as ATP stored in these fibers for instant anaerobic energy. Therefore, each exercise intensity implies different metabolic responses and muscle fiber recruitment patterns which also corresponds to different training zones which are summarized below:

The Many Benefits of Zone 2 Training

In this training zone we stimulate Type 1 muscle fibers, therefore we stimulate mitochondrial growth and function which will improve the ability to utilize fat. This is key in athletic performance as by improving fat utilization we preserve glycogen utilization throughout the entire competition. Athletes can then use that glycogen at the end of the race when many competitions require a very high exercise intensity and therefore a lot of glucose utilization.

“One of the things that I’ve been focusing on these years is what I call the mitochondria function. This is key because this is where we oxidize fuels, where we burn the different fuels. We use our carbohydrates, fats and some protein as well, but the key is to utilize more fatty acids for energy purposes.”

Besides fat utilization, type I muscle fibers are also responsible for lactate clearance. Lactate is the byproduct of glucose utilization which is utilized in large amounts by fast twitch muscle fibers. Therefore, lactate is mainly produced in fast twitch muscle fibers which then, through a specific transporter called MCT-4, export lactate away from these fibers. However, lactate needs to be cleared or else it will accumulate. This is when Type I muscle fibers play the key role of lactate clearance. Type I muscle fibers contain a transporter called MCT-1 which are in charge of taking up lactate and transporting it to the mitochondria where it is reused as energy. Zone 2 training increases mitochondrial density as well as MCT-1 transporters. By training Zone 2 we will not only improve fat utilization and preserve glycogen but we will also increase lactate clearance capacity which is key for athletic performance.

As a takeaway, endurance athletes/Masters rowers, should never stop training in zone 2. The ideal training plan should include 3-4 days a week of zone 2 training in the first 2-3 months of pre-season training, followed by 2-3 days a week as the season gets closer and 2 days of maintenance once the season is in full blown. I like to use a portable lactate device to ensure my training intensities are dialled in. More about that in another article.

Dr Iñigo San Millán, Ph.D. 

Iñigo San Millán, Ph.D. is an Assistant Professor at the University of Colorado School of Medicine, where his areas of research, clinical work, and interests include exercise metabolism, nutrition, sports performance, overtraining, diabetes, cancer, and critical care.  He’s internationally renowned applied physiologist having worked for the past 20 years for many professional teams and elite athletes worldwide across multiple sports like running, football, soccer, basketball, rowing, triathlon, swimming, Olympics and cycling, including eight Pro Cycling Teams. Iñigo has also been a consultant in exercise physiology and sports medicine to international organizations like the US Olympic Committee and the International Cycling Union. He has been a pioneer in developing new methodologies for monitoring athletes at the metabolic and physiological level including a novel method to measure mitochondrial function and metabolic flexibility as well as the invention of the first method to measure skeletal muscle glycogen in a non-invasive way using high frequency ultrasound. Previously, Inigo was a competitive athlete and played soccer for 6 years for Real Madrid soccer academy team as well as raced as a professional cyclist for 2 years.