Following up on the early post, on the The Power and Importance of Mitochondria, this article will zoom in a little more on HOW to develop your Mitochondria power houses. Adapted from multiple sources and inputs from experts in their field. The section on basic exercise Bioenergetics has been taken from Training Peaks online.
Almost everyone training for rowing, with a goal at the end of the season, has some form of structured training using either pace or heart rate zones, as a measure of training intensity. Whilst training in all zones is needed, zone 2 training, should be one of the most important parts of your training program for rowing.
Zone 2 heart rate intensity in a 5 zone model, is defined as training between 60 & 75% of your maximum heart rate.
Unfortunately, many novice or masters athletes barely train or are prescribed zone 2 training, and therefore don’t develop a good aerobic foundation, thinking that the only way to get faster, is by always training fast. By training this way, they won’t improve nearly as much as if they trained zone 2 in large amounts.
Working with successful masters rowers, focussed zone 2 training, is key to improve performance and to go fast. In reviewing their training, the fastest generally dedicate their time for zone 2 training around 90% of their entire training time and around 80% or 4 out of 5 training sessions are in zone 1 or 2. Very similar data across many different sports has been described by coaches worldwide as well as in the scientific literature by Dr Stephen Seiler PhD.
The purpose of each training zone, is to help you quantify and moderate your training intensity, and 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 energy requirements and the processing of energy by organisms, and muscle metabolism. The following is adapted from an article published in Training Peaks, author not identified.
Basic Exercise Requirements
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 (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.
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:
Training Zone Type/Energy Substrate Mainly Used/Type of Fiber
Benefits of Zone 2 Training
When you train in zone 2, you are stimulate Type 1 muscle fibers, therefore we stimulate mitochondrial growth and function which will improve the ability to utilise 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.
Besides fat utilisation, type I muscle fibers are also responsible for lactate clearance. Lactate is the by product of glucose utilisation which is used 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 masters rower, competing in an endurance sport. we should never stop training in zone 2. The ideal training plan should include a solid block of zone 2 training in the first 2-3 months of pre-season training, followed by blocks of training that included at least 80% of training sessions in zone 2, even in the racing season.
Key Take Away Points
- Training in zone 2 will help you to build a big aerobic foundation.
- Enhance ability to clear lactate
- Improve the bodies use of fat for fuel
- Support the foundation for the high intensity training required for racing
- Plan your season to include a good 8-week block of Aerobic foundation work in zone 2
- Train smart. Use a heart rate monitor, and dial in your training zones
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- Training Peaks – author not identified.
- Joe Friel (Dec 2013)