Endurance Training – Heart Rate Zones

Sport science has shown that as we exercise harder, the heart rate increases in direct proportion to the speed. Thus, due to the straight line relationship between training intensity (speed) and heart rate, we can use heart rates as a means of determining training intensity.

Once maximum heart rate has been determined, the following table can be used to establish heart rate training zones:

Zone Name Intensity
1 Recovery < 65% MHR
2 Aerobic 65-75% MHR
3 Extensive endurance 75-80% MHR
4 Intensive endurance 80-85% MHR
5 Anaerobic threshold 85-90% MHR
6 Maximum aerobic > 90% MHR
7 Speed Not applicable

These heart rate zones are scientifically based guidelines but they are only guidelines. Too many endurance athletes become slaves to a heart rate monitor or a heart rate that they saw in one of the many heart rate training books available. Many of these books assume each person has a maximum heart rate of 220-age, or that the zone 2 training zone can be determined by taking your age from 180. The only real way to determine your maximum heart rate is in a laboratory or using the all out or incremental tests discussed in detail in Chapter 6 of The Masters Athlete.

When using these heart rate zones and a heart rate monitor, it is also important to remember that heart rates will be higher when exercising in hot and / or humid conditions. This is due to the fact that when you train in the heat, you may dehydrate slightly through sweat loss. This lowers your blood volume that results in the heart having to pump more quickly and harder to get the same amount of blood and oxygen to the working muscles. Secondly, when training in the heat, blood is diverted to the skin to help off load the heat generated in the muscles. Again, the heart has to work harder to keep the amount of blood pumping to the muscles to give them the oxygen they require to maintain speed.

Research suggests that heart rates increase by 1.4% for each degree above 21 degrees Celsius. For example, at a constant pace, a heart rate of 140 at 21 degrees will become 160 at 31 degrees.

Bearing these considerations in mind, let us now discuss each of these training zones individually.

Heart Rate Zone 1

This is the recovery zone. The important factor here is that intensity is low and the duration generally short. This type of “training” is useful after competition, after hard training sessions such as those in levels 5, 6, or 7 or when the body tells you it’s time to lighten the load. Inexperienced aging endurance athletes or those with low endurance fitness levels generally recover more quickly from doing nothing, rather than zone 1 work.

Heart Rate Zone 2

This is the minimum intensity required to give an endurance training adaption. The beginner endurance athlete might start out at 65% of MHR but as fitness improves or the years accumulate, the intensity required to gain adaptations will increase to 70-75% of MHR. This is commonly called LSD (long, slow distance) or “conversation pace”. The adaptations that occur with this level of training include:

  • increased stroke volume (amount of blood pumped per heartbeat)
  • increased oxygen transport in the blood
  • increased blood volume
  • increased ability of the muscles to use oxygen
  • increased capillary (blood vessel) density within the trained muscles
  • improved use of fat as a fuel, thus teaching the muscles to conserve the limited carbohydrate (glycogen) supply

This type of training, together with level 3 extensive endurance training, forms the basis of endurance training and should be performed for a minimum of 30 minutes depending on the event being trained for. Obviously an Ironman (person!) triathlete would need to spend many more hours of level 2 training if they need to swim for 1-1.5 hours, ride for 5-8 hours, and then run a 42.2 km marathon. Aging endurance athletes should aim for a minimum frequency of three training sessions per week, with longer and more frequent sessions for the more competitive and experienced aging endurance athlete. This level of training should be emphasized during the preparation (pre-season) phase (see Chapter 6 of The Masters Athlete) of the training season but never forgotten during the other training phases.

Heart Rate Zone 3

This training is done at 75-80% of maximum heart rate for long periods (hence it is sometimes called extensive endurance). Examples are 10-30k runs, 40-120k rides, 5-15k rows or paddles, or 1500-3000m swims or longer sets of intervals. This type of training also takes place during the preparation phase of training and induces similar adaptations to those noted above for level 2 training.

Heart Rate Zone 4

This training is performed just below anaerobic threshold (80-85% of MHR) and because intensity is lifted, duration is reduced. Examples are 5-20k runs, 30-80k rides, 5-10k rows or paddles, or more intense intervals. Importantly, the intensity is just below “hurt but hold” anaerobic threshold intensity and is thus “strong but comfortable”. The adaptations that occur with this training include:

  • elevation of VO2max
  • elevation of anaerobic threshold
  • improvement in economy or efficiency

Like the previous zone, this type of training takes place during the preparation phase of training and also induces similar adaptations to those noted above for level 2 and 3 training.

Heart Rate Zone 5

It is difficult to understand how training at large volumes below planned race pace can possibly prepare you for endurance racing (zones 5-6), unless you are a marathoner or long distance triathlete who generally race at intensive endurance pace. It is therefore crucial for most endurance athletes to undertake some training at anaerobic threshold (85-90% of MHR). This type of training aims to expose the body to sustained exercise corresponding to the endurance athlete’s highest current steady state pace. In general, this intensity can be described as the “hurt but hold” intensity. The adaptations that take place with this type of training are:

  • elevation of VO2max
  • raising of the anaerobic threshold
  • increased removal of lactic acid
  • decreased production of lactic acid
  • increased tolerance of the pain of lactic acid being in the muscles
  • specific nervous system patterning of the muscle fibers needed during racing.

The intensity of training is elevated to 85-90% of maximum heart rate and can be done through continuous work of at least 20 minutes duration but no longer than 60-90 minutes (5-20k runs; 20-60k rides; 1500m swims) because after this time our muscles will run out of energy in the form of carbohydrate. Another form of zone 5 training is interval training with short recoveries that are half or less of the work time (10-15 x 100m swims; 15-20 x 1k cycles; 8-10 x 400m runs) (Figure below)

heart-rate

It is important with anaerobic threshold training intervals that the quality of the last interval should be as good as the quality of the first interval and the recovery relatively short compared to the interval duration. This type of training should be performed at the most twice per week, should be preceded by a good warm-up, followed by a good warm-down, and generally be preceded and followed by an easier (zones 1 / 2) day so that the quality of the workout can be good.

During anaerobic threshold training periods, recovery is critical and base-training intensities (zones 1-4) should not be forgotten. Recovery can also be enhanced by eating or drinking carbohydrate-rich foods since both levels 5 and 6 training mainly use muscle and liver carbohydrate as their energy source and supplies will be depleted after such training. The carbohydrates should have a high glycemic index (see Chapter 16 of The Masters Athlete) and be consumed ideally within the first 30 minutes after training but critically within the two hours after training.

Heart Rate Zone 6

Heart Rate Zone 6 or maximum aerobic training employs intervals with speeds that are greater than planned race pace but with long recoveries. The overall training volume during such a session is reduced, but the intensity is lifted, during this final pre-competition phase that lasts 4-6 weeks (see Chapter 6 of The Masters Athlete). Again, recovery (zones 1-2) training the days before and after these sessions is critical. Heart rate zones 2-5 training intensities should not be forgotten during this training phase. Examples of this type of zone 6 training are 3-8 minute (300-400m swims; 5k reps on the bike; 1k reps on the run track) repeats with 3-6 minute active (easy swim, spinning or jog) recoveries. Intensity is 90-100% of maximum heart rate for each interval but recovery intensity is down to 60-70% of maximum heart rate. Athletes should be well warmed up and build into the first 30 seconds of each interval. Repetitions depend on individual tolerances but 4-10 reps would be suggested depending on the individual athlete, their training age (years of training), fitness level, predisposition to injury, and whether you swim, bike or run which have an increasing “tear-down” factor. At the most, two sessions of zone 6 per week should be used with easy recovery work in between. Adaptations that take place with this type of training include:

  • increased tolerance to lactic acid
  • elevated VO2max
  • improved endurance speed

Heart Rate Zone 7

Speed training for the aging athlete is far more important than it is for the younger endurance athlete for a number of reasons. First, aging athletes tend to train with decreased intensities, suggesting that the fast twitch b fibers (the pure speed fibers found in large amounts in sprinters) are not activated at any time. If they are not activated, they decrease in size and possibly number – use it or lose it – and lead to decreased muscle size, thus muscle strength, and thus speed and power. Secondly, aging muscles that are used to contracting slowly as a result of slow training over longer distances, forget to turn over fast when in a race. Speed work (e.g. 3-20 second all out-efforts with long recoveries) done in short bursts once to twice a week depending on the training phase, can help the aging muscle and nerves to fire quickly. Thus, when faced with racing at a slower than sprint pace, the muscle scan cope. Two or more days of recovery at low intensity zones are needed to recover from these sessions as muscle damage is likely. Measuring heart rates during or at the end of all-out sprint work. However, they may be useful to see when you are recovered enough to sprint again.

For the aging endurance athlete, the vast majority of training should be in zones 2-4 with spikes of zones 5-7 depending upon the training phase.