Injuries are very common amongst runners, with research showing almost 80% of runners will experience injury at least once during a year. There has been significant attention given to running injuries, with runners, coaches and sports physiotherapists constantly seeking techniques and management for prevention. With a focus on load management and strength training, which are incredibly important, training intensity is a less common topic but one that can have a big impact on injury and performance.
Put simply, running intensity is how hard you are running, relative to how hard you are capable of running. Intensity is divided into three zones – low, moderate and high. Perhaps a lower intensity is something to consider for optimal performance for you.
Some Science Behind Running
We have 2 main energy systems:
● The aerobic system, using oxygen in a chemical reaction to create energy. There are no by-products, but it takes time to do this.
● The anaerobic system doesn’t use oxygen so it can make energy faster, but it has by-products like lactic acid that slow us down.
These 2 systems don’t work in isolation, but one will work more than the other depending on the intensity of the exercise.
If we are running at a low intensity and have enough time to use oxygen, the aerobic system will be used. As we increase intensity, the amount of energy provided by the anaerobic system increases until it nears 100% anaerobic. At this point we are producing too much lactic acid and have to slow down.
● Our aerobic threshold, or AeT is the point of 2mmol of lactate in the blood – this is when the anaerobic system is used more.
● Our anaerobic threshold, or AnT is the point of 4mmol of lactic acid in the blood – we are creating more than we can get rid of and can only sustain this intensity for a short time.
Benefits of Running Slower
To maximise your fitness gains, it is important to think about total volume, intensity and variability. When you become fitter and stronger, it feels good to run fast and it is tempting to keep increasing your pace. It makes you feel good, and it is an achievement, however it may do more harm than good in the long run. There are definitely benefits of running at a slower pace, including:
● Less risk of injury
With high speed, the demand on the muscles and tendons in our legs and feet increases. Some increase is good, as it improves the tolerance of the tissues – but only when it happens gradually. Too much too soon will overload the body and can easily result in injury.
● Maximising capacity of the aerobic energy system
The aerobic energy system fuels our body when performing an event for longer than 2 minutes. Therefore, it is critical for performance that we maximise aerobic capacity – the way to do this is to train below our aerobic threshold. If we run too fast, the energy demands rise, and we use more anaerobic energy systems which can result in Aerobic Deficiency Syndrome and poor performance. (More on this below).
● Maximising volume
It’s rewarding to measure your pace and distance, but the number of kilometres you run each week is not as important as the total duration. The cardiovascular system, (the heart and lungs), adapts to exercise based on the amount of time loading it, therefore the longer you spend doing that, the better. For example, running 100kms at 4:30 min/km works out to be 7.5 hours of training. If you slow your pace to 6 min/km, that will be 10 hours a week. Consider also, if you slow down, you will be less tired and can probably increase your total distance anyway.
Heart Rate Zones
Using your heart rate (HR) to determine intensity is the best way to plan training sessions and maximise their benefits. Once you have worked out your different HR zones and desired HR for a particular session, you run at a pace that matches that HR. Your pace will fluctuate depending on how you are feeling, which is really important as it means you are listening to your body’s needs.
There is a very simple HR zone system for personalising intensities to your unique metabolic response. Ideally, if you are at your physical best, aim to do 80% of your running in zones 1 and 2 and up to 20% intensity training in zones 3 and 4.
Zone 1:
● HR: AeT 20% – AeT 10%.
● Effort: Very easy to easy.
● Purpose: Aerobic conditioning.
● Method: Continuous from 30 minutes to several hours.
Zone 2:
● HR: AeT 10% – AeT.
● Effort: Easy to moderate.
● Purpose: Aerobic capacity, muscle economy.
● Method: Continuous for 30-90 minutes.
Zone 3:
● HR: AeT – AnT.
● Effort: Medium to hard, but not exhausting.
● Purpose: Aerobic capacity, anaerobic capacity, clearing lactic acid, muscle economy.
● Method: Continuous up to 60 minutes or interval reps of 10-20 minutes.
Zone 4:
● HR: AnT – max HR.
● Effort: Hard.
● Purpose: Max Anaerobic power, speed and strength endurance, muscle economy.
● Method: Intervals of 30 seconds to 8 minutes.
The AeT and AnT numbers are the key for determining your HR zones, and there are different options to test these numbers – Lab based lactate testing, HR drift test or lactate threshold test. Do some research into which may work best for you.
Keeping the 80%/20% rule in mind, you can map out your training schedule to include sessions at a variety of appropriate intensities. This allows you to train effectively and get good performance gains. Importantly, it will reduce your risk of injury as you have flexibility in pace and load.
If you do suffer a running injury, contact the team at Melbourne Sports Physiotherapy by phone or book an appointment online. Their goal is to get you moving pain free as soon as possible.