Volume and intensity are the two most important variables in triathlon training. Volume is how many hours/distance you cover across swim, bike and run and Intensity is how hard you do these things.
In triathlon training, the most effective way to gain fitness is by doing approximately 80% of your weekly volume at low intensity and 20% at a high intensity. We will define these variables a little later on. This 80/20 rule will give you a framework to plan and execute your training.
So your overall training load (a combination of the volume and intensity) will be pretty large at times. And as a result of this you may feel tired. Factoring in rest and/or easy days in-between harder sessions will help you gain fitness. If you train at a high intensity across multiple days and don’t allow enough recovery, you will quickly find that you are extremely fatigued, unable to hit numbers and often susceptible to picking up niggles or illnesses.
Triathlon being a multi sport event can get quite confusing about how to best split your time between the 3. A good rule for training distribution is splitting into 3 unequal parts depending on how long each section may take in a race. For example, if an Olympic distance triathlon takes 2 hours and is split into 1/4 on the swim, 1/2 on the bike and 1/4 on the run it makes the most sense to train in that distribution across the 3. Basically you would train 2x as long on the bike as you would for swim and run.
Volume
Volume is the combination of frequency and duration of your training. By adding up how many hours a week of training you do, you get volume. Across this weekly volume there will be varying degrees of intensity within the plan and its those parts that will help push up your fitness the most.
Let's say you have 12 hours a week you can train for swim, bike and run. You wouldn’t want to spend 4 hours doing each because each triathlon leg isn’t proportional. We would recommend you spend 6 hours on the bike and 3 hours each swim and run. This way you have a far more balanced programme that will address weakness and build volume across all 3 sports.
Intensity
Pace, heart rate, power and perceived effort are all ways we can monitor the intensity of sessions. Being able to assign a level of intensity to a workout with a numeric scale is a great tool to use across all 3 sports. As an example the 80% of your training should be done RPE 1-4 and your Intensity should be split between 5-8 (15%) and 9-10 (5%) depending on what sessions you have within your training programme.
Even though there are more ‘accurate’ ways to measure intensity like Heart Rate and Power, if you don't have access to those markers, using a RPE chart is still a very useful tool and one that the pros always come back to too!
Training for endurance sports is quite simple! Once you have your training zones dialled in, you will be able to monitor the length of time you stay in the appropriate zones. Following the 80/20 rule will ensure that you are sufficiently rested and recovered in order to really get the most out of your harder 20% sessions which in turn will lead to better race results!
Good luck!