Training at Different Energy Levels for Maximum Endurance

Over-training and a resulting injury or illness is something most of us will experience at some point in our swimming careers.  Even if you do not find yourself ill or injured, you may find yourself unusually fatigued and performing at a lower level than you are usually capable of.  So how can one prevent this from happening?  By planning workouts to work different energy levels, you can maximize the benefits to your endurance while avoiding over-training.  In short, train smarter, not harder.


Energy levels are something that many of you may be at least mildly familiar with.  There are a lot of terms thrown around and they can become very confusing, but here is a basic outline of energy levels as adapted from Ernest W. Maglischo’s book, Swimming Fastest.

En-1: Basic

Basic endurance training involves swimming at a slow and steady pace for long distances.  At this level, the body uses more fat than glycogen for energy, and the athlete can perform for long periods without damaging muscle tissue. This is the energy level for active recovery. There are many ways to determine whether or not an athlete is performing in En-1, including perceived exertion (60-70% effort) and heart rate (30-60 beats below maximum).


En-2: Threshold

Threshold endurance training involves swimming at a speed that overloads the aerobic metabolism, but does not lead to the buildup of lactic acid in the muscles.  En-2 is the optimum level for building endurance, as it develops the capacity of both fast-twitch and slow-twitch muscle fibers and VO2 Max.  However, En-2 relies more heavily on muscle glycogen for energy, which requires 24-36 hours to replace.  Threshold pace is equivalent to a perceived effort of 75-80% and a heart rate of 10-20 beats below maximum.


En-3: Overload:

Overload Endurance training involves swimming at maximal speeds, allowing the buildup of lactic acid in the muscles.  En-3 is best for training fast-twitch muscles and improves the body’s ability to remove lactic acid from the muscle.  En-3 level training causes muscle damage and should only be done 1-2 times per week, with plenty of allowance for recovery in between.  Overload pace results in a perceived effort of 90-100% and maximum heart rate levels.


Knowing the three levels and understanding the importance of using En-1, EN-2 and EN-3 during training puts a whole new perspective on the traditional “no pain, no gain” philosophy.  Use your AquaPulse to monitor your heart rate and stay in the designated energy level. Keep your competitive spirit in check to insure you don’t find yourself exhausted or injured due to over-training.


-Mallory Mead
Open Water Marathon Swimmer
Indianapolis, Indiana