When you swim at a steady pace, your body relies on its aerobic system to produce energy. Eventually the energy from that system is depleted, and you switch to the anaerobic system. This crossover of energy systems is known as the anaerobic threshold. Energy from the anaerobic system is limited, and you will quickly fatigue. Thus, anaerobic threshold is a quality indicator of how aerobically fit you are.
Lactate Threshold
When you reach your anaerobic threshold in swimming, you will also experience an increase in levels of blood lactate. At a steady swimming pace, lactate is removed at the same rate it is produced. When your body switches to the anaerobic system, lactate is no longer removed at the same rate it is produced. Therefore, one way to measure your anaerobic threshold in swimming is by conducting a lactate threshold test. Lactate threshold is defined as the level of exercise in which lactic acid rises above baseline levels.
Step Test
For swimming, you can use the 7x200 m step test to measure your anaerobic threshold. You will need a pace clock, stopwatch, heart rate monitor and equipment for blood lactate testing. Each 200 is swum at a steady pace using your preferred stroke. Your target time will depend on your level of swimming. Take your personal best time for that event and add 35 seconds for the first step. Subtract five seconds for each of the subsequent steps. Swim the seventh step at maximal effort.
Measurements
Between each step, take five minutes to rest. Immediately at the rest period, record your heart rate. One minute into the rest period, measure blood lactate levels. Additionally, record your split times, total times and stroke rate.
Determining Anaerobic Threshold
Once you have completed the step test, graph your heart rate over velocity and your lactate over your velocity. Where your lactate levels rise above 4 or noticeably spike is your anaerobic threshold. Take note of where your heart rate is as well. With conditioning, your anaerobic threshold will improve so that you can swim at a higher intensity for a longer period of time.
References
- "Physiology of Sport and Exercise"; Jack H. Wilmore; 2008
- "Journal of Exercise Physiology Online"; Comparison of Three Different Step Protocols in Elite Swimming; Zinner, et al.; February 2011
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