Cardio workouts are divided into two categories based on what fuel the muscle uses: Aerobic and Anaerobic.

– Aerobic: Your muscles use oxygen to drive glucose breakdown.

– Anaerobic: Your muscles aren’t receiving enough oxygen to drive glucose breakdown and must turn to internal energy sources for fuel, which produces lactate.

Swimming is inherently more Anaerobic than other cardio exercises like running or cycling. However, that doesn’t mean we should exclusively engage in Aerobic workouts while swimming. Anaerobic training should have a place in every swimmer’s regimen.

Anaerobic workouts are designed to increase your body’s lactate tolerance and build stamina. Anaerobic swimming consists of shorter, fast-paced sets with longer rest periods designed to push you to 90-95% of your max heart rate.

By incorporating Anaerobic swims into your training, you will ultimately become a stronger, faster swimmer.

Anaerobic Vs. Aerobic Swimming Workouts

Anaerobic and Aerobic workouts are on opposite ends of the spectrum. While Anaerobic swims focus on short, fast sets with longer rest, Aerobic swimming focuses on longer distances at a slower pace.

Aerobic workouts involve swimming longer distances, whether that’s multiple sets of 200s in the pool or a few miles in open water.

They are characterized by low to moderate levels of RPE for an extended duration.

Aerobic swimming primarily aims to push your body’s cardiovascular system to carry more oxygen and strengthen your heart, the same as long-distance running or cycling.

Meanwhile, Anaerobic swims are short but incredibly intense, designed to activate your fast twitch muscles to develop explosiveness.

However, even though these two forms of swimming seem wildly different, they have a significant overlap. Even though Aerobic workouts primarily involve the use of oxygen to break down glucose, lactate is still produced in small amounts.

By engaging in consistent Anaerobic swims, you can improve your body’s ability to break down the lactate during your Aerobic swims and prevent your muscles from tiring as quickly.

The casual swimmer’s workout composition should highly favor Aerobic swims and only involve one or two weekly Anaerobic swims.

Benefits of Anaerobic Swimming

Whereas Aerobic swimming focuses on improving the amount of oxygen you can carry in the bloodstream, Anaerobic swimming focuses on improving your ability to function with lactate in your muscles and blood.

When training, your muscles may reach a point called the lactate threshold. When this happens, your muscles start to produce lactate, which builds in the bloodstream and creates the burn you feel while doing an intense workout. If you continue at that intensity, your muscles will eventually fail due to this buildup.

Anaerobic swims raise your lactate threshold and allow you to swim faster and longer before your body starts producing lactate.

Even once you reach your lactate threshold, consistent Anaerobic swims will train your body to process lactate quicker and turn it into energy more efficiently while increasing your muscle’s ability to continue functioning in the presence of lactate.

By repeatedly exposing your muscles to high lactate levels, you will develop more fast twitch muscle fibers, the part of the muscle responsible for short, explosive movements such as sprints.

In addition to improving your sprinting ability, training your muscles to function well in a high lactate environment also helps your Aerobic training.

Aerobic training also creates lactate, but at a much lower volume. Training your muscles to function more efficiently in the presence of lactate will allow you to build stamina and overall endurance.

Who is Anaerobic Swimming For?

Anaerobic swimming is for every swimmer who wants to improve and get faster and stronger, but it is especially beneficial for sprinters. Anaerobic swimming trains and strengthens fast twitch muscle fibers, the primary muscles used when swimming at higher speeds.

Every swimmer should consistently engage in some level of Anaerobic training. However, swimmers specializing in sprints should focus on anaerobic workouts.

Sprinting forces your muscles to burn more energy than they can produce using oxygen, causing them to switch from the more efficient Aerobic breakdown of glucose to the inefficient anaerobic process. The Anaerobic process results in a buildup of lactate that will eventually cause muscle failure if sustained for periods longer than a few minutes.

By engaging in consistent Anaerobic training, you can strengthen your fast twitch fibers and increase your lactate threshold, allowing you to swim faster for longer distances.

Both Anaerobic and Aerobic workouts have their place in a swimmer’s repertoire. Competitive swimmers, especially sprinters, will focus more on building their speed and incorporate more Anaerobic swims into their week.

Casual swimmers should only incorporate Anaerobic swims once or twice a week as a part of a well-rounded swimming regime.

Anaerobic Swimming Workout for Beginners (Example)

Some example sets of Anaerobic swims for beginners are listed below. The goal is to push yourself to swim as fast as you can in short bursts to target the Anaerobic fast twitch fibers, and then rest for a few minutes to allow your body to clear most of the lactate. 

Distance	Reps	Speed	Rest
25	12	90-100%	2-4 minutes
50	8	80-90%	3-5 minutes
100	4	80-90%	4-6 minutes

These sets should be done at about 80-90% of your RPE, which would ideally make your heart rate reach 90-95% of your maximum heart rate. They are designed to push your cardio ability to the very limit.

Anaerobic Swimming Workout for Intermediate (Example)

Below is a more challenging Anaerobic ladder workout. It should also be done at 80-90% of your RPE, operating towards the upper threshold of your maximum heart rate.

Distance	Rest
25	2 minutes
50	2.5 minutes
75	3 minutes
100	4 minutes
75	3 minutes
50	2.4 minutes
25	2 minutes

Remember, don’t skimp on the rests! They are vital periods of downtime to let your body recover from the exertion. If you feel like the sets are too easy with the entire rest period, you probably aren’t going fast enough.

How to Perform Anaerobic Swimming Effectively

To have an effective Anaerobic workout, you first need to determine what speed you should swim to gain maximum benefits. Luckily, determining your Anaerobic pace does not require expensive devices to measure your speed or exertion.

A good way to determine what level of exertion is right for your swims is to complete several sets of 25s, 50s, and 100s at what you think are easy, moderate, and hard levels on your RPE scale.

You can incorporate 200s or 400s in the mix if you are a more advanced swimmer.

Time yourself as you perform these sets to ensure that you are operating at the right levels. For instance, if you swim your ‘hard’ 50 yds at a 20-second per 25 yds pace, you should be able to swim your ‘hard’ 25 yds faster than 20 seconds.

This exercise will also give you a baseline to aim for in your Anaerobic sets.