Building Endurance Fitness

Dec 09, 2020

In working with our athletes, we design workouts that will address building fitness holistically.  Our goal is to increase aerobic threshold, lactate threshold, and VO2 max (AKA aerobic capacity).  If you are a coached athlete, you won’t necessarily need to know how to build fitness in a variety of areas, as your coach will put together plans that address all areas.  However, if you are self-coached, you’ll need to understand the type of workouts needed to improve all areas and how to put together a plan that finds the right balance between improving and not over-fatiguing the body’s systems.

VO2 max

One area in which athletes gain fitness and performance is by improving aerobic capacity or VO2 max.  VO2 max refers to the maximum volume of oxygen the body can deliver to working muscles per minute.  It is measured in millimeters of oxygen consumed in one minute per kilogram of body weight (mL/kg/min).  There are some fitness clubs and medical clinics that perform VO2 max tests; however, many athletes (especially amateur athletes) don’t know their VO2 max.  Your current VO2 max reading is not what is significant.  What is significant is building activities into your training that, over time, will increase your VO2 max.

 Why is it important for an endurance athlete to increase VO2 max?  During exercise, before you reach VO2 max, the body utilizes aerobic metabolism.  That is, the body is primarily using oxygen to fuel the necessary breakdown of carbohydrate, amino acid, and fat to support the activity.  Once you reach the plateau, VO2 max, the body switches to anaerobic metabolism.  The muscles fatigue, as the body no longer has the capacity to provide needed oxygen to the muscles.  This anaerobic state is not sustainable, thus the only way to keep moving is to lessen the intensity of the activity.  So, as VO2 max increases, so does your ability to push greater intensities for longer periods of time.  The most efficient way to build VO2 max is through high intensity interval training. 

Examples of VO2 max workouts:

Since swimming is usually measured in laps instead of time, a quality interval workout looks completely different depending on the athlete.  An athlete who can swim 400 yards at 2 minutes 30 seconds per 100 yards, needs a completely different workout than an athlete who averages 1 minute 15 seconds per 100 yards.

 For the first athlete, part of a swim session may include:

  • 10 x 50 yards with 45 second rest or
  • 20 X 25 yards with a 30 second rest.

For the second athlete, part of the swim session may include:

  • 10 x 200 yards with 60 sec rest at 96% threshold (400 yard race pace) or
  • 6 x 200 yards with 30 seconds rest at 96% threshold or
  • 20 x 100 yards with 30 sec rest at 95% of 200-yard race pace.

For biking, as part of a ride, short intervals at 110% - 120% of FTP with equal recovery times work well.  Such as:

  • 5 x 3 minutes with 3-minute recovery
  • 5 x 5 minutes with 5-minute recovery.

We are the most careful with building workouts to increase VO2 max while running, as by far, running puts the most stress on our bodies in comparison to swimming and biking.

 Again, as in cycling, we like to base these speed intervals on TIME rather than distance.  Such as:

  • 3 x 4 minutes at mile race pace (or 10 to 15 seconds per mile faster than 5K race pace) with 4-minute recovery
  • 6 x 3 minutes at mile race pace (or 10 to 15 seconds per mile faster than 5K race pace) with 3-minute recovery.

For our athletes new to running, we don’t build in VO2 max training until we know the muscular and skeletal systems are prepared to handle the added load.  Then we may start with 30 second intervals, and slowly increase those interval lengths as fitness improves.

 Lactate Threshold

While VO2 max is a great measure of fitness, it does not paint a full picture.  Lactate threshold (sometimes referred to as anaerobic threshold) also comes into play if a fit athlete is to maximize performance.

Under load, muscles produce lactate.  For each athlete, there is a unique work intensity at which lactate begins to accumulate in the blood faster than it can be removed.  Have you ever had to stop and “toss your cookies” mid-workout?  This is likely due to a lactate build up in your system.  For most athletes, lactate threshold is reached somewhere between 50% and 80% of VO2 max.  Increasing lactate threshold requires both proper training and proper nutrition. 

Examples of Lactate Threshold workouts:

The workouts we have found to be most beneficial include 7 to 12-minute tempo efforts (varies based on each athlete) with a recovery time of around one-fourth the interval time.  So, a portion of a weekly run may contain something like this:

  • 4 x 8 minutes at ½ marathon effort with 2-minute recovery or
  • 3 x 12 minute at ½ marathon effort with 3-minute recovery. 

On the bike, a workout designed to improve lactate threshold may have a component such as:

  • 2 x 10 minutes at 96% of LT (HR, power, or RPE depending on athlete) plus
  • 15-minute easy spin plus 
  • 10 minute hard effort or


  • 2 to 5 x (3 to 5-minute hill climb repeats, coast to bottom, spin easy on flats 5 minutes) number depends on fitness level and difficulty of the climb.

For many of our swimmers, the primary focus of each swim will be proper technique for open water swimming, as our swimmers are all triathletes.  So, although an athlete may not know he/she is working to increase lactate threshold, here are some samples of what may be embedded in a swim set:

  • 2 x 50 at best time plus 7 seconds 30 second rest plux
  • 100 super easy plus 
  • 4 x 50 at best time plus 5 seconds 30 second rest plus
  • 100 super easy plus
  • 6 x 50 at best time plus 3 seconds 30 second rest plus
  • 100 super easy or


  • 4 Rounds of :
    • 4 x 50 at threshold with 30 second rest plus
    • 100 easy

Whether swimming, biking, or running, lactate threshold also improves through daily nutrition, pre-workout fueling, during workout fueling, and post workout fueling.  For questions about proper fueling and nutrition, check out some of our other articles which specifically address eating.

Aerobic Threshold

Finally, the majority of weekly workout sessions are designed to build endurance performance.  You may have heard the term “long slow distance” or aerobic threshold.  These workouts are necessary for a plethora of reasons.  The slower pace creates much less stress and fatigue on the skeletal and muscular systems; thus, these workouts can happen while recovering from lactate threshold or VO2 max workouts.  These also bolster the body's ability to utilize stored fat as fuel rather than glycogen.  The body stores much more fat fuel than glycogen fuel, and these lower intensity workouts are proven to be the most efficient way to teach the body to transition from stored glycogen to stored fat usage.  Even the most fit athletes have enough stored fat to fuel for days, while only able to store enough glycogen for around two hours.  These long slow efforts also help the body increase it’s production of red blood cells and capillaries, increasing oxygen flow to the muscles.  These lower intensity training sessions will be the backbone of all our training cycles for running and cycling.  These workouts occur naturally in swimming when the main focus in a swim set is honing open water form.


If you’d like us to work with you to maximize performance through customized training blocks and nutrition strategies, join our team.  We’d love to partner with you!


50% Complete

Two Step

Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.