Crucible Fitness | Triathlon Training Articles

Critical Speed
By Rich Strauss

The first alternative method of determining training intensity is Critical Speed. This method is especially applicable in swimming and running, and to cycling on a trainer.

Velocity is a measure of the work produced by a runner, swimmer, or cyclist. In order for a runner to move the mass of his body over a distance of 400 meters in 82 seconds, he must produce a very specific amount of work. The same is true of a swimmer that swims 100 yards in 75 seconds. However this use of velocity to measure work produced is only applicable if the effects of wind, grade, and current are minimized or eliminated. This means that Critical Speed workouts are best performed on a track, treadmill, bike trainer, or in the pool.

Critical Speed is defined as your maximum average velocity maintained for a specific period of time. For example, a swimmer performs a 1 minute time trial and swims 75 yards. Dividing 75 yards by 60 seconds gives us an average velocity of 1.25 yds/sec. Our swimmer next does a 6 minute time trial, and swims 425 yards. 425/360 = 1.18 yards per second. This process is repeated for time trials of 12 and 30 minutes in length.We put this data into a table and determine his Critical Speed for each time trial length, and from it determine his Critical Speed per 100 yard pace:

CS Levels and the Systems They Train

Ideally we would continue this time trial process for 60 and 90 minute durations, for swimming, 60, 90, 180 minutes for cycling and running. But if we plot this data on a graph, we see that as the pace becomes more aerobic, the curve begins to flatten out. For this reason we can extend a line from the slope at CS 30 to determine paces for CS 60/90/180. What do we know from this? At his current level of fitness, he was able to maintain a specific workload for 6 minutes. This level of fitness yielded a velocity of 1.18 yards per second for 6 minutes. As our swimmer becomes more and more fit, he will be able to maintain a higher work load, and thus velocity, for longer periods of time. His CS at each time trial length will increase.

Training at specific CS levels induce certain training responses in our body, similar to how training at specific heart rate zones improves certain exercise systems. The following table lists the CS levels and the systems that each train:

CS 0.2

Workout Type: Power
System Challenged: Anaerobic
Physiological Adaptations: Fast twitch muscle development, increased muscle fiber development, increased neurological recruitment

CS 1

Workout Type: Anaerobic Endurance Speed
System Challenged: Anaerobic
Physiological Adaptations: Improved lactate clearance, increased blood buffering of lactate, improved muscular development, improved economy

CS 6

Workout Type: Anaerobic Endurance Speed
System Challenged: Anaerobic Capacity
Physiological Adaptations: Increase heart stroke volume, increased glycolytic enzymes, increased blood volume, improved economy

CS 12

Workout Type: Anaerobic Endurance Force
System Challenged: Anaerobic Capacity
Physiological Adaptations: Improved stamina, increased heart stroke volume, slow twitch muscle development, increased oxidative/glycolytic enzymes, increased blood volume

CS 30

Workout Type: Muscular Endurance Force
System Challenged: Aerobic-anaerobic
Physiological Adaptations: Elevated lactate threshold, slow twitch muscle development, increased oxidative/glycolytic enzymes, improved economy

CS 60

Workout Type: Muscular Endurance
System Challenged: Aerobic-anaerobic
Physiological Adaptations: Improved stamina, elevated lactate threshold, increased oxidative/glycolytic enzymes

CS 90

Workout Type: Aerobic Endurance
System Challenged: Aerobic
Physiological Adaptations: Improved endurance, elevated lactate threshold, slow twitch muscle development, increased oxidative/glycolytic enzymes, connective tissue development

CS 180

Workout Type: Aerobic Endurance
System Challenged: Aerobic
Physiological Adaptations: Improved cardiovascular endurance, slow twitch muscle development, increased oxidative enzymes, connective tissue development, increased muscle fuel storage, increased capillarization

CS 180

Workout Type: Aerobic Endurance
System Challenged: Aerobic
Physiological Adaptations: Removal of metabolic waste, regeneration

* Adapted from the Power Tap Training Manual, by Joe Friel

Testing Critical Speed

How: After warming up, perform a maximum effort time trial for the prescribed time. Because CS is a measurement of the average speed for the length of the time trial, pacing is critical. You don't want to go out too fast, only to blow up, or go out too slow and have something left over at the end. Because you are time trialing for a specific time, you will also need to determine how much of an extra lap you did on the track or in the pool. For instance, 435 yards in the pool for CS6. To determine CS on a bike, you will need to use a wind or other trainer that increases resistance as you go faster. Because the effects of wind are magnified on a bike if the testing is performed on the road, it will be harder to duplicate conditions from test to test.

When: During a recovery week, before beginning your next training phase. You want to repeat testing conditions from test to test. Potential variables include nutrition, hydration, recovery, sleep, time of day, temperature, etc.

What do you do with CS paces?

After determining your CS values in your recovery week, you then use these paces to determine training intensities for the following training phase.

Example: At the end of Base 2, you perform Critical Speed testing on an indoor trainer and determine a bike CS 60 of 22.4 mph. When you planned your training at the beginning of the year, you also determined that one of your weaknesses was Muscular Endurance, and that you were going to hit this hard in Base 3. You use the CS 60 value to determine your goal pace for your bike Break Through workout in Base 3, Week 1: 2 x 20 minutes at CS 60, or an average speed of 22.4 mph. This workout must be performed on the same wind trainer as the test.

What makes Critical Speed a very valuable tool is that it improves as your fitness improves. This way you are ensured that you are working at the proper intensity, given your current level of fitness. When controlled for wind, grade, and current, Critical Speed is a clear window into training intensity, unclouded by the other variables that affect heart rate.

We all know that the body is a wonderfully adaptive machine. Introduce a training stress, and then allow time for the body to recover. During this recovery period the body adapts to better cope with this increased stress. Repeat the stress and the body now performs more efficiently than during its first exposure. The cardiovascular system becomes more efficient in its job of delivering oxygen to working muscles. The neuromuscular system becomes more coordinated, producing more efficient and economical movement at increased paces.

But if you do not expose your body to higher and higher levels of training stress (intensity), it will not continue to adapt. Simply stated, if you train slow you will be very good at......racing slow.

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