Lactate Threshold Training
By Ken Mierke
Whenever an athlete exercises at any intensity, even walking, lactic acid (lactate) is constantly being produced. Fortunately, our bodies also constantly recycle lactate, actually burning it up for fuel. As intensity increases, lactate production also increases. Lactate threshold is the highest intensity at which an athlete recycles lactate as quickly as it is produced, so that lactate does not accumulate. Muscle and blood levels of lactate are moderately high at lactate threshold intensity, but do not increase over time.
Lactate threshold training, in the right doses at the right time, is important for almost every road cyclist, mountain biker, and triathlete. For many athletes training for a variety of different events, lactate threshold training has the best cost to benefit ratio of any type of training. This intensity is high enough to stimulate adaptations which dramatically increase speed-endurance, but because lactate is not accumulating, damage to the muscles and blood vessels is minimal and the recovery cost of the workout, if conducted properly, is modest.
Increasing lactate threshold is one key goal of training for athletes racing in events lasting from thirty minutes to five hours. Raising lactate threshold enables an athlete to race more effectively at intensities significantly below lactate threshold, near lactate threshold, and above lactate threshold.
Most athletes and coaches overestimate lactate threshold intensity. This creates a major problem, either limiting potential training volume at lactate threshold or inducing overtraining. Training one percent over lactate threshold, at an intensity at which lactate accumulates slowly, causes much greater damage and requires much greater recovery time than the same duration at lactate threshold. This intensity, for a twenty to thirty minute segment, does not feel that much harder. Lactate accumulates slowly, but continually. Five minutes into the segment, lactate levels in the muscles and in the blood will be only slightly higher, but later in a long set they may be dramatically higher. An athlete with a lactate threshold of 350 watts and blood lactate of 4.2 mmol/L may reach lactate levels 50% greater after a 20 minute segment at 370 watts.
For most well-trained athletes, lactate threshold intensity correlates well with about CP75 wattage or speed. Be careful using CP60 because lactate accumulates at this intensity and because athletes don't understand the cost of going one or two percent too hard and coaches don't always get perfect compliance with the programs they design. Always remember that what happens on the roads and trails is more important than what we write on the schedule.
I find that most athletes can absorb relatively high volumes of LT training when intensity is carefully controlled not to exceed LT. I have also found that almost every athlete, at LT intensity, feels that they are not going hard enough.
Muscle Fiber Recruitment
Every muscle in an athlete's body is composed of many thousands of muscle fibers. When the muscle contracts, each fiber either contracts with its full force capability, or remains relaxed. When I pick up a one pound dumbbell, very few fibers are required to contract, but those that do contract just as powerfully as when I pick up a seventy pound dumbbell.
After aerobic plateau, which requires several minutes at the beginning of each workout or each shift in intensity during a workout, the athlete's body will recruit muscle fibers according to the power or speed requirement of the activity. The slow twitch fibers, because of their great endurance, will be recruited first. At low intensity only a few ST fibers will be recruited and the rest of the ST fibers, all the FOG fibers and all the FT fibers remain relaxed. As intensity increases, some of the FOG fibers will be recruited and then finally the FT fibers. At lactate threshold intensity, the power or speed requires the athlete's body to recruit all of the FOG fibers, but not yet any of the FT fibers.
At LT intensity, the FOG fibers create a lot of lactate, but only at a rate at which the ST fibers can burn it up and use it for fuel. Sustaining this intensity trains the FOG fibers to work more aerobically so that they produce less acid and trains the ST fibers to burn more acid, both of which push the threshold to a higher wattage or speed.
LT training is the only effective endurance training for the FOG fibers. At lower intensities they are not recruited. At higher intensities, FT fibers are recruited causing lactate to accumulate. Sustaining the intensity for an extended duration uses resources unnecessarily demanding tremendous psychological motivation and dramatically delaying recovery.
Using LT Training
There are two basic formats for LT training, cruise intervals and tempo segments. Cruise intervals are four to six minute segments at lactate threshold with one or two minute recoveries. These are very effective for introducing higher intensity training during late base periods. The recovery cost of cruise intervals is relatively light and the damage of riding slightly above LT intensity not as great.
Relatively long tempo segments are the core of LT training. I generally give my athletes two intensity zones for LT training.
High zone 4 is right at to slightly below LT. The athlete will sustain heart rate approximately 0-4 beats below LT and will sustain wattage or speed within three to five percent of LT. I generally use twelve to twenty minute segments at this intensity to increase power or speed at LT.
Low zone 4 is somewhat below LT. The athlete will sustain hear rate approximately 5-8 beats below LT, with wattage or speed about five to seven percent below LT. At this intensity, most of the FOG fibers are still recruited, but there is a safety zone against lactate accumulation. I have athletes perform tempo segments of twenty minutes all the way up to an hour at this intensity. Training at this intensity increases the endurance of the FOG fibers, enabling the athlete to sustain LT wattage or speed longer. I believe that this is an incredibly efficient training intensity. The cost, in terms of recovery for tomorrow's workout as well as the psychological costs, are relatively low. Most athletes enjoy this training and, prescribing very long sets may increase compliance with intensity. If I'm doing a forty minute segment, it is not so tempting to want to blast.
Every athlete likes to think that they are more motivated than the rest. They will train harder, be more consistent and more disciplined. Coaches like to think the same about their clients. Remember though, no matter how passionate and motivated the client is, this is a finite resource. Budget it wisely. Correct use of LT training, generally a little on the conservative side, plays a big role in sustaining motivation.
Implementing LT Workouts
Educate your athletes about the value of maintaining appropriate intensity. Make sure they understand that they are not sustaining 171 to 177 beats per minute so that they can finish the forty minute segment, but because that intensity produces the best results. As Joe says, The least amount of work which will produce the desired results. Remember the tendency of the athlete to want to go as hard as possible for whatever the duration is.
High, steady power or speed production is the key factor in LT training. Long steady bike segments generally need to be conducted in flat to rolling terrain unless the athlete is fortunate enough to live where long, steady climbs are available. Encourage your athletes to push harder than they think they need to on descents. Many riders with new power-meters are shocked at how little wattage they produce when they feel like they are pedaling relatively hard on descents. At the same time, exceeding LT power on uphills is natural, but not beneficial.
Indoor trainers provide a fantastic venue for LT training, but athletes vary dramatically on the psychological cost of these workouts. Some love it. For others this can be a great way to make them hate their bikes. I generally will use cruise intervals on a trainer more than steady segments because I like to keep the athlete's mind moving while riding on a trainer.
Group rides (for road cyclists) are generally not the best venue for LT training. Group rides tend to deteriorate into informal races, and those workouts certainly have their place. Getting a road cyclist to do a single weekly LT workout by himself may be the second greatest contribution a coach can make to his training (recovery weeks are #1). This will depend on the group and the athlete. A very strong and very disciplined athlete may be able to pull this off on some rides, but be careful. The right rider can even do this in a training race, going to the front and pulling for a certain number of minutes, before sitting in the pack to the finish. Still, for most riders, doing these workouts by themselves or with one or two partners who will cooperate with the intent of the workout is a better bet.
Depending on location, mountain bike riding is generally not the best implementation of LT training. One of my clients agrees to drive a four hour round trip to a thirty minute off-road climb that he does weekly during his build periods. Staying off his road bike for these twelve workouts is worth forty-eight hours in his car. Lots of serious mountain bikers hate their road bikes, but in many regions, finding long, steady off-road climbs is impossible. Mountain bikers tend even more to be outdoors people and many hate indoor trainers even more than road bikes, so the idea of a trainer LT workout on their mountain bike isn't often appealing (though the threat of that may make the road bike less horrible!).
Improving lactate threshold speed and endurance are primary goals of preparing for races between thirty minutes and five hours in duration. The FOG fibers will produce a significant percentage of the athlete's power or speed at these distances, and lactate accumulation in the muscles is likely to be the factor that limits performance.
LT training is still one important piece in events that are shorter or longer. Even though training the FT fibers will be critical, the FOG fibers still play an important role in events under thirty minutes duration.
Even though the ST fibers produce a huge majority of the energy to race an ironman and the FOG fibers will not be recruited for sustained durations, LT training (especially very long segments at the lower end) maximizes glycogen storage and vascularity as well as increasing central adaptations such as stroke volume.
The reality is that most athletes, at some point in an ironman, exceed aerobic threshold intensity and recruit the FOG fibers for moderate durations. Athletes will likely recruit the FOG fibers on a particularly steep hill even if they are disciplined and pace appropriately, so we do want these fibers trained even though they are relaxed for much of the race's duration. While training the ST fibers at AeT intensity should always be the priority in preparation for ironman and longer races, LT training, on the conservative end, still has value.
Type of Race
LT training is highest priority for time-trials, road races mountain bike races, and triathlons which feature long segments with high, steady power output, but increasing LT will help with any type of race of significant duration.
AT CP6 intensity, the FOG fibers generally expend about 30% of the energy, so even for a road race with several brutal climbs that are likely to determine the outcome, a mountain bike race with repeated short climbs, a criterium, or a hilly triathlon, increasing LT is vital to optimal performance. I often tell your road cycling clients who are gung-ho about very high intensity training, I'd hate to see you win the field sprint for 17th! Even in events won with a 1300 watt sprint, a high LT enables the athlete to arrive at the finishing stretch in a position to be able to use that sprint and with legs that are still able to sprint strongly.
Include LT training in appropriate volumes at appropriate times of the season. Learn each athlete, because the volume of LT training that can be absorbed and adapted to varies dramatically. This type of training is not the end-all and the be-all of endurance training, but it is one very efficient means of stimulating adaptations that will make our athletes stronger without beating them up or interfering with other workouts.