Fractional Utilization of VO2 Max (Lactate Threshold)

Fractional Utilization of VO2 Max (Lactate Threshold)

Lactate is a substance found in your body which plays a role in the metabolism to convert your energy stores into productive mechanical energy in your body.  Though different people have slightly more or less lactate, everyone can usually be found at rest around 1 mmol/L in the blood. When exercise begins, the amount of lactate in the blood starts to become effected. Though extremely gradual at first (perhaps unchanging for some), when the rate of carbohydrate utilization is elevated, the body cannot buffer out all the waste products creating higher levels of lactate accumulation in the blood. In other words, when an athlete is running slowly the majority of the energy which is being used is being taken care of in an efficient oxidative method which does not produce significant waste products to hinder performance. We have talked about this before in the “aerobic capacity” section earlier. When the running speed increases, the metabolism rate of that individual increases. Due to the need for high amounts of energy in this state, anaerobic glycolysis (rather than the more efficient oxidative phosphorylation) breaks down energy stores leaving significant waste products. When a high concentration of lactate is not transported in or out of cells quickly, accumulation of lactate occurs. A higher ph occurs as well due to static hydrogen ions which inhibit muscle contractions. This shows that the waste products, not the lactate alone, hinder the performance of the runner. This waste product, now referred to as lactic acid, as well as other factors (glycogen depletion, O2 flow, blood flow, etc) collectively, are the cause of muscular fatigue in runners.

Lactic acid often is felt significantly at the beginning of a training program because running form isn’t superior, MCTs 1 and 4’s expression is low, and Na/K pump expression is low. At the end of a training program often running form is more efficient, MCTs become lactate influx and effluxing engines and Na/K pumps in cells help resist against hydrogen ion build ups. In other words, your body both on the outside and inside becomes more efficient at dealing with lactic acid.

If someone were to ask me how to describe lactic acids effects in my own running I would tell them that from my perspective lactic acid fatigue is synonymous with pain management. Depending on the runner, different amounts of lactic acid in the body will force that individual to slow down. Phil Davies, a Sports Fitness Advisor, has said on his website, “It is thought that complete exhaustion occurs somewhere in the range of 20 – 25 mmol/L for most individuals although values greater than 30 mmol/L have been recorded.” Why are some people crippled at 20 mmols while others can maintain their form and confidence to continue? One of the more interesting things I have been exposed to lately is the idea of pain management. I just finished my last season of competitive collegiate cross country and I have looked back in hindsight at races that have been pivotal in my progression as a distance runner. I remember a 10k I ran during my first college track season where after running over 5 miles on a track (21 laps) I was able to accelerate my pace into 4:40 range with 4 laps to go. I felt fine during that lap, but WHAM it hit me. I could feel the accumulation of lactic acid shouting at me to slow down. I fought it the best I could and kept pushing. I felt as if I was maintaining that pace, but I realized that I was slowing down slightly. I threw in a final surge to kick off the last lap and finished that lap in 67 seconds completing the last 1600 in 4:59.

I remembered thinking after that race that when I decided to go as fast as I could there was something holding me back. What I believe now is that during these situations pain management becomes so important. Through years of workouts and race successes and failures I have learned that one of the reasons we train is to not only to train our body’s physiology but also our mental capacity to assure our body, during the race, that we have been through similar situations of pain and that this race or surge may hurt for a moment but will be ok.

There is a lactate threshold for all runners. Some runners can maintain a higher running speed, before lactate starts to accumulate, than others. It would be said that these individuals had a higher “lactate threshold” or LT. Lactate threshold is a very important factor for serious distance runners. When determining one’s lactate threshold a runner’s VO2Max is taken into account; hence the title to this section “Fractional Utilization of VO2 Max”. According to Tim Gibbons et al of the US Olympic Committee, “The [lactate turn-point] when expressed as a percentage of V02, is high in the endurance-trained athlete. In sedentary individuals, for example, the [lactate turn-point] may be at approximately 50-60% of VO2 max, whereas in endurance-trained athletes it typically occurs at around 75-90% of VO2 max.” When the word “turn-point” is said here, it is being identified as the point when running speed increases slightly but an athlete’s blood lactate readings jump immensely.

How can you increase your lactate threshold? Several different sources feel that a trusted way to increase a runner’s lactate threshold is to run “threshold runs” or runs right next to the point where lactate begins to accumulate in high amounts. If you ever get a chance to read Jack Daniel’s Running Formula, within that book there is a chart which can easily approximate the speed at which training runs should be accomplished, according to the athlete's VO2Max or current running ability. To get the best measurement to determine one’s lactate threshold a set of muscle biopsies or blood pricks would be needed. Due to the difficulty of this, a heart-rate training procedure can be used to replace these. Heart rate increase often is closely correlated with increases in blood lactate within the body. By calibrating a heart rate monitor for each specific athlete, workouts can be reviewed and can help determine an athlete’s threshold. By training at or slightly above one’s threshold level constantly, the body adapts and allows runners to push themselves into higher lactate threshold levels.

Genetics are often pointed to when lactate threshold is the topic. Several studies have shared their findings that increases in slow twitched muscle percentages allow for the highest possible LTs. Alternatively, a study produced by Adèle R. Weston et al. entitled African runners exhibit greater fatigue resistance, lower lactate accumulation, and higher oxidative enzyme activity, the researcher shared information which appears to question previous findings. The results highlighted findings that significantly more active oxidative enzyme activity (citrate synthase, and others) and longer time until fatigue was shown in African runners than in performance-matched Caucasian runners. Ironically the average type 1 muscle ratios were higher in the Caucasian runners who had an average of 67% versus African runners having only 49%. If the results found in this experiment are true, its implications cause one to consider the need of high slow muscle ratio for a distance runner.

Threshold training is important for distance runners. Though I have changed my philosophy of workouts many times since I begun running competitively, I naturally throw in threshold runs weekly because it makes me feel more powerful, more relaxed at “uncomfortable” paces and mentally stronger. I am only more and more convinced that there is a very close correlation between LT and pain management.

This last season of cross country I became curious about strength training in addition to my running. I would perform sessions of 30 minutes twice a week throughout most of the season. I did this mainly after reading the interesting studies about increased performance capability through changes to the neuromuscular adaptations. These exercises were almost entirely anaerobic in nature. I ended up doing very well at the end of the season and while I feel that my key running workouts were what help my body adapt the most, these strength training routines were excellent times where I could focus on pain management. In the weight room I am not sure if I was able to increase the strength of my running muscles in ways to help my body significantly, but I was able to help my brain/body take on high levels of pain. This made even the hardest workouts and races bearable.