This has been extracted from the Peak Performance web site, with only a few modifications.
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Fortunately, glycolysis usually proceeds normally, without your having to think about it, and it also tends to 'keep pace' with your exertions; the more intensely you exercise, the 'hotter' the glycolysis fires burn. One very important consequence of this is that if glucose is broken down to pyruvic acid at very high rates, pyruvic acid can begin to accumulate inside your muscle cells, and an enzyme called lactic dehydrogenase can promptly convert much of the pyruvic acid to lactic acid. Is this bad stuff? As an athlete, you're probably no stranger to the idea that lactic acid forms rather readily in your muscle cells, especially when you are exerting yourself quite strenuously. In fact, you probably believe that the 'burn' you feel in your leg muscles when you're running, cycling, or swimming very fast is caused by lactic acid - and that the soreness you experience the day after an especially tough workout is produced by the same 'troublesome' compound. You may also cling to the idea that lactic acid is a 'waste product' formed in your muscles during strenuous exercise, and that lactic acid appears in your muscles when you 'run out' of oxygen, or because you've gone into 'oxygen debt'. In short, you probably believe that lactic acid is really bad stuff! Well, it isn't! All of the above statements are untrue: lactic acid doesn't produce burning sensations, it does not induce soreness, and it's not a form of metabolic 'rubbish' which must be eliminated from your cells as quickly as possible. In addition, oxygen shortfalls are not required in order to make lactic acid appear in your muscles and blood.
The truth is that lactic acid is produced in your body all the time, around the clock, even when you're at rest, and its concentrations rise whenever you take in a carbohydrate-containing meal. Fortunately, we're not telling you all this to improve your chances of gaining a PhD in cell physiology: We're giving you the straight scoop because an understanding of how lactic acid actually functions in your body can improve your performances tremendously! You see, instead of being a dangerous compound which wreaks havoc inside muscle cells, lactic acid (or more accurately, lactate) is actually the key chemical your body uses to 'dispose of' dietary carbohydrate; without it, it would be very difficult to maintain normal blood-sugar levels or keep your liver and muscles stockpiled with carbohydrate. About 50 per cent of the lactate you produce during a very tough workout is actually used by your muscles to form glycogen; far from damaging your tissues or inducing soreness, this glycogen provides you with the energy you need to carry out subsequent quality workouts ('Disposal of Lactate during and after Strenuous Exercise in Humans,' Journal of Applied Physiology, vol. 61(1), pp. 338-343, 1986). During exercise, lactate is an irreplaceable source of energy for muscles and other tissues, so much so that enhancing your ability to 'process' lactate can improve your race times rather dramatically. If you're a typical runner, the 'lactate training techniques' outlined in this article should hasten your 10-K clockings by at least a minute.
As if that weren't enough, lactate also helps keep you from getting fat. To understand how that happens, let's pretend that you have just finished a high-carbohydrate meal. Much of the carbohydrate in that repast enters your bloodstream as glucose - and heads straight for your liver. Paradoxically enough, your liver refrains from picking up this train-load of glucose, preferring instead to let it 'slip away' to the rest of the body. Once the glucose eludes your liver, it goes to many places, including your muscles, which can - via glycolysis - quickly break down the glucose to lactate, releasing usable energy in the process. Much of the lactate produced by glycolysis can return to the blood, head back to the liver, and finally be used to boost concentrations of glycogen (a key 'storage' form of carbohydrate) in the liver. This somewhat circuitous process of glycogen formation means that blood levels of both glucose and lactate rise after you've had your high-carbo meal. However, lactate levels don't rise nearly as fast as glucose concentrations, primarily because lactate is rather rapidly removed from the blood once it appears, while glucose is taken away only sluggishly. By changing some of the absorbed glucose from your meal over to lactate, your body quickens the 'disposal' of blood carbohydrate, thus controlling the amount of insulin which pours into the blood from your pancreas (the higher the glucose level, the greater the insulin response). This limiting of insulin production helps to prevent wild upswings in fat formation (one of the 'bad' points about insulin is that it coaxes glucose into adipose cells, where it is converted into blubber).
Lactate is also the primary player in an important process which occurs in your body - and which may be called the 'lactate shuttle.' Described by George Brooks and his colleagues at the University of California-Berkeley, the lactate shuttle involves the following chain of events:
Knowledge of the lactate shuttle helps you understand how important lactate really is: its easy diffusibility prevents glycolysis from shutting down, and its 'high-octane' fuel status helps a variety of cells to satisfy their immediate energy requirements or else store energy for future use. An understanding of the lactate shuttle also helps you make sense of those curious Scandinavian studies which have shown that vigorous training carried out with only the right leg can also upgrade the fitness of the left leg - and even that vigorous leg exercise can improve the fitness of the arms! Sure, there's a cardiovascular effect going on in such research (a heart strengthened by exercise will do a better job of getting blood and oxygen to the whole body), but the other part of the story is that the non-working tissues learn how to process the lactate 'spilled' in their direction by the hard-working cells (from one leg to the other or from the legs to the arms). As the non-exercising 'lactate-recipient cells' get better at using lactate, they have more energy available to sustain activity when they are actually called upon to exercise.
The lactate shuttle also helps you comprehend that mysterious phenomenon called the lactate threshold, or LT. When you begin a fairly moderate workout, lactate levels in your blood initially rise, simply because glycolysis is working away to provide quite a bit of the energy you require. If there were plenty of oxygen around, the pyruvate formed from glycolysis could 'be broken down all the way' to carbon dioxide and water, releasing a lot of important energy in the process. However, because you've just started your workout and therefore the blood and oxygen flow to your muscles is still somewhat minimal (heart rate is just beginning to rise, and capillaries leading into the muscle are not yet in the full-open position), pyruvate will be converted to lactate, and lactate will pile up inside your leg-muscle cells and begin spilling out into the blood. If we measured your blood-lactate levels at this early stage of your workout, we might find surprisingly high concentrations of lactate, even though you were ambling along at a pretty modest pace. If you keep moving along at a temperate pace, your blood lactate will quickly simmer down, however. As heart rate increases and capillaries dilate, oxygen will pour into your muscle cells, lactate will be oxidized for energy, and the spill-over process will abate. Your blood-lactate levels will drop a bit and then hold steady, which simply means that the entry and exit rates of lactate into and out of the blood are equal. And lactate levels may hold steady, even as you gradually increase your exercise intensity. As long as you're not going too fast, eg, as long as enough oxygen is moving into your muscle cells to take care of the pyruvate produced by glycolysis and thus control the lactate spillage, your blood lactate will appear to be as calm as a small Scottish pond on a windless day.
It's only when you get up to a point (actually to a speed or exercise intensity) at which glycolysis is tearing along so fast that your leg muscles can't convert all the lactate being formed into carbon dioxide and water that the spilling process may accelerate - so much so that lactate levels in the blood may really begin to lift off. This point may be reached because not enough oxygen is getting into the cells to 'handle' all the lactate (pyruvate) being produced, or because there are not enough enzymes available to guide along the pyruvate-oxidation process, or even because your tissues are not very good at 'clearing' large amounts of lactate from the blood. Whatever the reason, the lactate-appearance rate in the blood may suddenly exceed the lactate-disappearance rate, and so blood-lactate levels begin to climb. You have gone above your lactate threshold!
To put it another way, your lactate threshold (LT) is the running, cycling, or swimming speed above which lactate begins to accumulate in your blood. As mentioned, in one sense, that sudden lactate pile-up is normal: Every single endurance athlete in the world has an LT; everyone eventually reaches an intensity at which lactate begins to burgeon in the blood. However, if your LT is reached at a somewhat low exercise intensity, it often means that the 'oxidative energy systems' in your muscles are not working very well. If they were performing at a high level, they would use oxygen to break lactate down to carbon dioxide and water, preventing lactate from pouring into the blood. If your LT occurs at an inchmeal pace, it may mean that you're not getting enough oxygen inside your muscle cells where it really matters, or that you don't have adequate concentrations of the enzymes necessary to oxidize pyruvate at high rates - or enough mitochondria in your muscle cells (mitochondria are the small grain-like structures which are the actual sites for the oxidation of pyruvate; without mitochondria, pyruvate simply can't release its energy to the cell). As mentioned, since blood lactate depends not only on lactate formation but also on how well your tissues can utilize lactate once it appears, a low LT can also mean that your muscles, heart, and other tissues are not very good at extracting lactate from the blood. In practical terms, you want to progressively move your LT to higher and higher running, cycling, or swimming speeds, because doing so will mean that your oxidative energy systems are improving and that your muscles are getting better at pulling lactate out of the blood and using it for energy. In effect, having a low LT is not bad in itself (the lactate won't hurt you) but is a symptom that all is not well with your muscles' 'machinery' for breaking down pyruvate, using oxygen, and/or processing lactate.
It's important to note that for many endurance athletes improving lactate threshold is the key to better performances. A variety of different scientific studies have shown that lactate threshold is the single best predictor of endurance performance - better even than that vaunted physiological variable - VO2max, aka maximal aerobic capacity ('Blood Lactate: Implications for Training and Sports Performance,' Sports Medicine, vol. 3, pp. 10-25, 1986, and also 'A Longitudinal Assessment of Anaerobic Threshold and Distance-Running Performance,' Medicine and Science in Sports and Exercise, vol. 16(3), pp. 278-282, 1984). There's also great news (and certainly great news should be very welcome now that you've waded through all this physiology): not only is LT the best predictor of performance, but it is also very responsive to training - much more responsive than VO2max. If you've been training for several years, VO2max may not move upward at all over the course of a single year of hard work, while LT might soar by up to 20 per cent!
Remember Marc Rogers - our St.-Louis-Marathon winner? You'll recall that he won the race not because of a big move in VO2max, which actually was static despite a very impressive training regime, but because of a huge lift-off in LT. Marc's 'machinery' for oxidizing pyruvate and processing lactate improved dramatically, lifting his LT from 78 to 90 per cent of VO2max in less than four months of training, so he was the one who took home the first-place trophy!
Why is LT so dynamic? 'The skeletal muscles can adapt rather suddenly and strikingly to training, producing major gains in LT,' says Marc, who is currently an exercise physiologist at the University of Maryland. 'In contrast, VO2max is a fairly stable cardiovascular variable in experienced endurance athletes. To understand that, bear in mind that VO2max is to a large degree dependent on the size of the left ventricle (the key heart chamber which pumps oxygenated blood out to the body), and the left ventricle just doesn't change very much in volume after you've been training for a number of years. That's why VO2max values may not rise at all - or may only increase by a couple of percent, even with a high volume and/or intensity of training. Meanwhile, LT can be expected to increase from 5 to 20 per cent - given the appropriate training stimulus.' And research agrees.
Marc's comments are well supported by scientific research. For example, when scientists at Georgia State University and the Emory University School of Medicine followed nine elite distance runners over a two and a-half year period during which the athletes prepared for the 1984 Summer Olympic Games in Los Angeles, they found that VO2max remained unchanged over the entire 30-month period, while LT advanced by an average of 6 per cent. The LT upswing corresponded with either improved PBs or higher competitive rankings for the runners involved in the study ('Physiological Changes in Elite Male Distance Runners,' The Physician and Sportsmedicine, vol. 14(1), pp. 152-171, 1986). Another exciting aspect of LT improvement is that it seems to be much less limited by the ageing process, compared with upswings in VO2max, economy and power ('Effects of Physical Training on Skeletal Muscle Metabolism and Ultrastructure in 70- to 75-Year-Old Men,' Acta Physiologica Scandinavica, vol. 109, pp. 149-156, 1980, and also 'Maintenance of the Adaptation of Skeletal Muscle Mitochondria to Exercise in Old Rats,' Medicine and Science in Sports and Exercise, vol. 15, pp. 243-251, 1983). To put it another way, as you get older, your best opportunity for improving your performances may come from LT-type training. That should not be a big shock. Remember that as you get older, maximal heart rate tends to decline by an average of one beat per year, and the strength and flexibility of the left ventricle also tend to diminish. These factors lower maximal cardiac output, a key component of VO2max. Meanwhile, those pesky little mitochondria which play a large role in boosting LT, and also the aerobic enzymes which give LT a kick-start, are not necessarily reduced by the ageing process ('The Ageing Muscle,' Clinical Physiology, vol. 3, pp. 209-218, 1983).
This ability of older athletes to make big advances in LT no doubt explains a fascinating piece of research carried out several years ago by researchers at Washington University in St. Louis. In that investigation, eight veteran athletes (average age 56) were compared with eight young runners (average age 25) who trained the same number of miles per week (41) and happened to have the same 10-K performance ability (mean 10-K finishing time for both groups was around 41:30). As it turned out, VO2max in the older competitors was almost 10-per cent lower, compared to the youngsters, and running economy was identical in the two groups. So why were the gray-haired harriers able to keep up with the rosy-cheeked saplings? If you're guessing LT, you're right! Both the old and young runners reached LT at a speed of about 230 metres per minute (about seven minutes per mile), so it was no surprise that both groups ran their 10Ks at a pace of around 6:42 per mile (LT and 10-K pace are predictably linked together). The higher VO2max values of the younger runners were irrelevant for predicting performances (those lofty VO2maxs should have foretold faster 10-K times for those young whippersnappers, but they didn't), because the LTs of the senior runners occurred at a higher percentage of VO2max! In fact, average LT for the vets settled in at 85 per cent of VO2max, while LT for the younger ones rested at only 79 per cent. As a result, the older runners were able to complete their 10Ks at about 90 per cent of VO2max, while the youngsters could only handle 81 per cent ('Lactate Threshold and Distance-Running Performance in Young and Older Endurance Athletes,' Journal of Applied Physiology, vol. 58(4), pp. 1281-1284, 1985).
However, it really doesn't matter if you're young or old: you can do the same thing. Giving your LT a hefty shove to a higher running, cycling, or swimming speed (eg, to a higher percentage of your VO2max) will allow you to keep pace with - or beat - individuals with higher maximal aerobic capacities and will also help you reach the PBs you have always dreamed about.
So how do you actually cure a sickly LT - or take a pretty good LT and make it sensational? Although athletes have traditionally believed that prolonged, moderate exercise represents the ultimate LT therapy, the truth is that fairly intense training is the best LT booster, because such workouts improve the heart's capacity to deliver oxygen and the muscles' ability to use oxygen once it's delivered, as well as the ability of the heart and muscles to 'clear' lactate from the blood. For example, in a study carried out at the University of North Carolina at Greensboro, runners who raised their average training intensity by completing two fartlek sessions and one interval workout per week boosted LT significantly in eight short weeks and shaved over a minute from average 10-K time. The fartlek work involved two- to five-minute bursts at 10-K pace; the intervals were completed at about 5-K speed ('Increased Training Intensity Effects on Plasma Lactate, Ventilatory Threshold, and Endurance,' Medicine and Science in Sports and Exercise, vol. 21(5), pp. 563-568, 1989).
The idea that intense workouts are best for boosting LT was even more strongly reinforced in research carried out at York University by Stephen Keith and Ira Jacobs ('Adaptations to Training at the Individual Anaerobic Threshold,' Medicine and Science in Sports and Exercise, vol. 23(4), Supplement, no. 197, 1991). In the York investigations, one group of athletes trained exactly at LT, a very popular way to attempt to heighten LT, for 30 minutes per workout. A second group divided their 30-minute workouts into four intervals, each of which lasted for seven and a-half minutes. Two of the intervals were completed at an intensity above LT, while the other two were carried out below LT. Each group of athletes worked out four times per week for a total of eight weeks.
In the second group, the 'below-LT' intensity (which was used for two of the four 7.5-minute intervals) corresponded to an intensity of about 60 to 73 per cent of VO2max, a very, very moderate intensity which is used by many runners during their long, slow runs and easy, shorter efforts - and which is unlikely to have much impact on LT. The 'above-LT' intensity (also used for two 7.5-minute intervals per workout) was set at about 30 per cent of the difference between lactate threshold and actual VO2max. 30 percent of the LT-VO2max difference would actually represent an intensity of up to 87 per cent of VO2max, or about 88 to 93 per cent of maximal heart rate. In terms of actual running velocity, it would correspond to a running speed which is almost exactly the same as 10-K pace (or perhaps a few ticks per mile slower). In contrast, actual LT intensity is more like 15-K to 10-mile race pace. An amazing result.
Which strategy was better for boosting LT - working at LT intensity or putting in the time above it? After eight weeks of workouts, both sets of athletes achieved similar increases in VO2max and LT. The actual gains in LT were absolutely tremendous, averaging 14 per cent in both groups! Advances in muscle-cell enzymes were also rather splendid - and nearly identical in the two groups. In an endurance test in which group members exercised for as long as possible at an intensity which corresponded to their pre-training LT, the above-LT trainees seemed to hold an edge, continuing for a total of 71 minutes, while the at-LT subjects could last for only 64 minutes. However, this difference was not statistically significant. At first glance, these results seem to suggest that there's not much advantage to be gained by sweating through above-LT workouts, but wait! If you've been following carefully, you probably noticed that the above-LT athletes really logged only 60 minutes of quality work per week (4 x 15 minutes), while the at-LT subjects put in 120 weekly minutes of quality exertion (4 x 30 minutes). To put it another way, the above-LT athletes achieved the same gains in LT and VO2max as the at-LT folks (and perhaps enjoyed a slight advantage in endurance) - with only HALF the total training time. It's reasonable to assume that had the above-LT athletes stepped up their volume of above-LT work a little bit, they would have outdistanced the mundane at-LT trainees.
Why does roaming above LT during training seem to be so effective at lifting lactate threshold? Research carried out with animals provides part of the answer. In investigations at the University of Missouri, several groups of rats hustled along on laboratory treadmills at a variety of different paces, which ranged from 15 to 37 metres per minute (43 to 100 minutes per mile). The faster (by rat standards) velocities produced a flood-tide of lactate in the rodents' bloodstreams, as expected, but the Missouri researchers also noticed something very interesting: high lactate levels were linked with glycogen depletion of the rats' 'fast-twitch' muscle fibres, not their 'slow-twitch' cells. In other words, fast-twitch fibres were primarily responsible for the huge upswing in blood lactate. Of course, fast-twitch fibres aren't heavily utilized during moderately paced running but play a larger and larger role as running speeds increase beyond LT pace. Compared to their slow-twitch brethren, these fast-twitch cells are ordinarily somewhat low on mitochondria and aerobic enzymes, so it makes sense that they would begin belching out lactate as they are called into play. If they are very, very poor at oxidizing pyruvate, massive amounts of lactic acid will be produced, and LT will be reached at a very mediocre pace. As they get better at breaking down pyruvate, less lactate will be produced and LT speed will of course increase, but there's only one way to stimulate the fast-twitchers to get better: it's to use them during training, specifically at fairly sustained, fast paces. To put it another way, fast-twitch muscle cells can be the 'culprits' behind a low LT, and the only way to upgrade their oxygen-processing machinery is to hammer away at them during training. You'll get more 'bang from your buck' with faster-paced training, compared to slower efforts; after all, your slow-twitch cells are usually pretty good at the oxygen game; it's your fast-twitchers which need to do their homework.
The advantages of faster training were also illustrated in research completed at the State University of New York at Syracuse. In this study, which was carried out over an eight-week period, the concentration of a mitochondrial enzyme called cytochrome c increased by about 1 per cent per minute of daily LT training, as long as training intensity was set at 85 to 100% of VO2max (eg, for 10 minutes of daily training within this intensity zone, subjects boosted cytochrome c by 10 per cent after eight weeks; with 27 minutes of daily training, cytochrome c advanced by 27 per cent). In contrast, working at only 70 to 75% of VO2max increased cytochrome c by only 2/3 per cent per minute of daily training (upswings in cytochrome c should be correlated with improvements in LT). In the Syracuse study, if one looked at fast-twitch muscle fibres only, the gains associated with faster training were even more impressive: 10 minutes of daily running at 100% VO2max roughly tripled cytochrome c concentrations, while running 27 minutes per day at 85% VO2max expanded cytochrome c by 80 per cent, and 90 daily minutes at 70% VO2max boosted cytochrome c by just 74 per cent ('Influence of Exercise Intensity and Duration on Biochemical Adaptations in Skeletal Muscle,' Journal of Applied Physiology, vol. 53(4), pp. 844-850, 1982).
Overall, the scientific research suggests that the range of intensities from about 5-K pace down to about 10-mile race pace is great for improving LT, with the faster paces within this zone being 'better' for raising LT when the improvement is plotted as a gain per minute of training. However, the advantage of the 'slower' paces within this zone is that they can be used for many more minutes of weekly training, sometimes overcoming their per minute disadvantage (for example, it is much easier to complete 40 minutes of training at one's 10-mile race pace during a week of training than it is to charge through 40 minutes at 5-K pace, and the risk of overtraining and injury is also lower). The 'slower' paces may also be used for very long intervals and for up to 30 minutes of continuous running, which helps athletes develop the ability to sustain quality speeds for longer periods of time. In contrast, shorter intervals may have a more productive intensity but they don't simulate race situations as well (few races feature recovery intervals). For cyclists and swimmers, the range of heart rates between 85 and 95 per cent of maximal appears to be optimal for heightening LT. As with runners, the higher end of this heart-rate zone is more productive for boosting LT when the improvement is plotted as a gain per minute of training. However, the lower heart rates can be used for many more minutes of weekly training.
Supporting the idea that the moderate end of the LT-raising zone can be great for spurring performance, research carried out at Charles University in Prague, Czechoslovakia, determined that runners improved their LTs and performances most dramatically when they augmented the amount of weekly running carried out at velocities which fell between 10-K and 10-mile race speeds (10-K velocity is about 2 to 3 per cent above LT pace, while 10-mile velocity is very close to actual LT speed, as mentioned). In this Czech research, a group of seven experienced runners reduced the amount of aerobic training they carried out (aerobic workouts were defined as those conducted at a pace slower than 10-mile race speed) from 80 to 72 per cent of all miles over a four-month period. Meanwhile, the quantity of LT training (defined as runs of five miles or less at a pace somewhere between 10-K and 10-mile race speeds) advanced from just 6 to 16 per cent of all miles (the remaining, basically unchanging volume of 12 to 14 per cent was always reserved for short, speedy intervals on the track at faster than 10-K pace). As a result of the increase in LT training, LT velocity improved by a full 10 per cent in four months, and 10-K race times sharpened by almost a half-minute - from 28:45 to 28:20 ('Ventilatory Threshold and Mechanical Efficiency in Endurance Runners,' European Journal of Applied Physiology, vol. 58, pp. 693-698, 1989).
It is important to note that the more temperate end of the 'LT training zone' (eg, paces which are closer to 10-mile than 5-K velocity or heart rates which are nearer 85 per cent of max rather than 95 per cent) seems to work best when these 'cooler' paces are sustained in a continuous manner for periods of 20 minutes or more. An example of this is the classic study carried out at the famed Karolinska Institute in Stockholm, Sweden, many years ago. In this research, Swedish runners added just one thing to their usual training - a weekly 20-minute run completed at a pace which was about 10 to 12 seconds slower per mile than 10-K race speeds, which happens to be just about 10-mile race speed, or the bottom end of the LT zone. After a total of 14 weeks, the Swedes' LTs improved by 4 per cent, and 10-K times were trimmed by over a minute ('Changes in Onset of Blood Lactate Accumulation (OBLA) and Muscle Enzymes after Training at OBLA,' European Journal of Applied Physiology, vol. 49, pp. 45-57, 1982). In addition to being a good duration for a long, LT-boosting interval, 20 minutes may just be a threshold for the amount of weekly LT-type work needed to heighten LT significantly. Research at the University of Ulm in Germany determined that investing 20 minutes or more per week in LT training can lead to large LT lift-offs, while completing less than 20 minutes of weekly LT work is linked with mediocre thresholds.
© Owen Anderson (and Roger Caffin) 1/3/2002