• 16 JUN 14
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    Lactate is unique!

    Lactate is unique!

    I have previously described the three primary independent factors which dictate endurance cycling performance which are known to applied exercise physiologists….

     

    1. Gross cycling efficiency – the ability to use oxygen and convert fuel (carbs/fats/ protein etc) to energy in the muscles and is dictated by individual expression of specific metabolic enzymes which control the numerous biochemical pathways of energy production and oxidative phosphorylation in the mitochondria to ultimately produce ATP.

     

    2. Oxygen kinetics – yes this includes VO2max, but also sub-maximal oxygen delivery which is determined by the cardiac output (stroke volume multiplied heart rate), myoglobin content in the muscles and haemoglobin in blood, capillarisation of the muscles for oxygen diffusion.

     

    3. Lactate threshold – the work rate at which the muscles are not metabolically balanced and ‘fail’ rapidly, this is dictated by your neuromuscular firing pattern, ie the numbers of different muscle motor fibers needed to perform at different intensities and the composition which determines the synchronicity of those fibers. Eg, if you have too much anaerobic fast twitch muscle relative to aerobic muscle your endurance as indicated by threshold power will be sub-optimal. Also vice-versa, if you do not have enough anaerobic fast twitch muscle relative to aerobic muscle capacity, you will also be sub-optimal.

    For a long time now, many coaches/ scientists and researchers have focused on the aerobic system as the most important dependent element common to all-three factors which influence performance. However, while oxygen kinetics are still important sub-maximally…the major determinants of performance are in fact 1 & 3 from the above. The corollary (ie the natural conclusion from this) then would be that the anaerobic capacity is the most important determinant of cycling performance!! I can explain in terms of 1; as the point at which lactate accumulates dictates how efficiently your muscles are working by using fats and carbs aerobically. The environment caused by low oxygen conditions actually stimulates more aerobic enzymes to be expressed, hence increasing cycling efficiency. Lactate is an anerobic metabolite when oxygen isnt present (anoxia), a hypoxic metabolite when oxygen is available in sufficient quantities (dysoxia) and an aerobic metabolite in the presence of an adequate O2 supply and utilisation of glucose as a fuel.

     

    Lactate clamp and the fatigue myth…

     

    During exercise and muscle contractions , muscle and blood [lactate- and associated counter ion [H+] can rise to very high levels. Most researchers have argued that any detrimental effects of HLa on muscle and exercise performance are due to [H+] rather than [La-], which could depress muscle function through many biochemical interactions.

     

    • Reducing the force of cross-bridging in myofibrils.
    • Inhibiting maximal shortening velocity.
    • Inhibiting myofibrillar enzymes such as ATPase.
    • Inhibiting the production of ATP (glycolytic rate).
    • Reducing activation of crossbridge by Ca2+ binding to Troponin C.
    • Reducing Ca2+ release through inhibiting sarcoplasmic ATPase.

     

    Lactate clamp studies have been conducted to demonstrate the effects of a constant infusion of lactate on cyclists. Concentrations of lactate are introduced into the blood stream of participants of the study, which contain specific ratios of buffer ions to control the concentrations. Results showed that with exogenous (infusion) lactate, incorporation into glucose increased and the contribution of glycogenolysis to glucose production decreased. Lactate infusion was also ‘not’ associated with an increase in the sensation of fatigue. These observations are consistent with concept that lactate is a useful carbohydrate source that can spare blood glucose and liver glycogen in times of increased energy demand and use in other tissues.

    Supporting studies of this notion have been challenged by the potential role of inorganic phosphate (Pi) as a major cause of muscle fatigue. Pi increases during intense muscle contraction or exercise due to the breakdown of phosphocreatine (PCr).
    The concept of homeostasis in body fluid acid-base status is largely controlled by the stronger ion difference (SID).

    [SID] = ([Na+] + [K+] +[Ca2+) – ([Cl-] + [La-])

    although [La-] can be a significant component of SID acting to increase the [H+], it is definitely not the only factor involved in pH changes.

     

    A window into your physiology…

     

    So Lactate is not the direct cause of fatigue but is associated with failing muscles, and the profile of lactate concentrations for varying work rates is therefore physiologically unique to each of us.

     

    Hence measuring blood lactate, provides the best window into the functioning and synergy of the anaerobic capacity with the aerobic system. Basically, you just need the right amount of lactate to feed into your muscles when going uphill, sprinting and even flat riding speed. Although this has to be relative to your total capacity. Reducing the anaerobic capacity is also sometimes necessary, especially in newer cyclists.

     

    Lactate_metabolism_pathway

     

    This particular test is not designed to assess the strength of anaerobic system per se but one can see the anaerobic system at work through the lactate curve. When the pace or effort level reaches a certain point the lactate rises quickly. This is a direct indication that the anaerobic system is being used more and more.

    The graded ramp protocol is mainly used to measure aerobic capacity, but it also provides an estimate of the lactate threshold or maximal lactate steady state. So at every point lactate is telling you something about your conditioning level of both energy systems.

     

    • it shows where the threshold is; how fast or powerful you can maintain effort without lactate accumulating.
    • it gives an indication of the strength of the anaerobic system at high work rates.
    • it is a good estimate of the strength of the aerobic system.

     

    Pro-teams have their blood lactates checked by the team physiologist very regularly indeed during training, showing just how important and influential this marker can be. Some people can ride longer than an hour and some not so long, so the individual intensity varies considerably and hence so do the parameters. A properly conducted lactate profile performed at strategic points in your annual training will provide invaluable information to your performance progression, and let you understand the effectiveness of your training.

     

    Neither heart-rate or power provides this level of  information alone. This is why neither of these measures are a replacement for lactate. It would be best if it were possible to measure the lactate in the muscle but this is a highly complex procedure. Blood lactate is an alternative that has been shown to correlate well with muscle lactate.

     

    Lactate curves and anaerobic capacity information lets the coach understand each athletes body and how it responds to training and find each athletes best training practices. It is not a black box that is being trained but two energy systems, of which lactate is a window into both of them.

     

    Specific conditioning….

     

    The ability of the muscles to contract quickly for a peak performance during an athletic event requires that the energy systems providing energy be fine-tuned. They need to be balanced properly so the athlete can generate the highest amount of energy per unit of time during a race of a specific length. Proper training is what accomplishes this fine-tuning or optimal balance. Lactate testing lets the coach or physiologist know if the balance has been achieved, or how each energy system must be trained further in order to optimise the balance further.

     

    The anaerobic system is difficult to measure yet the most important one to measure. The main reason why nearly all sports scientists ignore the anaerobic system is that they say that it does not provide much of the energy for long events. But this attitude misses one of the key aspects of the anaerobic system, that the strength of the anaerobic system has a major impact on how much aerobic energy can be utilised, and that is critical to how well the athlete performs. It is not the amount of the anaerobic energy produced that is important but the controlling nature of the anaerobic system on total energy production that is important.  Specifically, if the anaerobic system is inappropriately strong, it gets in the way, and will depress performance in long competitions. So we repeat; balance the energy systems to maximize the energy output. Train aerobic capacity to a maximum and then adjust the anaerobic capacity to allow the utilization to as high a level as possible. This not possible if you assume everyone with the same threshold numbers are the same.

     

    The building blocks for an optimal performance are many and must be constructed in a proper sequence. They must recognize that each individual is different. Some of these building blocks are correct technique, positive mental attitude and a proper diet. However, the cornerstone for this building is precise physiological training. That is the main reason an athlete spends so much time in the water, on the bike, on the track or the road, in the weight room or wherever training is best conducted. How do you know if all those miles/hours of training are paying out?

     

    But what is appropriate physiological training? It is not volume alone, or those who put in the most hours/miles would always win. It is not intensity alone, or those who pushed themselves the hardest would always win. It is not this year’s fashionable workout, or everyone would use the magic workout, and no one would be better than any one else! It turns out that each individual has a distinct way of adapting, and any smart training plan must recognize individual differences. This is a fact of life. Each has to find his or her own best way to the proper balance of the energy systems and peak conditioning on the day that counts, race day.

     

     Further reading…

     

    Lactate metabolism: a new paradigm for the third millennium L. B. Gladden, July 1, 2004 The Journal of Physiology, 558, 5-30.

    Lactate and glucose interactions during rest and exercise in men: effect of exogenous lactate infusion. Miller BF1, Fattor JA, Jacobs KA, Horning MA, Navazio F, Lindinger MI, Brooks GA. J Physiol. 2002 Nov 1;544(Pt 3):963-75.

     

     

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