One of the most common things we talk about when programming training sessions here at Dark Horse is the ability to utilise frequent bursts of high-intensity movements interspersed with a brief recovery. Why you might ask? Well as many many hours of reading research and then many more hours trialling the sessions and theories has shown, it’s nice to row at a low rate for sustained periods of time and work on your “aerobic fitness”, but in order to be able to produce a high-intensity workout you have to train at high intensity!
So, this week and next we’re talking all about where that higher intensity work comes into play in your training, and we’re giving you all the info you would need to be able to 1. Understand the energy supply needed for repeat sprint intervals 2. Give you some guidance on various approaches to attempting interval sessions and 3. Explain how sprinting can then be your best judge of the efficiency of your training.
That’s a lot to get through so let’s kick this one off!!
The biochemistry of sprints
Repeated sprint ability requires both a high maximal sprint power and the ability to maintain high maximal power during each subsequent sprint. A high maximal sprint power comes from the bodies ability to deplete large amounts of high energy phosphates at a fast rate. The human body stores around 25mmol/kg in dry muscle of adenosine triphosphate (ATP) (that’s what your body uses for immediate maximal effort work). Roughly 15mmol/kg is enough to fuel 1-2 secs of maximal work, therefore from a metabolic perspective, power is dictated by the amount and rate in which ATP is synthesised and then hydrolysed. Key point: the body will never fully deplete its APT stores as its there for basic cellular functioning also. So in a 30 secs sprint, you’ll deplete around 45% of your stores and between 10% & 30% in a 10sec sprint. As ATP is broken down, various metabolic pathways (energy systems) collaborate to resynthesize ATP in an attempt to maintain the peak rate of ATP turnover. As the brief recovery times between related sprints will lead to partial restoration of the stores, the amount of ATP resynthesized is likely to be an important determinant of the ability to maintain high maximal power during each subsequent sprint. With respect to the energy systems used to re synthesise ATP, there is a trade-off between power and capacity. The contribution of each energy system is determined by the exercise intensity, bout frequency, capacity and rest periods. The systems used are the Phosphocreatine (PCr), anaerobic glycolysis, and the aerobic /oxidative systems.
There are 80mmol/kg of PCr stored in the muscle, that’s around 3 times the amount of ATP and with a turnover rate of 9mmol/kg/sec PCr stores are largely depleted within 10secs of sprinting. The PCr system has the fastest turnover rate of ATP of all the energy systems as there is only one enzymatic reaction. Approx 85% of PCr stores are recovered within 2mins of rest, 90% within 4mins and 100% within 8mins Harris et al. (1976), furthermore this only happens if blood supply to the muscle is not occluded, which means active recovery during these sessions is highly suggested Hultman, Bergström, & Anderson, (1967).
During maximal exertion sprints, the rapid drop in PCr stores is offset by increased activation of glycolysis and glycogenolysis, the former relating to the breakdown of glucose from the bloodstream and the latter the breakdown of glycogen in the cytoplasm (yes we’re going that deep on this!). With intramuscular stores around 400mmol/kg, glycogen availability is not likely to majorly compromise ATP provision during the repeated sprints. Instead, it may be the progressive changes in the bodies metabolic environment. Gaitanos et al. (1993) showed that using 10 x 6sec sprints with a 30sec rest, showed that the first sprint used 50% PCr whilst the 10th used 80% PCr but was accompanied by a 27% loss in power output. The shortfall in energy is thus provided by the increase in the amount of aerobic energy ( a much lower yield of PCr and energy output).
Okay, that’s something to wrap your heads around!! Makes sure you are subscribed to our newsletter for part 2 next week and if you want to know more about energy systems and the type of training sessions we utilise for them join us in the Crew by clicking the link here http://babblecafe.com/workout
Yours in fitness, education and getting out of your comfort zone.
Gaitanos, G. C., Williams, C., Boobis, L. H., & Brooks, S. (1993). Human muscle metabolism during intermittent maximal exercise. Journal of applied physiology, 75(2), 712-719.
Harris, R. C., Edwards, R. H. T., Hultman, E., Nordesjö, L. O., Nylind, B., & Sahlin, K. (1976). The time course of phosphorylcreatine resynthesis during recovery of the quadriceps muscle in man. Pflügers Archiv, 367(2), 137-142.
Hultman, E., Bergström, J., & Anderson, N. M. (1967). Breakdown and resynthesis of phosphorylcreatine and adenosine triphosphate in connection with muscular work in man. Scandinavian journal of clinical and laboratory investigation, 19(1), 56-66.
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