Bodybuilding.com - Adaptations To Short Interval Sprint Training: Part 2!

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Did you know?
Obliques is an abbreviation for external obliques, the muscles to either side of abdominals that rotate and flex the trunk.

In the first article we talked about interval training and the metabolic system. Here I am going to focus on morphological adaptations that muscles undergo in response to short term sprint training.

Adaptations To Short Interval Sprint Training: Part 2!

By: Shannon Clark

Part 1 | Part 2

In the first part of this article, we looked at how interval training in the 10 second or less phase can impact the metabolic system of the exerciser. This is a very intense type of training that many people would have trouble performing, however, if completed, the benefits are quite numerous. You will be able to see similar benefits with intervals at a slightly lower intensity performed within the 10-30 second range, however, the adaptations will be slightly different.

Morphological Adaptations

Muscle Fiber Types

This classification system is based on the pH sensitivities of the muscle tissues ATPase activity. This property helps to determine the expression of the myosin heavy chain isoforms of the muscle fibers, which is responsible for the contractile characteristics (speed and force output).

Type IIb has the highest power outputs, type IIa is intermediate, and type I shows the lowest contractile speed and force. It has been shown that type IIb has ten times the maximum unloading shortening velocity of type I (Leveritt & Ross, 2001). So naturally, the higher the percentage of type IIb muscle fibers an athlete has, the better sprinter they will be.

Muscle Fibers: How Do They Differ?
Our body is composed of many different groups of muscles and each person has a unique composition of muscle tissue in their body. Read here learn about the 3 different muscle fibers.
[ Click here to learn more. ]

Switching Muscle Fibers

Further, studies have demonstrated that type IIb muscle fibers are the default gene that the body goes to when there is a lack of stimulation (rest). Also important, are intensity of stimulation and recovery given to the muscles.

Animal Tissue Study

In the first scenario, the muscle tissue was stimulated at a low frequency every 15 seconds.
In the second, it was stimulated at a high frequency every 15 seconds.
Finally, in the third scenario, the tissue was stimulated with a high frequency every 15 minutes (Ausoni S., et al., 1990).

After two months of stimulation, the low frequency, 15 second group demonstrated 79% type I fibers, the high frequency, 15 second group demonstrated 90% type I, and the high frequency, 15 minute group demonstrated 52% type I fibers.

Interpreting The Study

A possible reason for this is because when sprints are done with shorter rest periods, the aerobic system is called into play more and this system is more often characterized by type I fibers.

So even though you are still sprinting, it is beneficial for the muscles to keep an oxidative capability to perform with short rest intervals.

Further, the frequency of sessions will also play a factor. Performing sprint training 3 times a week will produce a far greater shift to type IIa fibers than performing sprint training twice daily will (Leveritt & Ross, 2001). Finally, genetic predisposition to certain types of muscle tissue fiber types will also influence how an individual reacts to a particular training protocol.

Muscle Size

Type II / I Ratio

It should be noted however, that it is not so much the size of the muscle fibers that determine how successful a sprint athlete is but more the type II/type I ratio of the muscle fibers.

Therefore, the greater the percentage of type II muscle fibers the athlete has, the most likely greater performance level they will have.

Hypertrophy Not Desirable

In either case, due to the nature of the energy systems involved, you will usually see more muscle mass on sprint training athletes than you will on endurance trained athletes, the extent however might not be as great as if you had been comparing an endurance athlete to a bodybuilder though.

The Sarcoplasmic Reticulum

What Is Ca+?
Ca+ stands for a positively charged Calcium ion. An ion is an atom or a group of atoms that has acquired a net electric charge by gaining or losing one or more electrons.
The Sarcoplasmic Reticulum (shown to the right in light blue) is responsible for releasing Ca+ in muscles.

The more developed the SR is, the faster this process can take place, and therefore, the faster the muscular contraction and relaxation rate will be. Generally, the faster the fiber twitch, the greater the volume of the SR. Also, along with the greater volume, they will also have a greater density of Ca+-ATPase enzymes which allow the muscle fiber to vary the force level it produces (Leveritt & Ross, 2001).

Neuron To Fiber Action Potentials

It appears as though this conduction velocity is largely correlated with muscle fiber type and fiber cross-sectional area (Leveritt & Ross, 2001). This measurement can be used to distinguish between endurance trained and sprint trained athletes quite accurately, as the slowest sprint trained athletes usually have much faster conduction velocities than even the fastest trained endurance athletes.

As studies are limited in this area though, it is hard to determine how much sprint training will increase muscle conduction velocity. However, the studies done so far have shown a consistent trend towards higher conduction rates after undergoing sprint training, particularly among those who were slow to begin with (Bianchi, S., Rossi, B. et al, 1997).

Conclusion

While reading all of these adaptations, keep in mind that this happens in response to very intense training. Most people don't reach the intensity level discussed in many of these studies to elicit these exact effects. While you definitely will experience some similar results with less intense sprint sessions, ones that many people are capable of performing, they most likely would not be of the same magnitude of those here.

References:

Ausoni, S., Gorzna, L., Schiaffino, S., et al. Expression of myosin heavy chain isoforms in stimulated fast and slow rat muscles. J Neurosci 1990; 10(1):153-60.

Bianchi, S., Rossi, B., Siciliano, G. et al. Quantitative evaluations of systemic and neuromuscular modifications induced by specific training in sedentary subjects. Med Sport: 50 (1).