Science Behind the Long Run - Activating Muscle Fibers

look up motor units and the size principal.

Airegin wrote:

Physiologically, I know I'm getting more capillary beds and increasing mitochondria size and number.

To make this sound simpler, let's say you use 5 different sets of slow twitch muscle fibers in an hour. Once you go beyond that, your body calls on set #6 and thus you won't get to use sets #9 or 10 unless you go longer.

Does this hold true regardless of pace? Can I activate set #9 in less time because I'm going faster? (does the pace fatigue earlier fibers more quickly?) Do I still activate set #6 in an hour if I'm jogging at 9-10 minute/miles or do they get activated in 30 minutes because I'm hammering.

Thank you. Please let me know if I need to re-word.

I would say yes, although it is a different stimulus running 16 miles @ 10 minute miles then say 14 @ 7 minute miles. Not better, just different.

I think you should be more confused so you can learn something. Read this thread.

http://www.letsrun.com/forum/flat_read.php?thread=2959804&page=0

Here's my understanding of the science related to long runs.How your body recruits muscle fibers is intricately and inseparably linked to the intensity of the exercise.If the pace is too slow, you are not providing enough stimulus, or it takes longer to achieve the same benefits.If the pace is too fast, your long run may be cut short, and worse, you may end up stimulating different systems or recruiting fast-twitch fibers.Besides muscles, capillaries, and mitochondria, their are other potential or real benefits of the long run:- mental/psychological endurance to make long runs seem shorter- physical endurance of joints, bones, tendons, and muscles adapt to absorb the long term pounding without long-term damage- glycogen depletion of the slow twitch muscle fibers to stimulate the release and use of glycogen stored in the unused (or underused) fast twitch fibers- using fat as an energy source- training/conditioning your brain to tolerate longer exercise as a normal activity

Airegin wrote:

Physiologically, I know I'm getting more capillary beds and increasing mitochondria size and number.

To make this sound simpler, let's say you use 5 different sets of slow twitch muscle fibers in an hour. Once you go beyond that, your body calls on set #6 and thus you won't get to use sets #9 or 10 unless you go longer.

Does this hold true regardless of pace? Can I activate set #9 in less time because I'm going faster? (does the pace fatigue earlier fibers more quickly?) Do I still activate set #6 in an hour if I'm jogging at 9-10 minute/miles or do they get activated in 30 minutes because I'm hammering.

Thank you. Please let me know if I need to re-word.

physiology wrote:

look up motor units and the size principal.

More and more were finding that the size principle is violated in numerous situations.

Is one of those situations the long run?

alummm wrote:

More and more were finding that the size principle is violated in numerous situations.

physiology wrote:

look up motor units and the size principal.

In short, we have no idea.

It's doubtful, but due to fatigue you will have more FT recruitment going on than would be predicted by Henneman's size principle at a moderate intensity.

We are talking about oxidative fast twitch fibers here, and they are very similar to slow twitch fibers, both types having a very high oxidative capacity. So it's inevitable that they are used at moderate paces.

Higher-intensity running is actually more conducive to mitochondrial proliferation than low-intensity running is. The main benefit to FT units arising from longer, slower runs is the fact that some glycogen depletion occurs in adjacent fibers whether they are actually recruited during the run or not, which stimulates enzyme production within all the fibers, ST and FT alike, and creates more efficient meshing of glycogen synthesis with other metabolic systems such as lipid breakdown.

For a better long run protocol, one which actually recruits more of the larger (but still oxidative) fibers along the spectrum, sometimes pick up the pace to around probable marathon pace for most of the last third to last half of the run, with a slightly faster last mile or two than that. This will count as a moderately hard effort day due to impact stress and possibly some fuel depletion, so adjust the remainder of the weekly schedule accordingly. Eventually, you'll need to do this (a faster pace for some of the long run) in any event due to glycogen sparing, which puts a damper on the stimulus for aerobic enzyme activity. Maybe alternate long run protocols, with one being a true long run at an easy pace throughout and the next one being 75% to 80% of that length (15 to 16 miles if your longest run is 20) but using the strongly-paced last half.

How about eight all-out-for-30-second efforts with a 2 minutes recovery intervals? This will be the next big thing...

Owen Anderson would rubber stamp the 8 x 30 seconds plan were it not for the fact that each rep would be farther than 20 meters.

Actually, doing 6 to 10 buildups of about 15 seconds each during the last couple of miles of a regular easy-paced long run is another good way to recruit additional motor units after the smaller, fine-control (ST) units have done enough work to start getting fatigued. Use a buildup format on these and not a sudden change in pace or range of motion which might precipitate an injury after 90 or more minutes of easy running. Start with a pretty slow rep and touch on a little faster speeds with each successive buildup until a speed around 1,500 race pace is reached for a few seconds during the last few reps. Concentrate on staying smooth, tall and relaxed and using a deliberately quicker stride frequency and shorter ground contact time than was used during the bulk of the long run itself.