Slow-twitch vs. fast-twitch cells - discuss

More information on muscle fier recruitment and zone training is below. This is a very important aspect of efficient training. More is available in my book The Triathlete's Guide to Run Training, available at www.Fitness-Concepts.com Ken

Intensity & Muscle Fiber Recruitment
© 2004 by Ken Mierke

The single most critical factor in endurance training is intensity. In any structured training program, each workout should have a specific purpose. To achieve the ideal response from the body, the stimulation must be specific to the desired adaptation and must allow quick recovery for the next key workout. Intensity, more than any other variable, determines the body’s response to the training stimulus.

This absolutely does not mean that harder is better. The optimal training schedule for any athlete provides the lowest volume and intensity that will stimulate the desired adaptation, not the highest the athlete can sustain. This is a major paradigm shift for many endurance athletes who grew up hearing, “No pain, No gain.” If hill repeats at 450 watts stimulate increased aerobic capacity, then that is how fast those workouts should be performed even if he can perform the repeats at 470. Being a “tough guy” and always going harder and harder will not yield ideal results.

Tough guys never seem to get any faster, they just get tougher … and it seems like fast guys are always winning the races.

Training efficiently means balancing the cost and benefit of each workout. Every workout has a cost, in terms of recovery. Every workout also increases fitness. Efficient workouts provide training benefits that are worth the recovery cost. Every athlete at any point in time has certain recovery resources. While smart athletes develop habits to maximize these resources, they will always be finite, and need to be budgeted. Anything that is going to expend these resources needs to provide a proportionate benefit.

Recovery resources include, among other things:

• Glycogen Storage: Glycogen is the form of carbohydrate, stored in our muscles and in our liver that serves as the primary fuel for endurance exercise. Hard or long workouts expend tremendous amounts of glycogen and demand full fuel tanks at the beginning of the workout. Maintaining optimal intensity makes best use of this limited resource.

• Muscular Recovery: Muscles sustain damage during running workouts. Lactic acid accumulation damages the muscles chemically and impact stress damages the muscles mechanically, producing tiny tears called micro-trauma.

• Connective Tissue Damage: Every workout, but especially a run workout, stresses and damages connective tissues. These tissues need to heal and rebuild adequately between workouts.

• Injury Risk: Injuries are an ever-present risk in any workout, especially run workouts. During high-volume or high-intensity workouts, risk for injuries increases.

Maintaining optimal intensity during every workout is a key aspect of managing these risks. These are all limited resources, and running at the right pace during each workout makes the best use of them. This allows you to benefit maximally from each workout and gets you ready sooner for the next key workout.

Remember that it is the quality of the individual workout that makes an athlete stronger and faster, not just an accumulation of stresses. Many athletes train medium hard all the time. On their hard days, even if they put in 100% effort, they don’t get 100% speed because they are a little tired from yesterday’s workout or from an accumulation of weeks of training without quite enough recovery.

If an athlete should be producing 420 watts on hill repeats, but you keeps hitting 390 because he’s fatigued from yesterday, that is bad training. His legs don’t respond or improve from his 100% effort, they just respond to the 390. He is training himself to climb slowly even though he is working hard. That is bad training.

Muscle Fiber Recruitment

Each muscle in our bodies is composed of thousands of muscle fibers. These muscle fibers come in three basic types. Each of our muscles is composed of some combination of these three types, the percentage of each type depending on individual genetics.

Slow twitch muscle fibers are our endurance fibers. They can keep going all day long, but they are not big, fast, strong, or powerful. Slow twitch muscle fibers are able to burn either fat or carbohydrate for fuel, depending on the intensity.

Fast twitch muscle fibers are our sprint fibers. They are big, fast, strong, and powerful, but they fatigue very quickly. Fast twitch muscle fibers cannot burn fat for fuel.

Our muscles also have an intermediate fiber which produces more power than slow twitch fibers and has greater endurance than fast twitch fibers. These fibers are called F.O.G. fibers (fast oxidative glycolytic).

Every muscle in an athlete’s body is composed of many thousands of muscle fibers. When the muscle contracts, each fiber either contracts with its full force capability, or remains relaxed. When an athlete pedals at 50 watts, very few fibers are required to contract, but those that do contract just as powerfully as when he pedals at 700 watts.

After aerobic plateau, which requires several minutes at the beginning of each workout (and each shift in intensity during a workout), the athlete’s body will recruit muscle fibers according to the power or speed requirement of the activity. The endurance fibers will be recruited first. At low intensity only a few endurance fibers will be recruited. As intensity increases, the speed endurance fibers will be recruited next, and finally the sprint fibers. The more powerful fibers will be recruited in addition to, not instead of, the slow twitch fibers.

Training Intensity Zones

Seven zones for training intensity are described below. Each intensity zone stimulates a specific desired adaptation that will enable you to race more effectively. Make sure that every workout has a specific purpose and maintain the appropriate intensity to achieve that end.

The most efficient training intensities stimulate the muscle fibers in groups. Since each category of muscle fiber type is a relatively homogenous (though there is gradation even within the categories), they adapt to stimulation similarly. In addition, fibers within each category will have similar recovery qualities.

Zone 1: Active Recovery: Power / speed requirement demands recruitment of just a few slow twitch fibers. The goal is to maintain an intensity that is high enough to stimulate increased circulation to deliver nutrients to the muscles and to remove toxins, and hard enough to stimulate a growth hormone release (which speeds recovery), but not high enough to demand more recovery.

Zone 2: Basic Endurance Training: Aerobic threshold is the intensity at which almost all of the ST fibers are being used, but none of the F.O.G. (IIa) fibers or FT (IIb) fibers are required to be recruited to meet the power demand. Basic endurance training is best accomplished at or slightly below aerobic threshold intensity. Most athletes don’t do enough of this type of training and go too hard when they try to.

Zone 3: Tempo Training: In Zone 3, the body is recruiting all of the ST fibers and some if the F.O.G. fibers, but not nearly all. Most athletes spend too much time training at this medium-hard intensity and would do better to slow down for most of their training time. The ST fibers can withstand enormous volume; the F.O.G. fibers can withstand moderate volume. Doing basic endurance training too hard is the primary cause of overtraining. Training in zone 3 instead of zone 2 reduces the threshold for overtraining significantly.

If adequate oxygen is available in proportion to the workload, ST fibers use fat as a significant fuel source. Recruitment of the FOG fibers reduces the availability of oxygen to the ST fibers. Since it requires more oxygen to release one calorie of energy from fat than from carbohydrate, fuel use shifts dramatically from a relatively even blend of fat and glucose burning to burning mostly glucose.

At this intensity the athlete isn’t going hard enough to really make them faster, but they are going hard enough to deplete themselves for tomorrow’s workout which is designed to make them faster.

This intensity zone can be effective for maximizing glycogen storage in the muscles and for preparing the body for the demands of higher intensity training. Zone 3 training should only be used early in base training, when there are no high-intensity workouts to interfere with, or during the build and peak periods when training for races which will take place at this intensity (race pace training). Zone 3 training has its place, but most athletes spend too much time at this intensity.

Zone 4: Lactate Threshold Training

Whenever an athlete exercises at any intensity, even walking, lactic acid (lactate) is constantly being produced. Fortunately, our bodies also constantly recycle lactate, actually burning it up and using it for fuel. As intensity increases, lactate production also increases. Lactate threshold is the highest intensity at which an athlete recycles lactate as quickly as it is produced, so that lactate does not accumulate. Muscle and blood levels of lactate are moderately high at lactate threshold intensity, but do not increase over time. Increasing pace just slightly will cause lactate to accumulate, increasing discomfort, damaging the muscles, and delaying recovery for tomorrow’s workout.

At lactate threshold intensity, the body recruits all of the ST muscle fibers and all of the FOG fibers, but does not recruit the FT (IIb) fibers. Just as the ST fibers can sustain much higher training volumes than the FOG fibers, the FOG fibers can withstand much, much greater training volume than the FT (IIb) fibers.

Lactate threshold training, in the right doses at the right time of season, is important for almost every cyclist and triathlete. For most athletes lactate threshold training has the best cost to benefit ratio of any type of training. This intensity is high enough to stimulate adaptations which dramatically increase speed-endurance, but because lactate is not accumulating, damage to the muscles and blood vessels is minimal and the recovery cost of the workout, if conducted properly, is modest.

At LT intensity, the FOG fibers create a lot of lactic acid, but only at a rate at which the ST fibers can burn it up and use it for fuel. Sustaining this intensity trains the FOG fibers to work more aerobically so that they produce less acid and trains the ST fibers to burn more acid, both of which push the threshold to a higher speed.

LT training is the only effective endurance training for the FOG. At lower intensities they are not recruited. At higher intensities, FT (IIb) fibers are recruited causing lactate to accumulate. This reduces the duration that the athlete can sustain the intensity and dramatically delays recovery.

Most athletes and coaches overestimate LT intensity and, when sustaining the correct pace, feel like they are not going hard enough. This creates a major problem, either limiting potential training volume or inducing overtraining. Training one percent over lactate threshold, at an intensity at which lactate accumulates slowly, causes much greater damage and requires much greater recovery time than the same duration at lactate threshold. Reducing training volume or suffering overtraining are poor tradeoffs for the slight benefits from the 1% increase in intensity. For a twenty to thirty minute segment, it does not feel that much harder. Lactate accumulates slowly, but continually, and does damage in the muscles that the athlete cannot necessarily feel. Several minutes into a segment at 101% of lactate threshold, lactate levels in the muscles and in the blood will be only slightly higher, but later in a long set they may be dramatically higher. Muscle damage and recovery time may increase enormously. A well trained athlete can sustain lactate threshold intensity for seventy five minutes or more with 100% effort, such as in a race.

Every athlete likes to think that they are more motivated than the rest. They will train harder, be more consistent and more disciplined. Coaches like to think the same about their clients. Remember though, no matter how passionate and motivated the client is, this is a finite resource. Budget it wisely. Correct use of LT training, generally a little on the conservative side, plays a big role in sustaining motivation.

Zone 5a Super-Threshold Training

In zone 5, the body recruits all of the slow twitch muscle fibers, all of the F.O.G. fibers, and begins recruiting the fast twitch (IIb) fibers. Intensity is slightly above lactate threshold, so acid is accumulating in the muscles and in the blood. At this intensity, acid accumulates gradually so that this intensity can be sustained for a long period of time. Well conditioned athletes race in zone 5a for 40K time trials or 10K runs.

Many athletes mistakenly train in zone 5a when they intend to be in zone 4 doing lactate threshold training. This is a costly mistake because the recovery time from zone 5a training much greater than from zone 4 training. Since acid accumulates very slowly in zone 5a, the difference between 4 and 5a is negligible when sustained for short periods of time. However, when sustained for moderate to long durations, the acid accumulation does significant damage to the muscle cells and requires significantly more recovery time.

Zone 5a training is excellent for improving acid tolerance. The muscles are trained to continue to produce speed efficiently despite the buildup of acid. This is a benefit, but it comes at a great cost in terms of the volume and intensity of other workouts.

Zone 5b Aerobic Capacity Training: Maxing the VO2

Maximal aerobic capacity or VO2 Max, the amount of oxygen consumed in one minute of maximal aerobic exercise, is widely considered the standard test for aerobic conditioning. Improving VO2 Max is a crucial step in maximizing endurance performance in any event lasting four minutes or longer. The higher an athlete’s VO2 Max, the greater the contribution of the aerobic system to energy production. This translates into greater endurance at any intensity.

Each muscle fiber type has both aerobic and anaerobic capabilities. Endurance fibers are mostly aerobic but do have some anaerobic metabolism. Speed-endurance fibers are more balanced. Sprint fibers are mostly anaerobic, but their aerobic abilities can still be important in racing. Aerobic capacity workouts improve the aerobic capabilities of the sprint muscle fibers.

Stimulating these adaptations requires maintaining an intensity that is high enough to demand recruitment of the sprint fibers, but low enough to enable the athlete to sustain the intensity for a duration that will stimulate aerobic adaptations in those fibers, instead of only anaerobic adaptations.

Zone 5c Anaerobic Endurance Training

Anaerobic endurance training involves near-maximal exertion of all of the muscle fibers. This type of training increases fuel storage for the ATP-PC energy system. This helps improve a rider’s sprint endurance – the distance over which he can sustain full sprint wattage.

Training at this intensity also improves the synchronicity of muscle fiber contractions. Humans are imperfect machines. Even the most skilled athletes can get nowhere near 100% of their muscle fibers firing simultaneously at just the right moment. Improving synchronicity increases peak power.

Training at this intensity also improves economy at every intensity. An athlete who time trials at 390 watts will expend less energy to produce 390 watts in a race by including 20-second efforts at 550 watts in his training.

Summary

A primary objective of intensity zones is training each category of muscle fiber type as a group. Fibers within each category are relatively homogeneous for many qualities, including response to the training stimulus (improvement) and rate of recovery following a workout. Training them together optimizes both stimulation and recovery.

Interesting article, thanks.

And thats why I do smaller climbs at around 120 on race day

You can't change what you have, you can only train them to be better. You're born with a preset amount of fast and slow. Your Type 2 fibers will not become type 1. Just use what ya got, push hard and pick the type of racing better suited. In your case, sprints will be the best chance for you to place well.

Here's a quote from Performance Cycling, by David Morris:



Unfortunately it's been 2 years since I read this book through and I don't remember specific references as to how to train fast-twitch fibers to convert to slow-twitch fibers. I would highly recommend this book, however, and you may find the answers there.

bock

That was the conventional wisdom until recent research has shown otherwise (see my post above). Good news for those who previously thought they were just not built for endurance events!

bock

Any research on NO twitch fibers? "Cause I think i have a bunch of those.

Runnergirl, you can't change your genetics sand get more ST fibers, but you can train those to improve dramtically. I'm just the opposite. I started road racing before triathlon and my training partner told me that I was the only rider he knew who could time trial at 25 and spring to 25 1/2.

Fast-twitchers need to be very careful with intensity on long rides and runs. Almost every athlete goes too hard when trying to do basic endurance workouts and fast-twitchers pay a bigger price for this mistake. When you are going hard, go hard. WQhen you are going easy, go easy. Below is informationon how to train the endurance component of FT fibers. Ken

Aerobic Capacity Training: Maxing the VO2
© 2003 by Ken Mierke

Maximal aerobic capacity or VO2 Max, the amount of oxygen consumed in one minute of maximal aerobic exercise, is widely considered the standard test for aerobic conditioning. Improving VO2 Max is a crucial step in maximizing endurance performance in any event lasting four minutes or longer. The higher an athlete’s VO2 Max, the greater the contribution of the aerobic system to energy production. This translates into greater endurance at any intensity.

Each muscle fiber type has both aerobic and anaerobic capabilities. Endurance fibers are mostly aerobic but do have some anaerobic metabolism. Speed-endurance fibers are more balanced. Sprint fibers are mostly anaerobic, but their limited aerobic abilities can still be important in racing. Aerobic capacity workouts improve the aerobic capabilities of the sprint muscle fibers.

Stimulating these adaptations requires maintaining an intensity that is high enough to demand recruitment of the sprint fibers, but low enough to enable the athlete to sustain the intensity for a duration that will stimulate aerobic adaptations in those fibers, instead of only anaerobic adaptations.

Aerobic Capacity Intensity

To improve aerobic capacity in a well-trained athlete, training should take place at about 95% of VO2 Max. While the results of a VO2 Max test can be useful in pinpointing optimal training pace for aerobic capacity training, research shows that field testing determines optimal intensity very effectively.

Since field testing incorporates psychological as well as physiological variables, and since it is more practical, that method is used most frequently. Perform a time trial of six to eight minutes. Make sure the athlete is well rested before the time trial. Monitor speed or wattage and heart rate during the test. The highest intensity that can be sustained for six minutes produces optimal results for aerobic capacity workouts. We refer to this as six minute time trial pace (TT6) for running or critical power 6 (CP6) for cycling.

The intensity (heart-rate and/or speed) determined by the field test is how fast all aerobic capacity workouts should be conducted. It is not correct to go faster when performing shorter intervals or repetitions and it is not correct that intervals should be performed as fast as possible for this type of training. Training beyond the optimal intensity has no additional benefit to the aerobic system, yet comes at a great cost in terms of the body’s recovery resources. Energy to increase output above 6-minte race pace is derived almost 100% from anaerobic sources and therefore will not increase aerobic capacity. When in doubt, err on the conservative side with aerobic capacity training. It can be a powerful tool, but a little bit goes a long way.

The pace determined by your field test could feel too easy for several reasons. You could have improved conditioning or economy since your last test. You could have used less than full effort in the test. Or you could be accustomed to performing workouts too fast for an endurance athlete. Before you increase your interval pace, prove that you need it with a faster field test.
Duration and Work/Rest
To increase aerobic capacity, an athlete needs to spend considerable time performing near maximal oxygen consumption. Raising exercising VO2 involves both an intensity component and a duration component. Even when performing at a very high intensity, it takes one minute and forty seconds to two minutes to elevate oxygen consumption to the levels necessary to optimally increase aerobic capacity. So, performing six sets of two minutes at aerobic capacity pace and twelve minutes near max VO2 are quite different. There are two ways to maintain oxygen consumption near VO2 Max for extended durations in a workout: repeat training and interval training.

Repeat training involves relatively long repetitions with basically full recovery between sets. Since approximately two minutes are required to optimally elevate VO2, repeats need to be considerably longer than two minutes. In a sense, the benefits are only starting at the two minute point, when oxygen consumption has climbed to near maximal levels.

One workout using repetition training would be four repetitions of four minutes each at TT6 pace or CP6 wattage. Obviously this is an extremely taxing workout. Since each repetition yields about two minutes performing near maximal aerobic capacity, this workout will provide about eight minutes near max VO2. This type of workout should be used primarily during late Build and Peak periods. It is also effective in developing lactate tolerance and in preparing an athlete psychologically for the demands of racing. Be conservative with this training because it is extremely costly to the athlete both physically and psychologically.

A second way of maintaining elevated VO2 for extended periods is interval training. Performing shorter repetitions at the same intensity (TT6 or CP6), but minimizing recovery between repetitions leads to increasing VO2 throughout the set. Reducing the recovery causes the athlete to begin each repetition at a higher VO2 than the previous repetition, so that through most of the set the desired near-maximal oxygen consumption is attained much earlier in each repetition. In the example in the previous paragraph, the athlete performed at TT6 pace or CP6 wattage for twenty minutes but only about half of that time was spent near max VO2. An athlete performing a set of short-rest intervals may keep VO2 elevated for a much greater percentage of the set duration.

Be careful not to perform at a higher intensity during shorter intervals. Going above TT6 or CP6 will not increase aerobic gains, but will increase the recovery cost dramatically.

The classic aerobic capacity set is five sets of three minutes at TT6 pace or CP6 wattage with a three minute recovery. This is a hard workout that needs to be built up to.

Another very effective aerobic capacity workout is called 30/30s. This workout involves 30 second repetitions at TT6 pace or CP6 wattage with 30 second recoveries between each repetition. This is an extremely efficient workout. The benefits are extremely high and aerobic capacity and high-speed endurance may be increased dramatically, but the cost of the workout (recovery cost and psychological cost) is relatively low since acid doesn’t accumulate to a great degree because of the short repetition duration and the acid can be recycled during the recovery periods.

As repetitions get longer, work-to-rest ratio must increase. Even with a short work repetition, such as 30 seconds, 30 seconds of recovery is not enough time for a huge drop-off in VO2. With a longer, say two minute, repetition duration, a 1:1 work-to-rest is not great enough. I generally limit interval recovery to about a minute between repetitions and consider anything over a minute to be almost full recovery. Even after a hard repetition, oxygen consumption decreases dramatically with significantly more than a minute recovery and the next repetition will require the full two minutes to elevate to near max.

Another effective workout that combines lactate threshold training and aerobic capacity training involves running a segment at LT followed immediately by a segment at TT6 pace or CP6 wattage. This type of workout is effective because oxygen consumption is already considerably elevated at the beginning of the TT6 or CP6 repetition, so the athlete reaches the near-max oxygen consumption much more quickly than when starting from rest or from basic endurance pace.

Begin aerobic capacity training conservatively. It will probably be a significant increase in intensity for most athletes. I recommend starting with short-rest intervals, like 30/30s, for about 8-12 minutes of “on” time and building volume slowly, but consistently. Gradually shift to sets with longer repetitions. Monitor your recovery response carefully because it varies considerably between individuals. Many athletes, even those who tolerate high training volume very well, break down easily with aerobic capacity training.

Ken Mierke, head coach of Fitness Concepts (www.Fitness-Concepts.com) is Director of Training for Joe Friel’s Ultrafit and author of Training for Time Trials (due out 2006) and The Triathlete’s Guide to Run Training.. Ken can be contacted at [email protected].

Runnergirl

Fast twitch fibers can be converted to slow twitch fibers. This has been demonstrated in animal studies hundreds of times. Difficult to do human studies. Nobody wants to donate slices of muscle for analysis! Weight training is NOT a good way to convert muslce fibers. The answer is more endurance training, not weight lifting. It is more likely that you will increase the aerobic capacity of your fast twitch fibers before converting any slow twitch ones.

Mike

Crazyness...

My words were spoken from my olympic lifting/powerlifting background....

Ok- so when you say endurance training what exactly do you mean by that?  I've run 2 marathoons so it's not that I can't do the distance.  I can do the distance, it's just that I'm slow.  But seriously, I hate having fast twitch fibers because it really sucks for long distance races.  I blame in on my dad because he used to also be a sprinter in high school so I know I got these muscles from him.  People make comments like "I thought you'd be faster than that" and I honestly can't help it.  It's not that I don't push myself and try because I always do- within reason.  But I always tire before others who it's obvious they have more slow twitch.  Although, I know I can smoke them with sprints   One day I'd like to go out to the track and show them what I got!

Edited by runnergirl28 2005-08-22 9:09 PM

endurance training is base training. in other words training at a high cadence in a low heart rate zone (z1,z2)

Just a question, do you train with a heart rate monitor?

I have Old Twitch, and sometimes Intoxicated Twitch muscles, actually happy to have something twitch sometimes..

All my fast twitch (loved to sprint when I was young) have really faded....I'm amazed about Master Track and Field athletes that can still blaze a 100m.  I'd be crumpled on the track with Pulls.

Edited by BellinghamSpence 2005-08-22 11:36 PM

Nice morning laugh spence.....I am def. slow twitch. I have basically one speed, but could go for days.

Yup best hundred bux I've ever spent.

Ken, what's your response to the research that has shown (even in humans) that you can change fast-twitch fibers to slow-twitch, and vice versa?

Also, you mentioned three types of muscle fibers. I have read that within the scientific community that studies muscle fiber types, fibers are no longer divided into one of three groups but are thought to exist along a continuum ranging from the fastest, most fatigable to the slowest, most fatigue resistant. This doesn't seem to jive with your theory of working each type of muscle fiber independently.

I'm no physiologist, so maybe I'm missing something. But I'm curious to hear your explanation of the two points above.

bock

Good comments and questions. Fiber type has always been along a continuum. Even within each of the three fiber types, individual fibers will vary in their endurance/sprint characteristics.

Genetics plays a significant role in fiber type. If we take a slow twitch fiber and a fast twitch fiber in a rat and switch the nerves that innervate the fiers, the fiber type will switch.

Fiber types are generally established by staining muscle cells with a dye which darkens oxidative enzymes. Fibers with more slow twitch characteristics will appear darker. There is no perfectly discrete way of labeling fibers. We know this is a man and this is a woman - the difference is discrete. What is a tall man? 5'10, 6'2, 6'6???

We have 2 paradigms, neither of which is either right or wrong.

The nerve which inervates a particular muscle fiber will give that fiber tendencies toward endurance (slow twitch), speed-endurance (FOG), or sprinting (FT). That we cannot control and that has a profound impact on an athlete's potential. After dominating in the Olmpic games, Florence Griffith Joyner decided to train for the next Olympic marathon. I believe she averaged about 8 minute miles in a 5K a few months later and realized that her dream was futile.

Training increases specific characteristics and capabilities of the cells, specifically toward what is stimulated by the workouts. This will move the fiber along the endurance-power continuum in the direction of the training. Whether this is enough to move the fiber into another category or not has more to do with defining the categories than with the basic ideas of fiber type and genetics. I can train a sedentary person's ST fibers to be stronger than their FT fibers used to be and I can train their FT fibers to have more endurance than their ST fibers used to have. The genetically predetermined innervation of those fibers still plays a huge role in the maximal capacity for either endurance or power.

I see this in testing athletes I coach, some of whom will prioritize an ironman one year and an olympic distance race the next. Aerobic threshold and lactate threshold intensities will fall at very different percentages of max during these years. That said, every athlete I have ever had has had a predisposition to speed or endurance that I strongly believe is genetically influenced.

This is even more of an issue in road racing, where FT fibers and ST fibers have different, but equivalent benefits. Though anyone can improve their sprint, great sprinters are defintely born and not made. I ccoach a pro cycling team and we look indirectly at fier type when reviewing metabolic testing of the athletes. This helps determine optimal training for each rider, but also helps determine the rider's role on the team.

Ken

 Ok-  so basically I am pretty much screwed by haivng fast twitch muscles!  Ugh!  One more question- do fast twitch muscles build quick?  Reason I'm asking is because I gain muscle mass very easily- it sucks.  Check out my fast twitch cycling legs!





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Yes, FT fibers gain size more quickly than the other fiber types. Lots of people would LOVE to habe your problem. T keep from gaining muscle, avoid high torque activity - hand paddles swimming, low cadence riding, or long strides running. Use higher cadence and turnover cycling and running to gain speed and you won't over-work the FT fibers. As a gifted springter, you'll never win the Hawaii Ironman, but you may do very well even at longer distance races. Like 99.9% of triathletes, you''ll have to enjoy racing against yourself. Ken

Will, you're looking pretty hot in your avator..it's about time for a before & after photo, don't you think???

Thanks- I'll try to not use the big chain ring as much.  Today someone asked me how I bulk up?  I was like, uh, I can't really help it.  It's because of my muscle type.  Will weights (low weight, lots of reps) make me bulker, I'm assuming?  Maybe I need to do pilates and yoga more often??