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发帖数: 41236 | 1 【 以下文字转载自 Tri 讨论区 】
发信人: Rodimus (变叔- 踏雪无痕), 信区: Tri
标 题: Low Carbo Training (zz)
发信站: BBS 未名空间站 (Wed Jan 4 15:20:23 2012, 美东)
排版有点乱，最好点进link看:
http://team.firstendurance.com/page/low-carbo-training-1
For years, well intentioned coaches and exercise physiologists have given
endurance athletes very strong recommendations to ensure high carbohydrate
intake during training and racing to optimize performance. Some recent
experimental evidence and the actual practice of some very successful
athletes has many of us rethinking our previous advice especially in regard
to training. As a coach, I sometimes encourage my athletes to purposefully
deplete glycogen stores during training or to limit the intake of
carbohydrate during certain endurance training sessions. One of the
researchers who has studied this idea presented a keynote lecture at the
American College of Sports Medicine conference in Denver a couple of years
ago regarding this practice titled: “Train low, compete high”. At the
time I was a little resistant, but the idea intrigued me – especially based
on the scientific findings.
It’s long been understood that a limiting factor to endurance racing is the
sparing of stored glycogen. Athletes cannot consume carbohydrates at the
same rate they can burn carbohydrates. So when the exercise bout is long
enough glycogen stores are depleted and exercise performance suffers. The
theory is that depleting glycogen during specific exercise bouts allows the
body to become more efficient at utilizing fat. It can take many weeks for
the body to adapt to low glycogen levels. The downside is that with low
glycogen levels it is difficult to conduct high intensity training sessions
since these require glycogen (carbohydrates) almost exclusively. What the
researchers propose is varying the intensity and the diet so high intensity
exercise bouts are done with high glycogen content and long slow endurance
training sessions are done with low glycogen content. This will help the
body adapt to a more efficient substrate utilization that can correlate to a
sparing glycogen and enhanced endurance. This ability to sustain endurance
with a higher reliance on fat utilization through training adaptation can
play a key role in reducing gastric distress associated with the need to
consume high levels of carbohydrates for long endurance sessions like
Ironman, Ultra running or Century rides.
In one of the studies that supports this idea, Bente Pederson of the
University of Copenhagen in Denmark looked at the responses to endurance
training using an interesting model. The subjects served as their own
controls by having one leg train each day for 1 hour and while the other leg
trained twice a day for an hour at each session every other day. All
subjects ate a controlled diet with 70% carbohydrate, 15% fat, and 15%
protein content throughout the 10-week study. The total amount of training
undertaken was equal in both groups, and the increases in maximal workload
during a progressive exercise test was equal in both as well. The biggest
difference in performance was found in a time to exhaustion test while
exercising at 90% of maximum power, which was increased nearly twice (190%)
as long for the twice a day training group compared to the daily 1 hour
training group. It is interesting to note that the resting muscle glycogen
content in the leg when performing the 2nd training session in the two a day
group was significantly lower at the start of each session. There were
also significantly increased mitochondrial and other metabolic enzyme levels
in the twice a day group leading the authors to conclude that training with
low muscle glycogen content increased both the responses to endurance
training and performance in a sub-maximal endurance task. (Pederson et al,
2005)
This practice seems to be supported by the records and anecdotal practice of
many very successful endurance athletes including Miguel Indurain (five
time winner of the Tour de France), some Kenyan distance runners, and from
American professional cyclist Tom Danielson in a recent interview on
Cyclingnews.com. Often, the goal of these training practices is to improve
the ability to use fat as a fuel source and spare glycogen stores. There is
also support for this idea in the training practices of elite athletes by
looking at the distribution of their training intensity. Several studies
show extremely large portions of training occurring at fairly low intensity,
with just a small percentage of training actually occurring at a high
intensity. The studies which have shown these practices include elite
performers in cycling, running, and rowing. (Seiler and Kjerland, 2006;
Lucia et al, 2007; Schumacher and Mueller, 2002; and Doust et al, 2006)
Another even more recent study using running as a training model replicated
the findings of increase endurance enzyme activity after 6-weeks of training
but did not find an associated improvement in endurance performance. (
Drust et al, 2009) This study did not necessarily have their subjects train
with low glycogen content, though, they simply did not have one group take
in any carbohydrate beverage during training while the control group did.
From what I see in the research, it is the training that is performed with
low glycogen content in the muscles that is key to the positive signaling
and adaptive responses. It is well known that reducing carbohydrate intake
during training increases the body’s ability to oxidize fats. It is also
well known that very high intensity training which relies almost exclusively
on carbohydrate as fuel can only be performed with adequate glycogen stores
. In order to maximize both performance during high intensity interval
sessions and also maximize the body’s metabolic responses to endurance
exercise it might be helpful to vary your training sessions relative to
glycogen content.
My suggestion would be to undertake high intensity interval training with
relatively high glycogen content…and ideally, to perform these training
sessions in the morning. Meaning, you want to be well fueled (high glycogen
content) prior to the start of your high intensity training sessions. For
multisport athletes, you should vary which sports you do in these morning
sessions to ensure that each sport has appropriate high intensity sessions
in your workout plan. Some days the morning high intensity session is
focused on swimming, some days running and some days cycling. In order to
prepare for your lower glycogen content workout later in the day it is
important NOT to fully replenish lost glycogen. I would recommend eating a
diet containing a low to moderate carbohydrate content (around 40 to 50% of
total calories) after these sessions. Then, later in the day a longer but
significantly lower intensity session focused on building pure endurance
should be performed later in the day with little to no carbohydrate intake
during the session (0- 40 grams per hour.). After the longer session, a
high glycemic recovery drink or a more typical moderately high to high
carbohydrate meal should be eaten (60-70% carbohydrate content). Following
this session the goal is to fully replenish lost glycogen so you are fully
fueled and prepared for your high intensity training session. For athletes
who only train once per day, you could modify this strategy to include a
high intensity interval session on the first day and then eat the low to
moderate carbohydrate meals following this session. The next day, your
training session should be the low intensity longer duration workout with
limited carbohydrate intake. After this session is completed, then a
moderate high to high carbohydrate diet should be maintained.
*This change in training fueling strategy may take 6-8 weeks before a
significant adaptation can occur.
Recommendation:
High Intensity Training Session: Begin session well fueled with glycogen
stores topped off. Finish session and do not consume a recovery drink.
Instead consume a balanced meal with only 40%-50% of calories coming from
carbohydrates.
Low Intensity long training session: Begin session low to moderately fueled,
where glycogen stores do not need to be topped off. Consume about 20-40g
carbohydrates per hour (about one serving of EFS drink) which should be less
carbohydrates than you would normally consume. The goal is to exercise and
finish the session with relatively low glycogen stores. Following this
session immediately begin to replenish lost stores through the use of a well
formulated recovery drink and/or high glycemic foods.
Racing: During your racing you should consume 50g+ of carbohydrates per hour
. With proper substrate adaptation this should be sufficient to fuel you
for long endurance races. |
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