...

Weight Category Sports

by taratuta

on
Category: Documents
39

views

Report

Comments

Transcript

Weight Category Sports
Chapter 49
Weight Category Sports
JACK H. WILMORE
Introduction
Most athletes are concerned with either attaining
or maintaining an optimal body weight and composition for their sport, or event within their
sport. For some athletes, increased body size
can be an advantage (e.g. basketball, rugby and
American football), providing that the increase
in size is the result of an increase in the athlete’s
fat-free mass. For other athletes, body size is not
nearly as important, but it is critical to maintain a
low relative body fat (% fat mass) and a high relative fat-free mass (% fat-free mass) to optimize
performance (e.g. distance running, soccer and
swimming). For still other athletes, their body
weight is dictated by a specific weight category
(range of weights) within which the athlete must
fall in order to be eligible to compete (i.e. weight
category sports).
Weight category sports include all sports in
which the athlete must compete within a given
weight category. Examples of weight category
sports are provided in Table 49.1. There are
also sports, or events within a sport, which are
weight controlled. In these sports or events,
competition is not organized by weight categories, yet the tradition of the sport or event dictates a slim figure, and thus a low body weight.
For example, in diving and figure skating, athletes are rated by judges as to how well they
perform a certain dive or skating routine. While
the emphasis in judging is to be placed on the
athlete’s performance, appearance does play a
significant role, and a leaner body is associated
with success. Examples of weight-controlled
sports are provided in Table 49.1. Weightcontrolled sports are included with weight category sports in this chapter as they share a
number of common nutritional concerns.
Weight-controlled sports are also addressed in
Chapter 39.
Weight category and weight-controlled sports
and events present a unique challenge from the
nutritional perspective (Wilmore 1992). Many of
these athletes are consciously trying to either
reduce weight or maintain a weight well below
what would be considered normal or optimal
for them. This leads to a variety of unhealthy
nutritional practices, including skipping meals,
avoiding specific foods or food groups which
are necessary for meeting the minimum daily
requirement for certain vitamins, minerals or
macronutrients, and the binge–purge syndrome,
including the use of diuretics and laxatives,
among others. This chapter will focus on nutritional issues unique to weight category and
weight-controlled sports. It will address techniques used to achieve weight loss and weight
maintenance for these sports, the health, physiological and performance consequences of weight
loss and maintenance through these techniques,
and practical considerations as to how to best
achieve and maintain an optimal body weight
for these sports.
637
638
sport-specific nutrition
Weight loss and
weight maintenance techniques
For both weight category sports and weightcontrolled sports, the rate of weight loss can be
rapid (i.e. within 24–72 h), moderate (from 72 h to
several weeks), or gradual (from several weeks
to months). In some sports, moderate and rapid
weight loss will occur many times over a single
season. Tipton has stated that in wrestling, this
process can be repeated between five and 30
times per season (Tipton 1981). Thus, the consequences of not only an acute period of moderate
or rapid weight loss must be considered, but also
the cumulative effects over the course of a season
where there are multiple bouts of weight loss and
Table 49.1 Examples of weight category and weightcontrolled sports and events.
Weight category sports
Weight-controlled sports
Body building
Boxing
Horse racing (jockeys)
Martial arts (e.g. judo,
karate)
Rowing
Weight lifting
Wrestling
Dance (ballet)
Distance running
Diving
Figure skating
Gymnastics
Synchronized swimming
weight regain, or what has been termed weight
cycling. The magnitude of the weight loss per
cycle can also be substantial. Steen and Brownell
(1990), in their survey of 63 college wrestlers and
368 high school wrestlers, reported that 41%
of the college wrestlers reported weight losses of
5.0–9.1 kg each week of the season while 23% of
the high school wrestlers lost 2.7–4.5 kg weekly.
For sports like wrestling, where both rapid and
moderate rates of weight loss are used, the techniques for achieving a given weight loss are quite
varied. Horswill (1994) has listed a number
of common methods of weight loss used by
wrestlers which are presented in Table 49.2. The
technique of negative energy balance is common
across rapid, moderate and gradual rates of
weight loss. Dehydration, purging and the other
techniques listed in Table 49.2 are most common
for rapid weight loss, but can extend across the
moderate rate of weight loss category as well.
Establishing a negative energy balance is the
preferred technique for weight loss. However,
this technique has limited efficacy when the
athlete must lose weight in a short period of time.
Ideally, the athlete will establish a goal weight
well in advance of his or her need to achieve
that weight. A negative energy balance of
2100–4200 kJ (500–1000 kcal) daily is ideal, and
this should be achieved through a balance of
Table 49.2 Methods of weight loss used by wrestlers. Adapted from Horswill (1994).
Method
Negative energy balance
Increase energy output
Decrease energy intake
Intentional dehydration
Metabolic
Thermal
Diuresis
Bloodletting
Purging
Other
Example
Weight loss
compartment
Body cell mass
Aerobic training
Diet, fasting
Body water
Exercise
Sauna, sweat suit, rubber suit
Diuretics, high-protein diet
Laxatives, vomiting
Haircut
Inversion*
Gastrointestinal tract
Body cell mass
* Inversion involves the wrestler standing on his head to redistribute his blood and body fluids, which some
wrestlers believe affects the scale reading.
weight category sports
639
Fig. 49.1 Rapid weight loss to
make weight for competition can
pose health risks and can impair
performance. However, as long as
competitors perceive an
advantage, the practice will
persist. Photo © Allsport / D.
Leah.
increased energy expenditure and decreased
energy intake. The objective is to reach the
desired goal weight over a reasonable period of
time, minimizing the potential loss of fat-free
mass (Wilmore 1992).
It has been clearly established that for both
rapid and moderate rates of weight loss, a substantial percentage of the weight loss, i.e. 50% or
more of the weight, can be derived from the fatfree mass, predominantly from the total body
water and protein stores. In fact, with very low
energy diets (i.e. 1680–3360 kJ · day–1, 400–
800 kcal · day–1) or low energy diets extended
over longer periods of time, water and protein
can still constitute a substantial percentage of the
weight lost. Keys et al. (1950), in their classic
series of studies on human starvation, fed nonobese adult men a test diet of 6570 kJ · day–1 (1570
kcal · day–1) for 24 weeks. The subjects’ diet
which maintained stable weight prior to going
on the low energy diet was 14.5 MJ · day–1 (3468
kcal · day–1). Over the first 11 weeks, approximately 40% of the weight lost was from fat, 12%
from protein, and 48% from water, with an
average rate of weight loss of 0.15 kg per day. In a
study of obese subjects, Yang and Van Itallie
(1976) reported an average rate of weight loss of
0.45 kg per day in obese subjects on a 5020 kJ ·
day–1 (1200 kcal · day–1) mixed diet over the first
5 days on the diet. Water comprised 66% of the
total weight loss. The relatively high contribution of water to initial weight losses is at least
partially the result of obligatory water loss
accompanying the metabolism of glycogen and
protein. Both glycogen and protein have hydration ratios of approximately 3–4 g water · g–1 of
substrate, both for storage and degradation (Van
Itallie & Yang 1977). Thus, athletes must be very
careful when dieting to maximize weight loss
while minimizing loss of fat-free tissue. Again, it
is important to combine exercise with diet to
achieve a given energy deficit per day. Including
exercise as a component of the energy deficit
attenuates the loss of fat-free mass when compared to diet alone (Ballor & Poehlman 1994;
Saris 1995).
Dehydration is the most widely used technique for rapid weight loss. Intentional dehydration is probably a better phrase to use since the
intent of the technique is specific to producing
body water loss, where unintentional dehydration is an unexpected consequence of negative
energy balance resulting from the obligatory
water loss associated with glycogen and protein
degradation. With intentional dehydration, both
metabolic and thermal techniques are intended
to induce water loss through sweating, although
an added bonus from exercise is the obligatory
water loss from depletion of the body’s glycogen
stores as discussed previously. Sweat losses,
640
sport-specific nutrition
which are composed mostly of water, can be as
high as 2–3 l · h–1 in men acclimatized to heat over
the short term, and up to 10–15 l · day–1 (Wenger
1988). Sauna and sudation or water vapourbarrier garments have been widely used to
promote sweating, and the subsequent loss of
water can be considerable. These techniques are
not without risk or negative consequences (Vuori
& Wilmore 1994), but dehydration remains a
powerful tool for major losses of weight in short
periods of time.
Dehydration can potentially be induced by the
use of a high-protein diet, as water loss has been
associated with a high-protein diet. However, the
contribution of a high-protein diet to water loss is
most likely associated with the fact that carbohydrate intake is reduced. This forces the body to
rely more on fats, with the resulting production
of ketone bodies. It has been clearly established
that an excessive formation of ketone bodies, or
ketosis, leads to diuresis. Also, as the intake of
carbohydrate is limited, muscle and liver glycogen stores are gradually depleted, resulting in
further water loss, i.e. the obligatory water loss
associated with glycogen degradation. Prescription diuretics are also used to induce dehydration, although these are on the banned list of
substances for use by athletes (Wadler & Hainline 1989). Certain foods, particularly alcohol
and those foods containing caffeine, have substantial diuretic properties. However, caffeine is
a banned substance when ingested in excessive
quantities, e.g. 6–8 cups of coffee in one sitting
(Wadler & Hainline 1989). Refer to Chapter 28 for
further details.
Bloodletting has been stated as a method used
for weight loss by wrestlers (Horswill 1994);
however, it is unclear if this is widely practised.
This was not mentioned as a technique for
weight loss in the comprehensive review of
Fogelholm (1994), and was not included as a
technique for weight loss in a large survey of
high school wrestlers (Weissinger et al. 1991).
Most likely, bloodletting is not widely used for
weight loss in athletes, as most athletes do not
like invasive techniques and recognize the
obvious physiological and performance disadvantages of blood loss.
Purging behaviours are discussed in detail in
Chapter 39, and will not be addressed in detail in
this chapter. Self-induced vomiting and the use
of laxatives are the primary purging behaviours.
These behaviours can lead to transient weight
losses, but have substantial clinical risk, are
potentially addictive, and can negatively impact
athletic performance. While haircuts and inversion might be used in hopes of reducing the
athlete’s weight, there is no evidence to support
the efficacy of these techniques.
Health consequences of weight loss
Athletes generally lose weight for one of three
purposes: to qualify for a specific weight category, to achieve a more aesthetic appearance,
and to improve performance potential. There are
a number of questions raised concerning the
potential for detrimental health consequences of
weight loss. While most critical attention has
been focused on rapid and moderate rates of
weight loss, there is also concern over gradual,
long-term weight loss. Each of these will be
addressed.
The primary concern with rapid and moderate
rates of weight loss is the consequences of severe
dehydration. Wrestlers have reduced body
weight by 4–5% in 12–24 h, and losses of up to
12% of body weight have been reported
(Brownell et al. 1987; Fogelholm 1994). The greatest percentage of the weight lost is from the total
body water stores. Water accounts for approximately 60% of the total weight of an adult man.
Thus, for a 70-kg man, total body water would
represent about 42 kg, or 42 l, assuming a water
density of 1.000. The intracellular fluid accounts
for about 67% of the total body water, or 28 l, and
the extracellular fluid accounts for the remaining
14 l. Of the 14 l of extracellular fluid, plasma
volume would account for 3 l and the interstitial
fluid would account for the remaining 11 l
(Guyton & Hall 1996). With rapid weight loss,
water is lost from each of the fluid compart-
weight category sports
4.0
11%
3.5
3.0
10%
Total body water loss (l)
ments. It has been estimated that the intracellular
compartment can contribute 30–60% of the total;
the interstitial fluid, 30–60% of the total; and the
plasma volume, 8–12% of the total (Mack &
Nadel 1996).
In a study by Costill et al. (1976), eight healthy
.
men cycled at 70% of Vo2max. in an environmental
chamber (Tamb = 39°C) until they were progressively dehydrated by 2%, 4% and 6% of their
initial body weight during a single, prolonged
exercise bout. After achieving each level of dehydration, the subjects rested for 30 min in a supine
position while a blood sample and muscle biopsy
were obtained. Plasma and muscle water contents were reduced by 2.4% and 1.2%, respectively, for each percentage decrease in body
weight. Figure 49.2 illustrates the changes in the
plasma, interstitial and intracellular fluid compartments at each level of dehydration.
What are the health implications of such major
changes in total body water? Of obvious concern
is the potential for disturbances in thermoregulation. Sawka (1992) concludes from his review of
the literature that hypohydration, consequent
to dehydration, causes greater heat storage (i.e.
increased core temperature) and reduces tolerance to heat strain. This is the result of reductions
in the rate of sweating and skin blood flow. Even
with decreased skin blood flow, there is still considerable displacement of blood to the skin for
cooling, making it difficult to maintain central
venous pressure and an adequate cardiac output.
Excessive sweat or urine loss could also result
in large losses of electrolytes, which could possibly have serious health consequences, such as
cardiac dysrhythmias. However, Costill (1977)
has concluded that even those electrolyte losses
can be large, they are largely derived from the
extracellular compartment, and that losses of
ions in sweat and urine have little effect on the K+
content of plasma or muscle.
Further, concern has been expressed as to the
effects of chronic dehydration on renal function.
Zambraski (1990), in a review of renal function,
fluid homeostasis and exercise, concluded that
exercise, particularly in conjunction with hypo-
641
39%
2.5
2.0
38%
1.5
10%
1.0
50%
60%
52%
0.5
30%
0
–2.2
–4.1
–5.8
Levels of dehydration (%)
Fig. 49.2 Changes in the plasma (䊐), interstitial ( )
and intracellular water ( ) compartments with
exercise and thermal dehydration of 2%, 4% and 6% of
body weight. Adapted from Costill et al. (1976), with
permission.
hydration, sodium deprivation, and/or heat
stress, presents a major stress to the kidneys.
Renal vasoconstriction and antinatriuretic
responses are increased in magnitude when
dehydration and/or heat stress are combined
with exercise. Exercise proteinuria and haematuria have been reported, indicating dramatic
changes in renal function. However, the incidence of acute renal failure is relatively small.
The long-term consequences of repeated
episodes of acute renal stress are unknown.
Repeated bouts of weight cycling have also
642
sport-specific nutrition
been postulated to have negative health consequences (Brownell et al. 1987). These would
include an increased energy efficiency, thus an
increased risk of weight gain, increased deposition of fat in the upper body (i.e. visceral fat),
lipid and lipoprotein disorders, reproductive
disorders such as delayed menarche and secondary amenorrhoea, and bone mineral disturbances consequent to secondary amenorrhoea.
Fortunately, most of these concerns have now
been clearly established to be unrelated to weight
cycling (van der Kooy et al. 1993; Anonymous
1994; Jeffery 1996).
Athletes attempting to maintain a body weight
which is lower than that which is normal and
healthy for them is also a cause for concern.
These athletes are often in a state of chronic
energy deficit (i.e. energy expenditure > energy
intake for many days, weeks or months). In
female athletes, Loucks and Heath (1994a, 1994b)
have demonstrated that once the energy deficit
exceeds a certain critical level, reproductive and
thyroid function are suppressed, which might
serve as a trigger for athletic amenorrhoea (secondary amenorrhoea in the athletic population).
Amenorrhoea in athletes is associated with low
concentrations of 17b-oestradiol and progesterone, which are, in turn, associated with low
bone mineral density in the spine (Snead et al.
1992). The combination of disordered eating
(including energy deficit), amenorrhoea and
bone mineral disorders has been termed the
‘female athlete triad,’ with the assumption that
disordered eating can lead to menstrual dysfunction, which, in turn, can lead to bone mineral
disorders (Wilmore 1991). The female athlete
triad has become a topic of great concern and is
the focus of a recent position statement by the
American College of Sports Medicine (Otis et al.
1997).
Physiological and performance
consequences of weight loss
With rapid and moderate rates of weight loss,
there will be reductions in total body water,
muscle and liver glycogen stores, as well as in
other components of the fat-free mass (Oppliger
et al. 1996). For the most part, these athletes are
already very lean prior to weight loss, and so
very little of the weight lost will be derived from
the fat stores. In fact, Friedl et al. (1994) have
reported that there is likely a lower limit to the
loss of body fat with weight loss in lean individuals. In a group of 55 soldiers participating in an
8-week Ranger Training Course, those who
achieved a minimum relative body fat of 4–6% by
6 weeks demonstrated only small additional
total and subcutaneous fat losses in the final 2
weeks and lost increasingly larger proportions of
fat-free mass. Therefore, as the athlete reaches a
low total fat mass, there is a reduced likelihood of
further losses of body fat with weight loss. Consequently, the percentage of the actual weight
loss from the fat-free mass during rapid and
moderate rates of weight loss is likely to be high.
Generally, decrements in performance are associated with losses in the body’s fat-free mass
(Wilmore 1992).
Several recent papers have reviewed the
research literature on the effects of rapid and
moderate rates of weight loss on physiological
function and performance (Fogelholm 1994;
Horswill 1994; Oppliger et al. 1996). The results
of these reviews are summarized in Table 49.3.
Since there is typically an interval of time
between weigh-in and actual competition for
most sports, ranging from a few minutes up to
20 h or more, it is extremely important to understand how physiological function and performance respond following a variable period of
rehydration and replenishment of nutrients.
Unfortunately, while a great deal is known about
the effects of acute dehydration on physiological
function and performance, far less is known
about the regain in function and performance
with rehydration and intake of nutrients.
From this table, it is very clear that rapid or
moderate rates of weight loss can have major
effects on both physiological function and performance. What is less certain are the potential
changes that occur with rehydration and food
intake during the interval of time between
weigh-in and competition. It appears that some
weight category sports
643
Table 49.3 Alterations in physiological function and performance consequent to rapid and moderate rates of
dehydration. Data from reviews of Fogelholm (1994), Horswill (1994), Keller et al. (1994) and Oppliger et al. (1996).
Variables
Physiological function
Cardiovascular
Blood volume/plasma volume
Cardiac output
Stroke volume
Heart rate
Metabolic
.
Aerobic capacity (V o2max.)
Anaerobic power (Wingate test)
Anaerobic capacity (Wingate test)
Blood lactate (peak value)
Buffer capacity of the blood
Lactate threshold (velocity)
Muscle and liver glycogen
Blood glucose during exercise
Protein degradation with exercise
Thermoregulation and fluid balance
Electrolytes (muscle and blood)
Exercise core temperature
Sweat rate
Skin blood flow
Performance
Muscular strength
Muscular endurance
Muscular power
Speed of movement
Run time to exhaustion
Total work performed
Wrestling simulation tests†
Dehydration
Rehydration
Ø
Ø
Ø
≠
Ø*
?
?
?
´, Ø
´, Ø
´, Ø
Ø
Ø
Ø
Ø
Possible Ø
Possible ≠
´*
´, Ø
´, Ø
Ø*
?
?
Ø
?
?
Ø
≠
Ø, delayed onset
Ø
´
?
?
?
´, Ø
´, Ø
?
?
Ø
Ø
Ø
´, Ø
´, Ø
؆
?
?
Ø*
´ ؆
Ø, decrease; ≠, increase; ´, no known change, or return to normal values; ?, unknown.
* From Burge et al. (1993).
† From Oopik et al. (1996).
of the function and performance that was lost
during an acute episode of a rapid or a moderate
rate of weight loss can be regained within 5–20 h
providing ample food and beverage are available
and the athlete is willing to eat. There are still
many questions to be answered regarding the
total efficacy of eating and drinking during this
period between weigh-in and competition with
respect to regaining normal physiological function and performance. The issue of replacing carbohydrate postexercise is covered in Chapter 7,
and rehydration after exercise-induced sweat
loss is covered in Chapter 19.
Practical considerations for
weight loss
As stated in a previous section of this paper, the
ideal way to lose weight for competition is to
establish a goal weight several months in
advance of the start of the competitive season,
and achieve this goal weight by gradual reductions in body fat of not more than 0.45–0.9 kg ·
week–1 while maintaining or increasing the fatfree mass. Koutedakis et al. (1994) have shown
that weight reduction of the same magnitude
(6–7% of body weight) over 2 months vs. 4
644
sport-specific nutrition
months in the same athletes 1 year later
adversely altered fitness-related performance
parameters in international lightweight oarswomen. Unfortunately, for many athletes a prolonged weight loss protocol is not possible. Since
most of them are already very lean (low fat
mass), they are able to achieve their competitive
weight only by losing large amounts of fat-free
weight with minimal losses of fat mass. This is
accomplished primarily through decreases in the
total body water stores, and the muscle and liver
glycogen stores, both of which are critical to
successful performance. Therefore, the length of
time between the weigh-in and competition is
extremely important, as is the fluid and nutrient
replenishment protocol. While a solid data base
is not yet available, it would seem logical that the
longer the period of repletion of fluid and energy
stores, and the more fluid and energy the athlete
can ingest during this period, the better will be
the subsequent performance.
What might be an optimal rehydration/
refeeding protocol? Of primary concern would
be the need to replenish both fluid and glycogen
stores. Of secondary concern would be the
replacement of electrolytes lost during the
process of dehydration. However, electrolyte
replacement is essential for the restoration of
fluid balance (Maughan & Leiper 1995; Shirreffs
et al. 1996). Thus, it would seem logical to use
both a sports drink (5–10% carbohydrate and
electrolytes) plus a high-carbohydrate food
source such as sports bars (providing there is at
least 2–3 h before competition). The combination
of the sports drink and sports bar should provide
optimal replenishment for the time available.
Since there is not a good data base on this issue,
athletes should be encouraged to experiment
with different combinations to see what works
best for them, keeping in mind that they need to
replenish both fluids and glycogen.
Effective strategies to make weight would
include each of the following.
• Compete in an attainable weight category — do
not drop down to an unrealistic category.
• Lose most of the weight preseason, and lose it
gradually to maximize fat loss.
• Ideally, if you need to lose 10% of body weight,
lose the first 6% gradually during the preseason,
and the last 4% through dehydration 24–48 h
prior to competition.
• Eat a high-carbohydrate diet during training
and during periods of weight loss to maintain as
best as possible muscle and liver glycogen stores.
• Supplement vitamins and minerals if restricting food to lose weight.
• Maintain normal hydration during training,
except for the 24–48-h period before weigh-in if it
becomes necessary to dehydrate to make weight.
• Maximize the period of time between weigh-in
and competition to replenish both water and
energy stores.
References
Anonymous (1994) Weight cycling: National Task
Force on the Prevention and Treatment of Obesity.
Journal of the American Medical Association 272,
1196–1202.
Ballor, D.L. & Poehlman, E.T. (1994) Exercise-training
enhances fat-free mass preservation during dietinduced weight loss: a meta-analytical finding. International Journal of Obesity 18, 35–40.
Brownell, K.D., Steen, S.N. & Wilmore, J.H. (1987)
Weight regulation practices in athletes: analysis of
metabolic and health effects. Medicine and Science in
Sports and Exercise 19, 546–556.
Burge, C.M., Carey, M.F. & Payne, W.R. (1993) Rowing
performance, fluid balance, and metabolic function
following dehydration and rehydration. Medicine
and Science in Sports and Exercise 25, 1358–1364.
Costill, D.L. (1977) Sweating: its composition and
effects on body fluids. Annals of the New York Academy
of Sciences 301, 160–174.
Costill, D.L., Cote, R. & Fink, W. (1976) Muscle water
and electrolytes following varied levels of dehydration in man. Journal of Applied Physiology 40, 6–11.
Fogelholm, M. (1994) Effects of bodyweight reduction
on sports performance. Sports Medicine 18, 249–267.
Friedl, K.E., Moore, R.J., Martinez-Lopez, L.E. et al.
(1994) Lower limit of body fat in healthy active men.
Journal of Applied Physiology 77, 933–940.
Guyton, A.C. & Hall, J.E. (1996) Textbook of Medical
Physiology, 9th edn, pp. 298–299. Saunders,
Philadelphia, PA.
Horswill, C.A. (1994) Physiology and nutrition for
wrestling. In Physiology and Nutrition for Competitive
Sport (D.R. Lamb, H.G. Knuttgen & R. Murray), Vol.
7, pp. 131–174. Cooper, Carmel, IN.
weight category sports
Jeffery, R.W. (1996) Does weight cycling present a
health risk? American Journal of Clinical Nutrition 63
(Suppl.), 452S–455S.
Keller, H.L., Tolly, S.E. & Freedson, P.S. (1994) Weight
loss in adolescent wrestlers. Pediatric Exercise Science
6, 211–224.
Keys, A., Brozek, J., Henschel, A., Mickelsen, O. &
Taylor, H.L. (1950) The Biology of Human Starvation.
University of Minnesota Press, Minneapolis, MN.
Koutedakis, Y., Pacy, P.J., Quevedo, R.M. et al. (1994)
The effects of two different periods of weightreduction on selected performance parameters in
elite lightweight oarswomen. International Journal of
Sports Medicine 15, 472–477.
Loucks, A.B. & Heath, E.M. (1994a) Dietary restriction
reduces luteinizing hormone (LH) pulse frequency
during waking hours and increases LH pulse amplitude during sleep in young menstruating women.
Journal of Clinical Endocrinology and Metabolism 78,
910–915.
Loucks, A.B. & Heath, E.M. (1994b) Induction of low-T3
syndrome in exercising women occurs at a threshold
of energy availability. American Journal of Physiology
266, R817–R823.
Mack, G.W. & Nadel, E.R. (eds) (1996) Body
Fluid Balance during Heat Stress in Humans. Oxford
University Press, New York.
Maughan, R.J. & Leiper, J.B. (1995) Sodium intake and
post-exercise rehydration in man. European Journal of
Applied Physiology 71, 311–319.
Oopik, V., Paasuke, M., Sikku, T. et al. (1996) Effect of
rapid weight loss on metabolism and isokinetic performance capacity: a case study of two well trained
wrestlers. Journal of Sports Medicine and Physical
Fitness 36, 127–131.
Oppliger, R.A., Case, H.S., Horswill, C.A., Landry, G.L.
& Shelter, A.C. (1996) Weight loss in wrestlers: an
American College of Sports Medicine position stand.
Medicine and Science in Sports and Exercise 28, ix–xii.
Otis, C.L., Drinkwater, B., Johnson, M., Loucks, A. &
Wilmore, J. (1997) The Female Athlete Triad. Medicine
and Science in Sports and Exercise 29, i–ix.
Saris, W.H.M. (1995) Exercise with or without dietary
restriction and obesity treatment. International
Journal of Obesity 19 (Suppl. 4), S113–S118.
Sawka, M.N. (1992) Physiological consequences of
hypohydration: exercise performance and thermoregulation. Medicine and Science in Sports and Exercise 24, 657–670.
Shirreffs, S.M., Taylor, A.J., Leiper, J.B. & Maughan, R.J.
(1996) Post-exercise dehydration in man: effects of
volume consumed and drink sodium content. Medicine and Science in Sports and Exercise 28, 1260–1271.
645
Snead, D.B., Weltman, A., Weltman, J.Y. et al. (1992)
Reproductive hormones and bone mineral density in
women runners. Journal of Applied Physiology 72,
2149–2156.
Steen, S.N. & Brownell, K.D. (1990) Patterns of weight
loss and regain in wrestlers: has the tradition
changed? Medicine and Science in Sports and Exercise
22, 762–768.
Tipton, C.M. (1981) Consequences of rapid weight
loss. In Nutrition and Athletic Performance (ed. W.L.
Haskell, J. Scala & J.H. Whittam), pp. 176–197. Bull,
Palo Alto, CA.
van der Kooy, K., Leenen, R., Seidell, J.C., Deurenberg,
P. & Hautvast, J.G.A.J. (1993) Effect of a weight cycle
on visceral fat accumulation. American Journal of
Clinical Nutrition 58, 853–857.
Van Itallie, T.B. & Yang, M.-U. (1977) Current concepts
in nutrition: diet and weight loss. New England
Journal of Medicine 297, 1158–1161.
Vuori, I. & Wilmore, J.H. (1994) Adjuvants to physical
activity: do they help in any way? In Physical Activity,
Fitness, and Health (ed. C. Bouchard, R.J. Shephard
& T. Stephens), pp. 270–284. Human Kinetics,
Champaign, IL.
Wadler, G.I. & Hainline, B. (1989) Drugs and the Athlete.
F.A. Davis, Philadelphia, PA.
Weissinger, E., Housh, T.J., Johnson, G.O. & Evans, S.A.
(1991) Weight loss behavior in high school wrestling:
wrestler and parent perceptions. Pediatric Exercise
Science 3, 64–73.
Wenger, C.B. (1988) Human heat acclimatization. In
Human Performance Physiology and Environmental
Medicine at Terrestrial Extremes (ed. K.B. Pandolf,
M.N. Sawka & R.R. Gonzalez), pp. 153–197.
Benchmark Press, Indianapolis, IN.
Wilmore, J.H. (1991) Eating and weight disorders in the
female athlete. International Journal of Sports Nutrition
1, 104–117.
Wilmore, J.H. (1992) Body weight standards and athletic performance. In Eating, Body Weight and Performance in Athletes: Disorders of Modern Society (ed. K.D.
Brownell, J. Rodin & J.H. Wilmore), pp. 315–329. Lea
& Febiger, Philadelphia, PA.
Yang, M.-U. & Van Itallie, T.B. (1976) Composition of
weight lost during short-term weight reduction:
metabolic responses of obese subjects to starvation
and low-calorie ketogenic and nonketogenic diets.
Journal of Clinical Investigation 58, 722–730.
Zambraski, E.J. (1990) Renal regulation of fluid homeostasis during exercise. In Perspectives in Exercise
Science and Sports Medicine. Vol. 3. Fluid Homeostasis
during Exercise (ed. C.V. Gisolfi & D.R. Lamb), pp.
247–276. Benchmark Press, Carmel, IN.
Fly UP