Dietary carbohydrate, muscle glycogen, and power output during rowing training J. C. SIMONSEN, W. M. SHERMAN, D. R. LAMB, A. R. DERNBACH, J. A. DOYLE, AND R. STRAUSS Exercise Physiology Laboratory, School of Health, Physical Education, and Recreation, The Ohio State University, Columbus, Ohio 43210-1284 SIMONSEN, J.C.,W.M. SHERMAN, D.R. LAMB, A.R. DERNBACH, J. A. DOYLE, AND R. STRAUSS. Dietary carbohydrate, muscle glycogen, and power output during rowing training. J. Appl. Physiol. 70(4): 1500-1505, 1991.-The belief that highcarbohydrate diet*s enhance t,raining capacity (mean power output) has been extrapolated from studies that have varied dietary carbohydrate over a few days and measured muscle glycogen but did not assess power output during training. We hypothesized that a high-carbohydrate (HI) diet (10 g. kg body day-‘) would promote greater muscle glycogen content mass’ and greater mean power output during training than a moderate-carbohydrate (MOD) diet (5 g. kg body mass-’ . day-‘) over 4 wk of intense twice-daily rowing training. Dietary protein intake was 2 g. kg body mass-‘. day--‘, and fat intake was adjusted to maintain body mass. Twelve male and 10 female collegiate rowers were randomly assigned to the treatment groups. Training was 40 min at 70% peak 0, consumption (VO& (A.M.) and either three 2,500-m time trials to assess power output or interval training at 70-90% peak vo2 (P.M.). Mean daily training was 65 min at 70% peak Vo2 and 38 min at 290% peak Vo2. Mean muscle glycogen content increased 65% in the HI group (P < 0.05) but remained constant at 119 mmol/kg in the MOD group over the 4 wk. Mean power output in time trials increased 10.7 and 1.6% after 4 wk in the HI and MOD groups, respectively (P < 0.05). We conclude that a diet with 10 g carbohydrate kg body mass-l . day-’ promotes greater muscle glycogen content and greater power output during training than a diet containing 5 g carbohydrate kg body mass-’ . day-’ over 4 wk of intense twice-daily rowing training. However, a diet containing 5 g carbohydrate. kg body mass-‘. day-’ does not lead to glycogen depletion or impairment of power output during such training. l

l

l

physical

exertion;

fatigue

ATHLETES undertake daily high-intensity training to maximize their athletic performance. This high-intensity training requires muscle glycogen as a substrate, and muscle glycogen seemsto limit endurance capacity (1, 16, 27, 31). Therefore, athletes presumably must replenish muscle glycogen stores daily to train optimally. It has been recommended that athletes consume 70% of their energy in the form of carbohydrate (29), but analyses of athletes’ diets show that they typically consume a moderate-carbohydrate diet, deriving 4560% of their energy from carbohydrate (3,8,17,23,30). However, it is not known whether consuming a moderate-carbohydrate diet adversely affects the ability to train or perform on a

ENDURANCE

1500

long-term basis. It has been shown that preexercise muscle glycogen concentration can progressively decline (4, 19) and that perceived exertion is higher (4,19) and running economy (19) is lower when athletes consume moderate amounts of dietary carbohydrate, but few studies have examined the effects of chronic consumption of various amounts of dietary carbohydrate on performance. Phinney et al. (24) found that cycling endurance at 64% of maximal 0, consumption (Vozmax) was not adversely affected in subjects who consumed ~20 g of carbohydrate daily for 4 wk, despite reduced preexercise muscle glycogen levels. Phinney et al. (24) suggested that skeletal muscle can adapt to chronic reductions in glycogen stores. However, the exercise intensity used by Phinney et al. (24) was lower than that used by most serious athletes in training. We hypothesized that a high-carbohydrate diet (10 g kg body mass-’ day-‘) would increase muscle glycogen content and improve time trial power output compared with a moderate-carbohydrate diet (5 g kg body mass-l day-‘) in rowers undertaking 4 wk of intense twice-daily training. l

l

l

l

METHODS

Subjects. Twenty-two collegiate rowers (12 men, 10 women) volunteered to serve as subjects and provided informed consent according to institutional guidelines. Percent body fat, initial body mass, peak 0, consumption (VO,), and percent slow-twitch fibers are shown in Table 1. Hydrostatic weighing was used to determine the percent body fat. Lean body mass of the subjects was determined for the females and males in the 1st and 2nd wk of the study. Vital capacity was used to estimate residual volume. Repeated measurements of vital capacity and hydrostatic mass were determined until the variability of the readings was ~4%. The means for the three highest values were averaged. The Siri equation (31) was used to calculate percent body fat and lean body mass. Diet. The subjects were randomly assigned in a doubleblind design to either high- (HI) or moderate- (MOD) carbohydrate diets. The HI diet daily provided 10 g carbohydrate/kg body mass (70% of energy), 2 g protein/kg body mass (13% of energy), and 17% of energy from fat. The MOD diet daily provided 5 g carbohydrate/kg body mass (42% of energy), 2 g protein/kg body mass (15% of energy), and 43% of energy from fat. The diets contained common food items, but the HI diet included a liquid

0161-7567/91 $1.50 Copyright 0 1991 the American Physiological Society

Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (163.015.154.053) on July 27, 2018. Copyright © 1991 American Physiological Society. All rights reserved.

DIETARY

TABLE

1. Subject characteristics Body

Men Women

Mass,

Fat,

Body

n

k

%

12 10

78.3i13.0 6O.lH.3

9.2kl.O 20.2H.O

Values are means + SE. Muscle lateralis.

CARBOHYDRATE

VO,,

samples

Peak \jo2, l/min

4.3320.14 2.50+_0.08 were obtained

Slow Twitch, %

56.8k3.7 47.4k3.2 from

vastus

0, consumption.

glucose polymer supplement (Exceed Hi-Carb, Ross Laboratories, Columbus, OH) that supplied -29 and 41% of daily dietary energy and carbohydrate, respectively. The MOD diet included an artificially colored, flavored, and textured liquid placebo. The diets were analyzed using the Food Processor diet analysis program (ESHA Corporation, Salem, OR) to ensure that the diets met the recommended daily allowances for minerals, vitamins, and trace elements. Breakfast and dinner were consumed under supervision in the laboratory, and prepared lunches were provided daily for consumption at the subject’s convenience. Dietary fat was individually adjusted to maintain body weight and dietary carbohydrate and protein at the required levels. The subjects responded to a survey 2 days after the last day of training. The study instructions indicated that the subject’s responses would not detrimentally affect honorarium payments. Analysis of responses to the survey indicated that the subjects did not consume foods other than those provided in the prepared diet; however, two subjects indicated they did not consume lunch on one occasion. Training protocol. All subjects undertook 4wk of twicedaily training 6 days /wk. Training began - lmo after the end-of the competitive autumn season. The same weekly training protocol was repeated four times (Table 2) and was based on training recommendations for elite rowers (13). The morning workout was 40 min of cycling on a Monark cycle ergometer (weeks I and 2) or rowing on a Concept II rowing ergometer (weeks 3 and 4) at 70% peak VO,. The afternoon workouts on days 2, 4, and 6 each week began with 10 min of rowing ergometry at 70% peak 00, followed by a stan dard sequence of work-recovery intervals as follows: 2 X 10 min at 90% peak VO, with 3-min recovery intervals at a self-selected intensity, 5 min at a self-selected intensity, 3 X 5 min at 90% peak VO, with 2-min recovery intervals at a self-selected intensity, 5 min at a self-selected intensity, 4 X 3 min at 90% peak VO, with 1-min recovery intervals at a self-selected intensity, 10 min at 70% peNakVO,. In summary, for days 2, 4, and 6 each week, total daily exercise was 60 min at 70% peak VO, and 47 min at 290% peak VO, (107 min total exercise at 270% peak VO,). Maximal rowing performance was assessedon days I, 3, and 5 each week during the afternoon workouts and began with 15 min of rowing at 70% peak VO,. After l-3 min, three maximal 2,500-m time trials were performed during which verbal encouragement was given by the investigators, teammates, and coaches. Completion time to the nearest 0.1 s, mean power output to the nearest 0.1 W, and peak heart rate were recorded. A comparison of peak heart rates at the end of the time trials with heart rates at submaximal work loads during peak VO, tests

AND

ROWING

1501

TRAINING

indicates that the subjects attained 290% peak VO, during the time trials. Each 2,500-m time trial was separated by an 8-min recovery period at a self-selected intensity. After the third 2,500-m time trial, another 15 min of rowing at 70% peak 30, was completed. Accordingly, for days I, 3, and 5 each week, total daily exercise included 70 min at 70% peak VO, and -30 min at 290% peak Vo2 (100 min total exercise at 270% peak VO,). Pilot studies demonstrated that the 3 X 2,500-m time trials reduced muscle glycogen from 188 to 74 mmol/kg, indicating that these training sessionscaused substantial muscle glycogen degradation. N 0 workout was performed on day 7, but on days 14 and 2 1 rowing was performed for 10 min at 70% peak vo2, 15 min at 80% peak OO,, and 10 min at 70% peak To2 (35 min of total exercise). Water was provided ad libitum during all workouts. All subjects completed all training sessions. Peak VOW.Peak VO, was determined on the rowing ergometer before training and after the lst, 3rd, and 4th wk of training. Subjects rowed for 3 min at an individually adjusted load estimated to require roughly 50% peak VO,; the work load was then increased by 40 W for 2 min followed by 20-W increments for each of two subsequent 2-min intervals; finally, the subject rowed as hard as possible for another 2 min. VO, was determined with an automated open-circuit system that calculated VO, every 30 s. The highest value was considered the subject’s peak VO,. Inspiratory volumes were measured with a spirometer (RAM-9200, Rayfield Equipment, Chicago, IL) calibrated against a Tissot spirometer. The fraction of expired 0, was measured with an 0, analyzer (S-3A/l, Ametek, Pittsburgh, PA). The fraction of expired CO, was measured with a medical gas analyzer (LB-2, Beckman Instruments, Fullerton, CA). The analyzers were calibrated with a National Bureau of Standards calibration gas. The results of these tests were used to adjust training intensities for the subsequent week. Blood sampling and muscle biopsies. Blood samples were collected in the fasted state before the morning workout 3 days /wk during the study. Muscle samples from the vastus lateralis were obtained on days 1, 10, 19, and 26, immediately before the afternoon time trials, from alternate legs on altern ate weeks. The quadriceps muscle group has been identified as a major contributor to work produ .ction during rowing (9,12,14,20). Samples were quick-frozen in liquid N, and stored at -8OOC. Analysis of blood and muscle. For determination of muscle glycogen content, the frozen muscle samples were TABLE

2. Weekly training protocol Day 1

i-z. * *

2

3

4

40 min at 70% peak AT1

TT

t:t,

“TT:,

t:i

c5

6

7

Rest

\j,z

“;f;!

t;$

~~~~o~i: 0

ATl, aerobic training, 30 min at 70% peak vo2; AT2, aerobic training, 20 min at 70% peak Voz; LTT, lactate tolerance training, 47 min at 90% peak VO,; TT, time trials, three 2,500-m time trials. P.M. workouts included light recovery exercise. * Peak VO,. See text for complete training protocol.

Downloaded from www.physiology.org/journal/jappl by ${individualUser.givenNames} ${individualUser.surname} (163.015.154.053) on July 27, 2018. Copyright © 1991 American Physiological Society. All rights reserved.

1502 TABLE

DIETARY

CARBOHYDRATE

AND

ROWING

3. Muscle glycogen

1

94t7

HI MOD

115+10

Q&d o-o o-o

90

c

Dab Group

TRAINING

100

10

120+8 117t8

LO CHO HI CHO

80 370--

1.9

134+12 121-t9

26

155-t7 124&10*

Values are means f. SE in mmol/kg. HI, high-carbohydrate diet. (10 g. kg body mass-’ day-‘); MOD, moderate-carbohydrate diet (5 g. kg body mass-’ day-‘). * Significant difference between treatments. l

+I 60--

m g g

50--

y u 40--Jm c.3 k 30-1 o 20-%0--

O--

l

divided (5-10 mg) into three pieces and weighed (0.00 mg). Each sample was hydrolyzed in 2 N HCl (2 h at 100°C) and neutralized with NaOH. The glucose concentration of the hydrolysate was determined enzymatically (21). The intra-assay coefficient of variation was 2.2% for duplicates of the same muscle sample and 8.4% for triplicate samples of the same muscle. The interassay coefficient of variation was 3.1%. Muscle fiber types were determined by staining for myosin adenosinetriphosphatase by use of an alkaline (pH 10.4) preincubation as described by Padykula and Herman (22). Slow- and fast-twitch muscle fibers were counted (2200 fibers), and fiber-type percentages were calculated. Blood glucose was determined with the glucose oxidase method (model 2 Glucose Analyzer, Beckman Instruments). The mean coefficient of variation for duplicate samples was