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Le peptopro augmente l'endurance et réduit le catabolisme

Messagepar Nutrimuscle-Conseils » 19 Nov 2009 12:24

Carbohydrate and Protein Hydrolysate Coingestion’s Improvement of Late-Exercise Time-Trial Performance

International Journal of Sport Nutrition and Exercise Metabolism, 2009, 19, 136-149

Michael J. Saunders, Rebecca W. Moore, Arie K. Kies,
Nicholas D. Luden, and Casey A. Pratt

This study examined whether a carbohydrate + casein hydrolysate (CHO+ProH) beverage
improved time-trial performance vs. a CHO beverage delivering ~60 g CHO/hr.
Markers of muscle disruption and recovery were also assessed. Thirteen male cyclists
(VO2peak = 60.8 ± 1.6 ml · kg-1 · min-1) completed 2 computer-simulated 60-km time
trials consisting of 3 laps of a 20-km course concluding with a 5-km climb (~5%
grade). Participants consumed 200 ml of CHO (6%) or CHO+ProH beverage (6% +
1.8% protein hydrolysate) every 5 km and 500 ml of beverage immediately postexercise.
Beverage treatments were administered using a randomly counterbalanced,
double-blind design. Plasma creatine phosphokinase (CK) and muscle-soreness ratings
were assessed immediately before and 24 hr after cycling. Mean 60-km times
were 134.4 ± 4.6 and 135.0 ± 4.0 min for CHO+ProH and CHO beverages, respectively.
All time differences between treatments occurred during the final lap, with
protein hydrolysate ingestion explaining a significant (p < .05) proportion of between trials
differences over the final 20 km (44.3 ± 1.6, 45.0 ± 1.6 min) and final 5 km (16.5
± 0.6, 16.9 ± 0.6 min). Plasma CK levels and muscle-soreness ratings increased significantly
after the CHO trial (161 ± 53, 399 ± 175 U/L; 15.8 ± 5.1, 37.6 ± 5.7 mm)
but not the CHO+ProH trial (115 ± 21, 262 ± 88 U/L; 20.9 ± 5.3, 32.2 ± 7.1 mm).
Late-exercise time-trial performance was enhanced with CHO+ProH beverage ingestion
compared with a beverage containing CHO provided at maximal exogenous oxidation
rates during exercise. CHO+ProH ingestion also prevented increases in plasma
CK and muscle soreness after exercise.



At least three studies have reported that carbohydrate-protein (CHO+Pro)
ingestion during prolonged cycling might increase time to exhaustion more than
conventional carbohydrate (CHO) sport beverages (Ivy, Res, Sprague, & Widzer,
2003; Saunders, Kane, & Todd, 2004; Saunders, Luden, & Herrick, 2007). CHO
beverages in those studies were consumed at intake rates of 37-47 g/hr, with 9-12
g/hr of protein added to CHO+Pro beverages. Although these levels exceeded
Saunders, Moore, Luden, and Pratt are with the Dept. of Kinesiology, James Madison University,
Harrisonburg, VA 22807. Kies is with DSM Food Specialties, 2600 MA Delft, The Netherlands.
CHO/Protein Hydrolysate and Time-Trial Performance 137
typical ingestion rates of endurance athletes during exercise (Noakes, 1993), carbohydrate
levels in the beverages were below peak exogenous oxidation rates
(Jentjens, Achten, & Jeukendrup, 2004; Jentjens, Moseley, Waring, Harding, &
Jeukendrup, 2004; Jentjens, Venables, & Jeukendrup, 2004). It is thus unclear
whether endurance improvements in the CHO+Pro trials were the result of protein-
mediated
effects or additional caloric content. Romano-Ely, Todd, Saunders, and
St. Laurent (2006) reported no differences in time to exhaustion between isocaloric
CHO and CHO+Pro beverages. However, the CHO+Pro beverage in that
study contained subpeak carbohydrate levels (45 g/hr), so it is possible that protein
provided an independent metabolic benefit, because performance was equal
to CHO despite 20% less carbohydrate in the CHO+Pro beverage. Thus, further
study is necessary to determine whether performance benefits with CHO+Pro are
observed when carbohydrate ingestion occurs at maximal rates during exercise.
Van Essen and Gibala (2006) recently reported no difference in performance
between CHO (60 g/hr) and CHO+Pro (60 g CHO/hr + 20 g protein/hr) beverages
during a simulated 80-km cycling time trial. They concluded that CHO+Pro might
not improve endurance performance when beverages are ingested at high rates of
carbohydrate intake or when assessed during time-trial tasks. However, the exercise
protocol used in that study did not include an examination of performance
differences during the latest stages of exercise, when differences between treatments
could potentially be detected with greater sensitivity. As an example, any
treatment that promotes supplemental energy utilization late in exercise (i.e.,
when muscle glycogen is depleted) could theoretically improve performance
times without influencing early-exercise power output. For example, a 1-min
improvement in time-trial performance has great practical significance to competitive
cyclists. However, the sensitivity to detect this difference is quite small if
measured over a 2-hr trial (<1% difference) and could only be reliably detected in
studies with exceedingly large sample sizes. However, if this ergogenic effect
were the result of delayed fatigue in late exercise, the sensitivity to detect this
same effect over the final 15 min of the trial would be much greater, because it
could represent a difference of up to 6.7% between trials. Similarly, other investigators
have examined the efficacy of CHO beverages using time trials immediately
after prolonged exercise protocols at a fixed intensity (Mitchell et al., 1989;
Zachwieja et al., 1992). In addition, performance differences might not be
observed early in exercise because of lag time related to the timing of beverage
ingestion, substrate uptake and availability, and achieving threshold amino acid
concentrations that might be required to initiate ergogenic effects. Because of
these factors, the proportional benefits of CHO+Pro could potentially be much
greater in late exercise.
To date, no published studies have examined the effects of protein hydrolysates
on endurance performance. Hydrolysates containing small peptides (di- and
tripeptides) are absorbed faster than free amino acids or amino acids from intact
protein and hydrolysates containing larger peptides (Grimble, Keohane, Higgins,
Kaminsky, & Silk, 1986; Grimble et al., 1987). Although enhanced availability of
amino acids from small peptides has been known for over 20 years, testing of
hydrolysates containing such peptides was hampered by the bitter taste. Hydrolysis
production processes have recently been developed that include a proline-specific
protease, a unique enzyme that can cleave peptide bonds involving proline residues.
138 Saunders et al.
These processes effectively "debitter" the hydrophobic peptides known to be the
main source of bitterness (Edens et al., 2005), allowing the potential benefits of
carbohydrate-protein-hydrolysate beverages (CHO+ProH) to be examined during
exercise in beverages with an acceptable taste.
In addition to potential improvements in endurance performance, CHO+ProH
consumption might elicit metabolic alterations that influence recovery from exercise.
Koopman et al. (2004) reported that CHO+ProH ingestion during ultraendurance
exercise produced significant improvements in whole-body net protein
balance compared with CHO ingestion. In addition, a few recent studies have
reported attenuated markers of sarcolemmal disruption and muscle soreness when
CHO+Pro beverages are consumed during and after exhaustive cycling (Millard-
Stafford et al., 2005; Romano-Ely et al., 2006; Saunders et al., 2004). However,
none of these studies examined the effects of CHO+Pro ingestion on markers of
muscle disruption after time-trial protocols. Unlike time-to-exhaustion trials at a
fixed workload, the intensity of time trials varies considerably within the exercise
session, especially during hilly trials. Thus, although total work during prolonged
time trials might be very similar to that during time-to-exhaustion protocols,
varied-intensity
time trials might elicit altered rates of substrate utilization, and
the higher forces required to climb steep inclines might also affect muscle-damage
markers to a differing degree from time-to-exhaustion protocols.
The primary purpose of the current study was to determine whether a
CHO+ProH beverage improved performance during a prolonged cycle time trial,
compared with a CHO beverage. Beverages were matched at maximal rates for
exogenous carbohydrate oxidation (~60 g/hr), and the performance assessment
included an examination of late-exercise performance, when the putative effects
of CHO+ProH beverages were hypothesized to be greatest. A secondary purpose
of this study was to determine whether CHO+ProH ingestion reduced markers of
muscle disruption after simulated cycling competition versus a CHO beverage.
Methods
Participants
Thirteen recreationally competitive male cyclists participated in the study. Inclusion
criteria for the study included a self-reported weekly cycling frequency of >3
days/week over the preceding 2 months and a laboratory-tested VO2peak of >45 ml
· kg-1 · min-1. Before testing, participants completed informed consent and a comprehensive
medical questionnaire to determine the presence of any risk factors
associated with coronary artery disease. All participants were asymptomatic and
possessed fewer than two risk factors using ACSM guidelines (American College
of Sports Medicine, 2006). All procedures and protocols were approved by the
James Madison University Institutional Review board. Participant demographics
are provided in Table 1.
Procedures
VO2peak. Before the study intervention, participants completed a graded cycling
test on a Velotron Dynafit Pro cycle ergometer (RacerMate, Inc., Seattle, WA).
CHO/Protein Hydrolysate and Time-Trial Performance 139
During a 5-min warm-up at 100 W, they were instructed to adjust the fit of the
cycle to their desired specifications, using horizontal and vertical adjustments of
the seat and handlebars. These setting were recorded and replicated in subsequent
trials. Using previously described procedures (Saunders et al., 2004), the VO2peak
protocol was initiated at a workload below lactate threshold and increased 25 W
every minute until volitional exhaustion. Oxygen uptake was assessed continuously
throughout the test using a SensorMedics Vmax Spectra metabolic cart
(Yorba Linda, CA). The metabolic cart was calibrated before each test using
medical-grade
gasses of known concentrations and a 3.0-L calibration syringe.
VO2peak was recorded as the highest 30-s mean oxygen-uptake value obtained
during the test. Participant height and weight were measured using a stadiometer
and digital physician’s scale, respectively. Participants were measured in their
cycling clothing without shoes and socks.
Endurance Time Trials. All participants completed two computer-simulated
60-km time trials on the Velotron cycle ergometer, separated by 7-10 days. Each
trial consisted of three simulated laps of a 20-km course (see Figure 1), with over
407 vertical meters of climbing in each lap (1,222 m total). Each lap concluded
with a 5-km climb of ~5% average grade (8% maximum grade). The course was
designed as such to allow an assessment of performance during the overall trial
(60 km), final 20 km, and final 5-km climb. Performance times were recorded for
each of these trial segments. We hypothesized that performance differences
between treatments would be most noticeable during the late stages of exercise, as
described in the introduction of the article.
Participants arrived at the laboratory 2-3 hr after a light meal and were
instructed to eat the same pretrial meal before the next trial. They were asked to
refrain from consuming caffeine or any pain medications during all trial dates.
Participants were also instructed to consume a consistent diet for 48 hr before
each trial and to refrain from consuming unfamiliar foods or alcohol during this
period. The time of day of the trials varied between participants but remained
consistent for each participant, to limit the potential impact of circadian rhythms
between treatments. Participants were instructed to treat the trials as a competitive
event and refrain from heavy exercise (including resistance training) for 48 hr
before each exercise session.
Participants were familiarized with bicycle-ergometer operation during the
VO2peak testing but did not perform a formal practice trial of the course before their
first time trial. They could freely alter the workload of the ergometer at any time
Table 1 Participant Demographics
Variable M ± SEM
Age (years) 25.3 ± 2.4
Height (cm) 177.9 ± 1.8
Weight (kg) 73.0 ± 2.6
VO2peak (L/min) 4.4 ± 0.2
VO2peak (ml · kg-1 · min-1) 60.8 ± 1.6
140 Saunders et al.
throughout the trials by using a simulated gear shifter. The ergometer was electronically
braked, such that any change in "gearing" was offset by a proportional
change in flywheel resistance. Changes in cycling cadence or course topography
were similarly offset by changes in flywheel resistance. Ergometer workloads
were reported by the manufacturer to have <0.2% variation between repeated
trials. As a motivational strategy, participants were permitted to view their elapsed
performance times on the computer screen during the trials, as well as simulated
gearing and distance traveled.
Physiological Measurements. During each of the time trials, VO2, respiratoryexchange
rate (RER), heart rate, ratings of perceived exertion (RPEs), blood glucose,
and lactate were obtained at 10, 30, and 50 km. In addition, plasma creatine
phosphokinase (CK) and muscle-soreness ratings were assessed immediately
before and 24 hr after cycling.
VO2 and RER measurements were obtained using a SensorMedics Vmax
Spectra metabolic cart. Participants breathed through a mass-flow sensor connected
to the metabolic cart for 5 min at each of the time points. After 2 min of
equilibration, mean values for VO2 and RER were calculated as the 3-min average
from 2 to 5 min of data collection at each time point.
Heart rate was obtained using a Polar heart-rate monitor (Brooklyn, NY). It
was recorded as the 1-min average for each time point. Subjective RPEs were
obtained using Borg’s 6-20 point scale, after participants were instructed regarding
its use (American College of Sports Medicine, 2006).
Blood samples were obtained using finger sticks to acquire ~0.2 ml of blood
at each sampling. Glucose and lactate concentrations were determined in duplicate
Figure 1 - Course and measurement profile for the 60-km time trial consisting of three
consecutive laps of a 20-km course. Physiological measures included VO2, respiratoryexchange
rate, heart rate, rating of perceived exertion, glucose, and lactate.
CHO/Protein Hydrolysate and Time-Trial Performance 141
from whole blood using a YSI 2300 STAT automated glucose/lactate analyzer
(Yellow Springs, OH) after pretrial calibration.
Plasma CK was obtained before and 24 hr after the time trials as an indicator
of sarcolemmal disruption. Venous blood draws from the antecubital vein were
used to obtain approximately 4 ml of blood. Whole blood was spun in a centrifuge
at 7,000 rpm to separate plasma, which was frozen at -80 °C. Before analysis,
samples were thawed to room temperature (22 °C) and mixed through gentle
inversion. Plasma CK was analyzed using a Johnson & Johnson Vitro DT 6011 as
described previously (Luden, Saunders, & Todd, 2007; Saunders et al., 2004). In
addition, the 24-hr postexercise timing was used to allow an appropriate comparison
with previous studies, which have used time points ranging from 12-15 hr
(Saunders et al., 2004, 2007) to 24 hr postexercise (Luden et al.; Romano-Ely et
al., 2006).
Subjective ratings of muscle soreness were obtained before and 24 hr after
the time trials, using a 100-mm visual analog scale.
Beverage Treatments
Participants consumed 200 ml of treatment beverage every 5 km during the time
trials. The CHO beverage consisted of a 6% carbohydrate solution containing
equal amounts of glucose and maltodextrin. The CHO+ProH beverage contained
identical carbohydrate ingredients but also included 14.4 g of protein from a specific
casein protein hydrolysate (PeptoPro, DSM Food Specialties, Delft, The
Netherlands). During each 60-km trial, 132 g of carbohydrate was ingested, with
an additional 32 g of protein consumed in the CHO+ProH trial. Thus, carbohydrate
levels were matched between treatments at a level that provided approximately
60 g CHO/hr, which approximates the upper limits of exogenous carbohydrate
oxidation during exercise (Jentjens, Achten, & Jeukendrup, 2004; Jentjens,
Moseley, et al., 2004; Jentjens, Venables, & Jeukendrup, 2004). Therefore, potential
performance differences between treatments could be directly attributed to
protein, because additional carbohydrate would not be likely to provide additional
benefits in performance (Jeukendrup & Jentjens, 2000). Cyclists consumed an
additional 500 ml of beverage within 30 min of trial completion. Beverages were
treated with 0.5 g/L of vanillin to provide an identical vanilla flavor to both treatments.
Beverages were administered in a randomly counterbalanced, double-blind
design.
Statistical Analyses
Treatment differences in time were compared between treatments for each trial
segment (60 km, final 20 km, and final 5 km). As previously described, participants
were permitted to view their elapsed performance times during the trials to
provide motivation for peak performance. However, because they were competing
against their prior trial, this characteristic of the protocol contributed to a significant
order effect, whereby participants performed significantly faster (p < .05) in
their second trial, independent of the treatment used. Therefore, the following
statistical model was used to correct for this order effect:
Trial difference = ð¢i + ð£ + error
142 Saunders et al.
where ð¢i is the effect of treatment order and ð£ is the difference resulting from
treatment beverages. This is a simple regression model, with order of treatments
as the dependent variable. To facilitate comparisons with mean values in other
published studies, mean values for time are provided in Table 2 with and without
correction for the order effect. All other measured variables showed no trial-order
effect, so they did not require such a correction.
Physiological measurements obtained during exercise (VO2, RER, heart rate,
RPE, and blood glucose and lactate), plasma CK, and muscle-soreness ratings
were examined using two-way (Treatment ðs Time) repeated-measures ANOVAs
for each variable. Because CK results were not normally distributed, the results
were analyzed after log transformation of the post- and preexercise CK-level
ratios. To preserve comparability with other work, results are presented in their
original or back-transformed units.
All values are presented as M ± SEM, and all hypothesis testing was conducted
using an alpha level of p < .05. In the case of directional hypotheses
between treatments (i.e., improvements in performance and muscle disruption or
soreness with CHO+ProH ingestion), a one-tailed alpha was used. Two-tailed
alpha tests were used for all other statistical tests.
Results
Time-Trial Performance
Treatment differences in performance times for each trial segment are displayed
in Table 2, with and without correction for the order effect. The presence of protein
hydrolysate in the beverage explained a significant (p < .05) amount of variance
in performance times between trials during the final 20 and 5 km of the time
trial.
Physiological Data
Physiological responses to the exercise trials are included in Table 3. No significant
treatment differences were observed between CHO and CHO+ProH trials for
VO2, RER, heart rate, RPE, or blood glucose and lactate. In addition, there were
Table 2 Performance Differences Between Treatments
Time (min)
Measurement period CHO CHO+ProH
60 km 135.0 ± 4.0 (135.1 ± 4.1) 134.4 ± 4.6 (134.3 ± 4.5)
Final 20 km* 45.0 ± 1.6 (45.1 ± 1.6) 44.3 ± 1.6 (44.2 ± 1.6)
Final 5 km* 16.9 ± 0.6 (17.0 ± 0.7) 16.5 ± 0.6 (16.5 ± 0.6)
Note. CHO = carbohydrate; CHO+ProH = CHO plus casein hydrolysate. Reported M ± SEM are
corrected for a significant order effect, with raw scores in parentheses.
*Significant difference between treatments, p < .05.
CHO/Protein Hydrolysate and Time-Trial Performance 143
no significant Treatment ðs Time interactions in any of those measures. Main
effects from the ANOVA model were examined to determine whether physiological
measures changed over the course of the trial, independent of treatment effects.
No significant changes were observed in VO2 between 10 and 50 km. However,
heart rate, RPE, RER, and blood lactate and glucose all changed significantly over
time (Table 3).
Plasma CK and Muscle Soreness
No significant Treatment ðs Time interactions were observed for plasma CK and
muscle-soreness levels. Postexercise CK levels were not significantly different
between CHO (399 ± 175) and CHO+ProH (262 ± 88) treatments (Figure 2).
However, CK levels increased significantly from pre- to postexercise in the CHO
trial (from 161 to 399, p < .05) but not in the CHO+ProH trial (from 115 to 262
U/L, p = .08). Similarly, postexercise muscle soreness was not significantly different
between treatments (Figure 2) but increased significantly (p < .05) in the CHO
trial (from 15.8 ± 5.1 to 37.6 ± 5.7 mm) and not in the CHO+ProH trial (from 20.9
± 5.3 to 32.2 ± 7.1 mm; p = .19).
Discussion
The primary purpose of the current study was to determine whether a CHO+ProH
beverage elicited improvements in cycling time-trial performance versus a CHO
beverage matched at optimal levels of carbohydrate intake (~60 g/hr). The small
difference in overall 60-km performance was not statistically different between
treatments. However, as hypothesized in the introduction of this article, all the
performance improvement with CHO+ProH was observed in the final 20 km of
the trial, and most of it occurred during the final 5-km climb to the finish. As a
result, the presence of protein in the beverage explained a significant portion of
the variance in performance time for the final 20- and 5-km segments, and
CHO+ProH ingestion resulted in a 3% improvement in time for the final 5 km of
the trial. These findings have substantial relevance for competitive athletes,
because most cycling races are determined by time differences of considerably
less than 30 s. Although the total times were not significantly different between
treatments, this is probably related to the statistical sensitivity with which differences
between treatments can be detected. For example, the 30-s treatment difference
in final 5-km times represented a 3% improvement with CHO+Pro, whereas
the 42-s treatment difference in 60-km times was a 0.5% difference. As described
earlier in the article, a very large sample size would be required to detect this difference
with adequate statistical power, even though it represents a difference of
considerable practical importance to competitive athletes.
These findings corroborate previous studies reporting significant improvements
in time to exhaustion with CHO+Pro ingestion (Ivy et al., 2003; Saunders
et al., 2004, 2007). Similar to the current study, each of those studies compared
CHO+Pro beverages with CHO beverages matched for carbohydrate content.
However, because carbohydrate intake rates in the studies (37-47 g/hr) were
below peak exogenous oxidation rates, the ergogenic effects of CHO+Pro could
have been related to the additional calories delivered by protein, as opposed to
144
Table 3 Physiological Reponses During Exercise, M ± SEM
10 km 30 km 50 km
Variable CHO CHO+ProH CHO CHO+ProH CHO CHO+ProH
VO2 (mL · kg-1 · min-1) 43.7 ± 2.1 44.7 ± 2.2 42.5 ± 2.5 44.3 ± 2.7 44.9 ± 2.3 45.1 ± 2.2
Respiratory-exchange rate* 0.99 ± 0.01 0.99 ± 0.01 0.96 ± 0.01 0.97 ± 0.01 0.94 ± 0.01 0.94 ± 0.01
Heart rate (beats/min)* 159.8 ± 4.7 157.4 ± 5.1 161.5 ± 4.7 161.1 ± 3.8 165.2 ± 4.5 166.5 ± 4.5
Rating of perceived exertion* 12.2 ± 0.3 12.3 ± 0.6 13.5 ± 0.5 13.8 ± 0.4 14.5 ± 0.7 14.9 ± 0.5
Glucose (mg/dl)* 82.2 ± 3.1 81.8 ± 3.3 87.1 ± 3.4 87.5 ± 2.0 85.7 ± 2.5 87.3 ± 2.0
Lactate (mmol/L)* 3.1 ± 0.4 3.0 ± 0.4 2.5 ± 0.4 2.4 ± 0.3 2.3 ± 0.3 2.4 ± 0.3
CHO = carbohydrate; CHO+ProH = CHO plus casein hydrolysate.
*Significant main effect for time, p < .05.
CHO/Protein Hydrolysate and Time-Trial Performance 145
protein-specific mechanisms. However, as discussed previously (Saunders et al.,
2004), it seems unlikely that the relatively large improvements in time to exhaustion
reported in the studies (13-36%) could be explained by the relatively small
differences in calories between treatments. The current study did not compare
isocaloric treatment beverages, so it is not possible to completely discount the
potential effects of the additional calories in the CHO+ProH beverage. However,
the current study demonstrates that the ergogenic effects of CHO+ProH are
observed during time-trial protocols, even when ingested at very high (~60 g/hr)
levels of carbohydrate intake.
Only one prior study has compared CHO+Pro and CHO beverages using a
time-trial protocol. In contrast to the current findings, Van Essen and Gibala
(2006) observed no differences in performance between CHO+Pro (135 ± 9 min)
and CHO (135 ± 9 min) treatments during an 80-km time trial. In addition, time
splits for each 20-km segment of the trial were not different between treatments.
The reasons for the findings differing from those of the current study are unclear.
Figure 2 - Pre- and postexercise plasma creatine kinase (CK) levels and muscle-soreness
ratings, M ± SEM. CHO = carbohydrate; CHO+ProH = CHO plus casein hydrolysate; VAS
= visual analog scale. *Significantly higher (p < .05) than preexercise.
146 Saunders et al.
Apparently, Van Essen and Gibala’s protocol mimicked a flat time trial and did not
examine time differences for the latest stages of exercise, when the potential benefits
of performance from CHO+Pro beverages might be most apparent. As previously
discussed, the assessment of late-exercise performance in the current study
might have increased the sensitivity to detect treatment differences, especially
with a metabolically challenging climb occurring in the final 5 km of the trial.
The differing results between studies might have been influenced by the
sources of protein used in the beverages. The three prior studies reporting improved
endurance with CHO+Pro all used intact whey protein (Ivy et al., 2003; Saunders
et al., 2004, 2007). However, it is difficult to directly compare our results with
those studies because they each measured performance using time-to-exhaustion
protocols. The current investigation and the study of Van Essen and Gibala (2006)
both examined time-trial performance, and both used similarly high rates of fluid
(1,000 ml/hr), carbohydrate (60 g/hr), and protein (15-20 g/hr) compared with the
aforementioned studies (508-600 ml/hr, 37-47 g/hr, and 9-12 g/hr, respectively).
However, Van Essen and Gibala used intact whey protein, whereas the current
study used a casein protein hydrolysate.
It could be that Van Essen and Gibala (2006) failed to observe a performance
benefit from protein because there is a limited capacity to digest and absorb intact
proteins during prolonged endurance exercise. Grimble et al. (1986, 1987) compared
absorption rates of protein hydrolysates and their equivalent amino acid
mixtures using jejunal-perfusion techniques. Amino acids were more rapidly
absorbed from hydrolysates containing small peptides (Grimble et al., 1986,
1987), and the authors suggested that brush-border hydrolysis of peptides with
four or more amino acids limited the rate of absorption (Grimble et al., 1987). In
addition, ileal endogenous protein losses are higher after consumption of intact
protein or long-chain protein hydrolysates than protein hydrolysates containing
di- and tripeptides (Moughan, Fuller, Han, Kies, & Miner-Williams, 2007). Higher
endogenous losses result from increased production of digestive enzymes and
mucin and greater sloughing of intestinal-tract cells. The protein hydrolysate used
in the current study (PeptoPro) contained mainly di- and tripeptides and, in an
animal model, was shown to exhibit lower endogenous protein losses than its
native protein source, casein (Moughan et al.). As a consequence, more protein is
available for, for example, muscle synthesis.
As suggested earlier, hydrolysates containing di- and tripeptides might positively
influence amino acid absorption rates and lower endogenous protein production.
In addition, Fairclough, Hegarty, Silk, and Clark (1980) suggested that
small peptides might provide positive effects on water and electrolyte absorption
versus hydrolysates containing larger peptides. Thus, the use of di- and tripeptides
might have influenced the positive performance outcome observed in the current
investigation.
Including the current findings, four of the six studies examining CHO+Pro
ingestion during endurance exercise have reported performance benefits versus
CHO. The mechanisms by which CHO+Pro might promote improved endurance
are currently unknown. In a recent review of this topic (Saunders, 2007) various
potential mechanisms were discussed, including increased protein oxidation
(potentially sparing muscle glycogen), improved maintenance of TCA cycle intermediates,
attenuation of central fatigue, improved uptake of fluid or other fuel
CHO/Protein Hydrolysate and Time-Trial Performance 147
substrates, and augmented insulin stimulation. In addition, Betts, Williams,
Boobis, and Tsintzas (2008) recently reported that CHO+Pro consumed immediately
after a bout of prolonged treadmill running resulted in significant increases
in whole-body carbohydrate oxidation during a subsequent bout of exercise, without
alterations in muscle glycogen utilization. However, very few studies have
examined the influence of CHO+Pro consumption during exercise on these potential
mechanisms, and the metabolic influences of CHO+Pro ingestion related to
improved endurance performance remain poorly understood at present.
A secondary purpose of this study was to assess markers of muscle disruption
between CHO and CHO+ProH treatments. No significant differences were
observed in postexercise levels of plasma CK or ratings of muscle soreness
between treatments. However, both variables were significantly elevated from
preexercise to postexercise in the CHO trial but not in the CHO+ProH trial. Several
studies have reported that CHO+Pro ingestion during and/or after endurance
exercise might reduce postexercise plasma CK levels (Luden et al., 2007; Romano-
Ely
et al., 2006; Saunders et al., 2004; Valentine, Saunders, Todd, & St. Laurent,
2008) and ratings of muscle soreness (Flakoll, Judy, Flinn, Carr, & Flinn, 2004;
Luden et al.; Millard-Stafford et al., 2005; Romano-Ely et al.) compared with
CHO ingestion. These effects have been reported when CHO+Pro and CHO beverages
were matched for carbohydrate content (Luden et al.; Millard-Stafford et
al.; Saunders et al., 2004; Valentine et al.) or total calories (Romano-Ely et al.;
Valentine et al.). The absence of a significant treatment difference in the current
study might have been the result of differences in exercise protocols, in participant
samples, and in statistical power related to these varied factors. For example,
Luden et al. recently reported significant reductions in plasma CK levels with
CHO+Pro supplementation despite mean treatment differences that were very
similar to those of the current study. However, Luden et al. used a sample of 23
participants, providing the statistical power to observe more subtle differences
between treatments than the current investigation (Lipsey, 1990).
No studies to date have determined whether CHO+Pro ingestion during prolonged
exercise attenuates changes in myofibrillar muscle damage. Although
inferences regarding muscle damage might be made from changes in plasma CK
and muscle-soreness values, these measurements do not always correlate well
with direct measures of muscle damage (Beaton, Allan, Tarnopolsky, Tiidus, &
Phillips, 2002; Warren, Lowe, & Armstrong, 1999). However, changes in muscle
function might be the most relevant measure of muscle recovery for athletes. In a
recent investigation, Valentine et al. (2008) reported plasma CK values after
exhaustive cycling that were quite similar to those of the current study (373 ± 417
U/L after a CHO trial vs. 192 ± 149 U/L for CHO+Pro). This relatively small
attenuation in plasma CK was accompanied by significantly improved muscle
function 24 hr after exercise. Based on the findings of the current study alone, we
cannot clearly conclude a significant treatment effect on markers of muscle disruption.
However, the general trends of the data are consistent with other recent
studies of CHO+Pro ingestion and suggest that including protein in the beverage
might have provided a protective effect from muscle disruption after heavy
exercise.
In conclusion, ingesting a CHO+ProH beverage during endurance cycling
produced significant improvements in late-exercise time-trial performance
148 Saunders et al.
compared with a CHO beverage. These findings are particularly relevant for
athletes, because the beverages were matched at theoretically maximal levels of
exogenous carbohydrate oxidation (~60 g/hr), above which further performance
benefits would be unlikely with additional carbohydrate content. The magnitudes
of performance differences (3% during the final 5-km climb) were smaller than in
previous studies of CHO+Pro using time-to-exhaustion protocols but remain
highly important for competitive athletes.
CHO+ProH ingestion during and after a cycling time trial also prevented
increases in plasma CK and muscle-soreness ratings that were observed in the
CHO trial. These findings support previous research suggesting that CHO+ProH
beverages consumed during and immediately after exercise might be advantageous
for performance and muscle recovery in endurance athletes.
Acknowledgments
The authors wish to thank DSM Food Specialties, Inc., Delft, The Netherlands, for
supporting this project with a research grant. Dr. Arie Kies is an employee of DSM Food
Specialties. In addition, the authors are grateful to David Bolton, Adam Clawson, Brian
McCarthy, Jamie Munnis, and Melissa Rivers for their assistance with data collection and
to Dr. Wim Plugge (DSM Food Specialties) for statistical advice.
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