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Acute milk-based protein–CHO supplementation
attenuates exercise-induced muscle damage
Emma Cockburn, Philip R. Hayes, Duncan N. French, Emma Stevenson, and
Alan St Clair Gibson
Abstract: Exercise-induced muscle damage (EIMD) leads to the degradation of protein structures within the muscle. This
may subsequently lead to decrements in muscle performance and increases in intramuscular enzymes and delayed-onset
muscle soreness (DOMS). Milk, which provides protein and carbohydrate (CHO), may lead to the attenuation of protein
degradation and (or) an increase in protein synthesis that would limit the consequential effects of EIMD. This study exam-
ined the effects of acute milk and milk-based protein–CHO (CHO-P) supplementation on attenuating EIMD. Four inde-
pendent groups of 6 healthy males consumed water (CON), CHO sports drink, milk-based CHO-P or milk (M), post
EIMD. DOMS, isokinetic muscle performance, creatine kinase (CK), and myoglobin (Mb) were assessed immediately be-
fore and 24 and 48 h after EIMD. DOMS was not significantly different (p> 0.05) between groups at any time point.
Peak torque (dominant) was significantly higher (p< 0.05) 48 h after CHO-P compared with CHO and CON, and M com-
pared with CHO. Total work of the set (dominant) was significantly higher (p< 0.05) 48 h after CHO-P and M compared
with CHO and CON. CK was significantly lower (p< 0.05) 48 h after CHO-P and M compared with CHO. Mb was sig-
nificantly lower (p< 0.05) 48 h after CHO-P compared with CHO. At 48 h post-EIMD, milk and milk-based protein–
CHO supplementation resulted in the attenuation of decreases in isokinetic muscle performance and increases in CK and
Mb.
Key words: isokinetic performance, DOMS, creatine kinase, myoglobin, sports drinks, eccentric exercise.
Re
´sume
´:Les le
´sions musculaires cause
´es par l’exercice (EIMD) entraı
ˆnent la de
´gradation des structures prote
´iques dans
la fibre musculaire. Cette de
´gradation peut conduire a
`la diminution de la performance musculaire et a
`l’augmentation de
la concentration des enzymes intramusculaires et des courbatures (DOMS). Le lait, source de prote
´ines et de glucides
(CHO), contribuerait a
`l’atte
´nuation de la de
´gradation prote
´ique et a
`l’augmentation de la synthe
`se prote
´ique et, de ce fait,
diminuerait les effets des EIMD. Cette e
´tude se propose donc d’analyser les effets de la consommation de lait et de sup-
ple
´ments de prote
´ines et de glucides lacte
´s (CHO-P) sur l’atte
´nuation des EIMD. Quatre groupes inde
´pendants constitue
´s
de 6 hommes en bonne sante
´consomment de l’eau (CON), une boisson e
´nerge
´tique sucre
´e, des prote
´ines et des glucides
lacte
´s (CHO-P) ou du lait (M), et ce, a
`la suite d’EIMD. Imme
´diatement avant les EIMD, puis 24 h et 48 h apre
`s, on e
´va-
lue les DOMS, la performance musculaire isocine
´tique, et les concentrations de cre
´atine kinase (CK) et de myoglobine
(Mb). D’un groupe a
`l’autre et d’un moment a
`l’autre, on n’observe pas de diffe
´rence de perception des DOMS (p>
0,05). Comparativement aux groupes CHO et CON, le moment de force de pointe du co
ˆte
´dominant du groupe CHO-P est
significativement plus important 48 h apre
`s la supple
´mentation (p< 0,05); on observe le me
ˆme phe
´nome
`ne chez le groupe
M comparativement au groupe CHO. La quantite
´totale de travail effectue
´du co
ˆte
´dominant durant la se
´rie d’exercices est
aussi significativement plus importante (p< 0,05) 48 h apre
`s la supple
´mentation en CHO-P et apre
`s la consommation de
M, comparativement a
`CHO et a
`CON. Comparativement a
`CHO, la concentration de CK 48 h apre
`s la supple
´mentation
en CHO-P et la consommation de M est significativement moins importante (p< 0,05). Comparativement a
`CHO, la
concentration de Mb est aussi significativement plus faible 48 h apre
`s la supple
´mentation en CHO-P (p< 0,05). Quarante-
huit heures apre
`s les EIMD, la consommation de lait et de supple
´ments de prote
´ines et de glucides lacte
´s atte
´nue la dimi-
nution de performance musculaire isocine
´tique et l’augmentation des concentrations de CK et de Mb.
Mots-cle
´s:performance isocine
´tique, DOMS, courbatures, cre
´atine kinase, myoglobine, boisson e
´nerge
´tique, excentrique.
[Traduit par la Re
´daction]
Introduction
Exercise-induced muscle damage (EIMD) has been shown
to be caused by activities involving eccentric muscle actions
(Byrne and Eston 2002a, 2002b; Harrison and Gaffney
2004; Semark et al. 1999; Twist and Eston 2005). EIMD
has a number of consequential effects including delayed on-
set of muscle soreness (DOMS) (MacIntyre et al. 2001;
Nosaka et al. 2002; Semark et al. 1999), increased release
of intramuscular enzymes into the plasma (Clarkson et al.
Received 4 December 2007. Accepted 30 April 2008. Published
on the NRC Research Press Web site at apnm.nrc.ca on 4 July
2008.
E. Cockburn,1P.R. Hayes, E. Stevenson, and
A. St Clair Gibson. Division of Sports Sciences, Northumbria
University, Newcastle, UK.
D.N. French. English Institute of Sport – North East, Gateshead,
UK.
1Corresponding author (e-mail: e.cockburn@unn.ac.uk).
775
Appl. Physiol. Nutr. Metab. 33: 775–783 (2008) doi:10.1139/H08-057 #2008 NRC Canada
1986; Seifert et al. 2005; Sorichter et al. 2001) and most im-
portantly, in terms of sport performance, decrements in
muscle performance (Byrne and Eston 2002a, 2002b;
Harrison and Gaffney 2004; Twist and Eston 2005).
Disruption of force-generating and (or) force-transmitting
structures is thought to be one of the main mechanisms re-
sponsible for the decrements in muscle performance occur-
ring in the days following muscle-damaging exercise
(Warren et al. 2001). Changes in protein metabolism
(Fielding et al. 1991) have been suggested as a causal factor
of the ultrastructural damage observed following muscle-
damaging exercise.
Nutritional supplements may minimize changes in protein
metabolism rather than the initial mechanical event
(Bloomer and Goldfarb 2003). A combination of protein
and carbohydrate (CHO) has been found to be optimal for
eliciting a positive effect on protein balance. (Biolo et al.
1997; Bird et al. 2006; Elliot et al. 2006; Miller et al. 2003;
Rasmussen et al. 2000). Therefore, the consumption of a
protein–CHO (CHO-P) supplement may attenuate decre-
ments in muscle performance, and increases in intramuscular
enzymes, and DOMS.
CHO-P supplements have been shown to attenuate EIMD
more than CHO and placebo solutions (Baty et al. 2007;
Cade et al. 1991; Koller 2005; Ready et al. 1999; Saunders
et al. 2004; Seifert et al. 2005). However, these studies
have based their conclusions on measures of intramuscular
enzymes only (creatine kinase (CK) and myoglobin (Mb)).
From a practical perspective it may be more important and
relevant to investigate the effects on muscle performance.
Studies that have measured muscle performance following
EIMD and observed beneficial effects have used prolonged
supplementation of amino acids (Ratamess et al. 2003;
Sugita et al. 2003). However, the only study known to date
that has used measures of muscle performance along with
other indicators of EIMD found no beneficial effect of
acute supplementation with a CHO-P drink (Wojcik et al.
2001).
The evidence for CHO-P supplements attenuating EIMD
has been contradictory. Furthermore, it is apparent that there
is limited research using muscle performance as an indirect
marker of EIMD, which from an applied perspective is cru-
cial to investigate. The majority of the research in the area
of CHO-P drinks and muscle damage has not used milk-
based drinks. Milk and milk-based drinks are readily avail-
able and are a high-quality, inexpensive (Wojcik et al.
2001) source of amino acids that result in a positive protein
balance after resistance exercise (Elliot et al. 2006). The
benefits of consuming milk-based drinks in other areas of
sport nutrition has been investigated (Karp et al. 2006;
Shirreffs et al. 2007; Wojcik et al. 2001). Previously, studies
in the field of EIMD and nutritional interventions comparing
CHO-P and CHO drinks have matched for energy intake
(Wojcik et al. 2001) or CHO content (Luden et al. 2007;
Saunders et al. 2004). This study compared commercially
available drinks in volumes that athletes could realistically
consume post exercise, which is similar to Ready et al.
(1999). The aim of this study was to investigate the use of
commercially available milk and milk-based CHO-P supple-
ments in attenuating EIMD following resistance-based ec-
centric exercise.
Materials and methods
Participants
Twenty-four healthy male participants (age 21 ± 3 years;
height 180.8 ± 5.7 cm; mass 80.2 ± 9.1kg) who regularly
competed in team sports (football, rugby, hockey and
cricket) volunteered to take part in the study. After institu-
tional ethical approval was obtained, the experimental pro-
cedures, associated risks, and benefits were explained
before participants gave their written informed consent. Par-
ticipants were fully familiarized with all testing procedures
prior to commencing the study. Participants were instructed
to maintain their habitual diet throughout and arrive at the
laboratory in a rested state, having avoided strenuous physi-
cal activity for at least 48 h and not taken any nutritional
supplements, caffeine, alcohol, or anti-inflammatory drugs.
Participants were tested at approximately the same time of
day to minimize diurnal variation.
Procedures
Design
Participants were assigned to 1 of 4 independent groups,
which were single blinded. Participants were equally
matched into groups based on concentric knee flexion peak
torque recorded from 6 leg extension–flexions during pre-
liminary testing. The groups were allocated 1 of 4 nutri-
tional supplements: (i) milk-based CHO-P, (ii) milk (M),
(iii) CHO, or (iv) water (CON). A one-way analysis of var-
iance revealed no group differences in baseline subject char-
acteristics (p> 0.05). There were no significant differences
between groups in peak torque values used for group alloca-
tion (p> 0.05).
All participants were required to attend the laboratory on
3 consecutive days. Before the initial tests on day 1, height
and mass were recorded. On each day prior to any exercise
and following a 10 min rest, a venous blood sample was col-
lected for analysis. Following this, participants rated their
level of muscle soreness on a visual analogue scale (Close
et al. 2004), completed a standardized warm-up, and carried
out isokinetic muscle performance measures. On day 1, fol-
lowing all other measures and after a rest period of ~10 min,
participants completed a bout of exercise designed to induce
acute muscle damage. Upon completing the exercise bout
they immediately consumed 500 mL of their allocated nutri-
tional supplement and again within 2 h post muscle-
damaging exercise. At 24 and 48 h post-exercise participants
had a venous blood sample collected, rated their level of
muscle soreness, completed a standardized warm-up, and
carried out isokinetic muscle performance measures only.
Nutritional supplements
The nutritional content of each drink is shown in Table 1.
The CHO-P supplement was a commercially available low-
fat chocolate milkshake designed to facilitate an athlete’s
recovery following exercise (For Goodness Shakes, My
Goodness Ltd., London, UK). This product provided protein
in the form of semi-skimmed milk and CHO in the forms of
lactose, sucrose, fructose, maltodextrin, and cellulose. The
M supplement was semi-skimmed (Rock Farm Dairy, Dur-
ham, UK) and provided CHO in the form of lactose. The
776 Appl. Physiol. Nutr. Metab. Vol. 33, 2008
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2008 NRC Canada
CHO supplement was a commercially available sports drink
(Lucozade Sport, GlaxoSmithKline, UK) providing CHO in
the form of glucose and maltodextrin. Drink content was
not standardized, as part of the purpose of this study was to
use commercially available drinks. Each supplement is com-
mercially available in 500 mL bottles, therefore participants
were provided with 2 standard servings (1000 mL).
Muscle-damaging exercise
Muscle damage was induced in the hamstrings. Partici-
pants completed 6 sets of 10 repetitions of unilateral
eccentric–concentric actions of the knee flexors at a test
speed of 1.05 rads–1 using a Cybex Isokinetic Dynamometer
(Cybex Norm, Cybex International, New York, N.Y.). A rest
period of 90 s was given between sets on one side of the
body and ~4 min was given to adjust the equipment before
conducting the same assessment on the contralateral leg.
Participants were instructed to provide a maximal effort dur-
ing the eccentric phase of each leg flexion. During the con-
centric phase, participants were instructed to return their leg
to the starting position with minimum effort. Pilot testing
demonstrated that this protocol, which was adapted from
previous research (Harrison and Gaffney 2004), resulted in
EIMD of the hamstrings (i.e., increased CK and decreased
isokinetic muscle performance). Previous studies have used
the non-dominant limb (Sayers and Clarkson 2001; Sayers
et al. 2000) or have not specified the use of the dominant
or non-dominant limb (Bowers et al. 2004; Cleak and Eston
1992; Harrison and Gaffney 2004; Howell et al. 1993;
Rodenburg et al. 1993), assuming that both limbs respond
similarly. To the best of our knowledge this assumption has
not been investigated, therefore both legs were tested in this
protocol.
DOMS measurement
The degree of DOMS experienced was measured on a vis-
ual analogue scale. Participants were required to rate the
level of soreness, combined for both legs, that they per-
ceived to have in their hamstrings when standing from 0
(no pain–soreness) up to 10 (pain–soreness as bad as it
could be). Using similar scales, previous investigators have
shown significant increases in DOMS following EIMD
(Close et al. 2004; Semark et al. 1999; Twist and Eston
2005).
Measures of isokinetic muscle performance
Peak torque of the best repetition and total work of the set
for 6 concentric maximal-effort knee flexion repetitions
were measured sequentially on both legs at a test speed of
1.05 rads–1 using a Cybex Isokinetic Dynamometer (Cybex
Norm). Participants were required to maximally extend and
flex their leg over their maximum range of motion (ROM)
for 6 repetitions. Approximately 4 min was given to adjust
the equipment before conducting the same assessment on
the contralateral leg.
Blood sample collection and analysis
Serum CK and Mb concentrations were determined from
blood samples collected via venipuncture from a forearm
vein into a serum gel monovette (4.9 mL). The samples
were centrifuged at 3000 rmin–1 for 10 min (Allegra X-22
Centrifuge, Beckman Coulter, Bucks, UK). Thirty micro-
litres of the resulting serum was alliquoted and used for the
immediate analysis of CK (Reflotron Plus System, Bio-Stat
Diagnostic Systems, Stockport, UK). The remaining serum
was removed and stored at –20 8C for later analysis of Mb
(Myoglobin Enzyme Immunoassay Test Kit, Oxford Bio-
systems Ltd., Wheatley, Oxon, UK). Absorbance was read
using an Anthos 2010 Microplate reader (Anthos Labtec In-
struments, Salzberg, Germany).
Intra-assay and inter-assay coefficients of variation (CVs)
for CK were 3.5% and 3.7%, respectively. For Mb assays,
they were 3.9%–6.6% and 5.2%–11.8%, respectively.
Data analysis
Results are presented as means and standard error of the
mean. Mauchley’s test was used to check the sphericity of
the data. Differences in isokinetic muscle performance meas-
ures were determined using a factorial analysis of variance
(ANOVA) with repeated measures on 2 factors (day and
leg). Differences in CK, Mb, and DOMS were determined
using a factorial ANOVA with repeated measures on 1 factor
(day). Differences between groups in changes from baseline
at 24 and 48 h for each variable were analysed using one-
way ANOVAs. Significant within effects were analyzed
using Bonferonni step-wise calculation (Field 2005). Signifi-
cant between effects were analysed using a Games Howell
post-hoc test (Field 2005). Significant interaction effects
were analyzed using Tukey’s honestly significant difference
(HSD) test. Statistical significance was set at p< 0.05.
Results
Evidence of muscle damage
For all subjects the protocol was deemed to have caused
EIMD in both legs. This was evident from reductions in iso-
kinetic muscle performance and increases in CK, Mb, and
DOMS over the 3 days of testing (Table 2).
Effects of nutritional supplement
DOMS
No significant differences between groups (F3, 20 = 2.617,
p= 0.079) or significant interaction effects between day and
group (F6, 40 = 1.323, p= 0.270) were observed for DOMS
(Fig. 1).
Isokinetic muscle performance
Peak torque
A significant main effect for leg (F1, 18 = 22.115, p<
0.001) and a significant leg group interaction (F3, 18 =
5.397, p= 0.008) were found for peak torque.
There were significant decreases of peak torque for the
Table 1. Nutritional content of commercially
available beverages used in this study.
Supplement Energy
(kcal) Protein
(g) CHO
(g) Fat
(g)
CHO-P 706.8 33.4 118.2 16.4
M 480 34 49.17
CHO 280 Trace 64.Trace
Cockburn et al. 777
#
2008 NRC Canada
dominant leg between 0 and 48 h in the CON group only.
Post hoc tests demonstrated that for the dominant leg, peak
torque was significantly higher after 48 h in the CHO-P
group compared with the CON and CHO groups, and in the
M group compared with the CHO group (Fig. 2).
There were significant decreases of peak torque for the
non-dominant leg between 0 and 48 h in the CON group
only. Post hoc tests demonstrated that for the non-dominant
leg, peak torque was significantly higher at 48 h in the
CHO-P and M groups than in the CON group.
Total work of the set
A significant main effect for leg (F1, 18 = 30.645, p<
0.001) and significant leg group interaction (F3, 18 =
7.010, p= 0.003) were found for total work of the set.
There were significant decreases in total work of the set
Table 2. Muscle soreness, blood markers, and isokinetic muscle performance following exercise-induced muscle damage.
Time
(h) DOMS
(cm) Creatine kinase
(UL–1)Myoglobin
(ngmL–1)
Peak torque
dominant
(Nm)
Peak torque
non-dominant
(Nm)
Total work of
set dominant
(J)
Total work of set
non-dominant
(J)
0.0.7±0.2 96.6±18.7 55.14±14.84 123.±3 118±3 981.±28 920.±31
24.5.1±0.4a331.8±65.7a240.56±68.73a115.±5 101±4a798.±41a718.±35a
48.7.1±0.4b539.1±104.4b331.80±82.68a100.±7b90±6b681.±61b608.±53b
aSignificantly different from 0 h (p< 0.05).
bSignificantly different from 0 and 24 h (p< 0.05).
Fig. 1. Muscle soreness response to exercise-induced muscle damage in the M (n= 6), CHO-P (n= 6), CHO (n= 6), and CON (n=6)
groups. No significant differences were observed (p> 0.05). CHO, carbohydrate; CHO-P, protein–CHO; CON, water; M, milk.
Fig. 2. Peak torque of the dominant leg in response to exercise-induced muscle damage in the M (n= 5), CHO-P (n= 6), CHO (n= 6), and
CON (n= 5) groups. *, significantly different from 0 h (p< 0.05); {, significantly different from CON (p< 0.05); §, significantly different
from CHO (p< 0.05). CHO, carbohydrate; CHO-P, protein–CHO; CON, water; M, milk.
778 Appl. Physiol. Nutr. Metab. Vol. 33, 2008
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2008 NRC Canada
within days for the dominant leg in the CON (0–24 h and 0–
48 h), CHO (24–48 h and 0–48 h), M (0–48 h), and CHO-P
(0–48 h) groups. Post hoc tests revealed that for the domi-
nant leg, total work of the set at 48 h was significantly
higher in the CHO-P and M groups than in the CHO and
CON groups (Fig. 3).
There were significant decreases in total work of the set
within days for the non-dominant leg in the CON (0–24 h
and 0–48 h), CHO (0–48 h and 24–48 h), M (0–24 h and
0–48 h), and CHO-P (0–24 h and 0–48 h) groups. Post hoc
tests revealed that for the non-dominant leg, total work of
the set at 48 h was significantly higher in the CHO-P group
than in the CON group.
Blood markers
CK analysis identified no significant main effect for
groups (F3, 18 = 2.093, p= 0.137). A significant day group
interaction effect over the 3 days of testing (F6, 36 = 3.124,
p= 0.014) was observed for CK. Post-hoc tests revealed sig-
nificantly lower CK values at 48 h in the M and CHO-P
groups than in the CHO group (Fig. 4). CK concentrations
significantly increased from 0 h to 48 h in the CON and
CHO groups only. Significant increases in CK were ob-
served between 24 and 48 h for the CHO group only.
A significant main effect for group (F3, 18 = 3.399, p=
0.040) was found for Mb. Post-hoc tests revealed that Mb
concentrations in the M and CHO-P groups were signifi-
cantly lower than in the CHO group (Fig. 5). Running a
one-way ANOVA for changes in baseline after 48 h re-
vealed a significant effect for group (F3, 18 = 3.628, p=
0.033). Post hoc tests revealed that Mb concentration in the
CHO-P group was significantly lower than in the CHO
group (p< 0.05).
Discussion
The primary finding of this study indicated that milk and
milk-based protein–CHO supplementation attenuated peak
torque, total work of the set, CK, and Mb 48 h after
muscle-damaging exercise. There were no beneficial effects
Fig. 3. Total work of the set of the dominant leg in response to exercise-induced muscle damage in the M (n= 5), CHO-P (n= 6), CHO
(n= 6), and CON (n= 5) groups. *, significantly different from 0 h (p< 0.05); {, significantly different from 0 and 24 h (p< 0.05); {,
significantly different from CON (p< 0.05); §, significantly different from CHO (p< 0.05). CHO, carbohydrate; CHO-P, protein–CHO;
CON, water; M, milk.
Fig. 4. CK response to exercise-induced muscle damage in the M (n= 6), CHO-P (n= 6), CHO (n= 4), and CON (n= 6) groups. *,
significantly different from 0 h (p< 0.05); {, significantly different from 0 and 24 h (p< 0.05); §, significantly different from CHO (p<
0.05). CHO, carbohydrate; CHO-P, protein–CHO; CK, creatine kinase; CON, water; M, milk.
Cockburn et al. 779
#
2008 NRC Canada
of consuming milk or milk-based protein–CHO on percep-
tions of muscle soreness.
The intake of protein + CHO may have lead to the attenu-
ation of EIMD by altering protein metabolism. Protein
intake will increase amino acid availability (Tipton and
Wolfe 2001) and CHO will provide the optimal hormonal
environment by increasing insulin (Borsheim et al. 2004;
Miller et al. 2003). Together they will subsequently increase
protein synthesis (Biolo et al. 1997; Elliot et al. 2006; Miller
et al. 2003; Rasmussen et al. 2000; Roy et al. 2000; Wolfe
2001) and there may be no concomitant increases in protein
breakdown (Bird et al. 2006). In support of this it has been
shown that muscle protein synthesis is increased post eccen-
tric exercise in the context of hyperaminoacidemia (Moore
et al. 2005).
Changes in protein metabolism may have lead to the at-
tenuation of ultrastructural damage. As a consequence, myo-
fibrillar disruption, contractile protein loss and cell
membrane integrity would be better maintained. Following
resistance exercise myofibrillar protein is maintained with
the consumption of a protein–CHO supplement (Bird et al.
2006). This would subsequently lead to attenuation of peak
torque, total work of the set, CK, and Mb. To our knowl-
edge a direct relationship between muscle performance and
changes in protein metabolism has not been observed in the
literature; however, this is plausible. A relationship between
muscle performance and the percentage of desmin-negative
fibres has previously been observed (Lieber et al. 1994). It
is possible that fibres lacking desmin have undergone a de-
gree of proteolysis (Lieber et al. 1994). This explanation is
in agreement with other studies who have found beneficial
effects of protein–CHO ingestion (Cade et al. 1991; Ready
et al. 1999; Saunders et al. 2004).
There were no significant differences in the results be-
tween M and CHO-P in isokinetic muscle performance, CK,
or Mb. Both of these nutritional supplements contained sim-
ilar amounts of protein. Thus any effect on attenuating
EIMD based on protein ingestion would be similar for both
groups. The M and CHO-P supplements did differ in terms
of CHO content with CHO-P containing approximately 2.5
times more CHO. CHO increases insulin (Borsheim et al.
2004; Miller et al. 2003), which has been shown to increase
muscle amino acid uptake and synthesis and reduce protein
degradation (Ivy 2004). Previous research has indicated that
as little as 35 g of sucrose in combination with 6 g of amino
acids will promote muscle anabolism (Rasmussen et al.
2000; Tipton et al. 2001). Both the M and CHO-P supple-
ments had a greater amount of CHO than this. There may
be a ceiling effect to CHO content; therefore, any effect of
CHO on protein metabolism may have been similar for both
supplements. In addition, the different CHO solutions in
each of the drinks may have affected postprandial insulin re-
sponse, which may have influenced protein metabolism.
However, a previous study indicated that postprandial insu-
lin response was not significantly different between different
CHO solutions co-ingested with protein post resistance exer-
cise (Kreider et al. 2007). Therefore, the different CHO sol-
utions would not appear to affect protein metabolism and
thus the attenuation of EIMD differently. Furthermore, Bird
et al. (2006) have indicated that insulin does not play a role
in the regulation of myofibrillar protein degradation. This
may explain why there were no differences between the 2
groups in the measured variables.
The attenuation of EIMD following M and CHO-P
supplementation was not apparent until 48 h after muscle-
damaging exercise. Ultrastructural damage becomes pro-
gressively worse in the days following eccentric exercise,
with more damage being observed during 24–48 h after
exercise (Newham et al. 1983) or 3 days later (Friden et
al. 1983). This may partly be because protein degradation
rates do not increase until 24 h later (Lowe et al. 1995;
Wojcik et al. 2001), peaking at 48 h (Lowe et al. 1995).
During this time of increased degradation, protein synthesis
rates remain below baseline (Lowe et al. 1995). Overall,
protein balance would remain negative. This may imply
that changes in the measured variables before 48 h are not
due to ultrastructural damage via protein degradation but to
other processes that may be mechanical in nature. In sup-
port of this, urinary 3-methylhistidine excretion is not sig-
nificantly reduced until 48 h after resistance exercise with
the consumption of a CHO-essential amino acid supplement
(Bird et al. 2006). This may be why, in the present study,
Fig. 5. Mb response to exercise-induced muscle damage in the M (n= 6), CHO-P (n= 6), CHO (n= 4), and CON (n= 6) groups. §,
significantly different from CHO (p< 0.05). CHO, carbohydrate; CHO-P, protein–CHO; CON, water; M, milk; Mb, myoglobin.
780 Appl. Physiol. Nutr. Metab. Vol. 33, 2008
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2008 NRC Canada
the attenuation of EIMD was not observed until 48 h after
muscle-damaging exercise.
Attenuations of CK and Mb are in agreement with pre-
vious work (Cade et al. 1991; Ratamess et al. 2003; Ready
et al. 1999; Saunders et al. 2004; Seifert et al. 2005; Sugita
et al. 2003). However, to our knowledge, this is the first
study that has demonstrated attenuated peak torque, total
work of the set, CK, and Mb following acute milk and
milk-based protein–CHO consumption when EIMD was in-
duced by resistance exercise. A similar study previously
conducted found no beneficial effects of protein–CHO in-
gestion on a number of measures of EIMD including iso-
kinetic muscle performance (Wojcik et al. 2001). This was
in the context of increased protein breakdown due to eccen-
tric exercise. They stated that only modest damage was in-
duced (Wojcik et al. 2001). This may indicate that our trial
resulted in greater changes in CK, DOMS, and isokinetic
muscle performance, which may explain the differences
found.
It was apparent that M and CHO-P had no significant ef-
fects on DOMS. It has been suggested that functional and
biochemical measures are preferred when comparing group
differences in EIMD (Rodenburg et al. 1993). DOMS is sub-
jective (Rodenburg et al. 1993), which may be the reason
for no observed differences between groups. EIMD was
only induced in the hamstrings. The hamstrings are only a
small muscle group in relation to the whole body, which
may have effected individual perceptions of DOMS.
The results indicate that the intake of CHO alone had no
beneficial effect on attenuating EIMD. This is partly in
agreement with Dalton et al. (1999) who found CHO intake
had no beneficial effect on EIMD as indicated by measure-
ments of CK. This is an interesting finding, as athletes tradi-
tionally consume CHO when recovering from exercise
(Millard-Stafford et al. 2005). This indicates that athletes
may be better off consuming milk or a milk-based protein–
CHO supplement after eccentric exercise. It is interesting to
note that based on CK and Mb data, CHO consumption ap-
peared to exacerbate the damage. However, it has previously
been stated that differences in CK levels do not provide in-
formation on the differences in the magnitude of EIMD
(Friden and Lieber 2001).
Participants were required to maintain their normal diet to
replicate free living. The limitation of this is that diet was
not strictly controlled. However, it would be expected that
participants with high protein intake would be equally dis-
tributed across groups. Furthermore, both groups consuming
protein and CHO demonstrated similar patterns of results.
This would be unlikely if participants with high habitual
protein intakes were allocated into one group.
In this study, a combination of protein and CHO appears
to be the key nutritional factor for attenuating EIMD. The
results indicate that an athlete may benefit from milk or a
milk-based protein–CHO drink. This would apply to athletes
starting on a new training programme involving a high
component of eccentric exercise or those increasing training
intensity of exercise involving eccentric muscle actions. It
would allow for subsequent training and competing to be
performed at a closer to optimal level and may lead to
hastened recovery, although further research is required to
clarify this.
In conclusion, milk and milk-based protein–CHO drinks
consumed immediately after resistance-based eccentric
muscle-damaging exercise lead to the attenuation of EIMD
48 h later. This may be due to altered protein metabolism
attenuating the disruption of muscle protein structures and
thus changes in peak torque, total work of the set, CK, and
Mb. There were no significant differences between these
groups. A future comparative study is required where treat-
ments are provided on an equicaloric basis and matched for
macronutrient composition to make unequivocal conclusions
on the value of one treatment over the others.
Acknowledgements
My Goodness Ltd. provided the CHO–protein product. No
finance was provided for conducting the study.
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