CAPÍTULO 3: RESUMEN Y ANÁLISIS DE LAS PROPUESTAS DE ENSEÑANZA
3.3 CLASSROOM NOTES: TEACHING THE CALCULUS
Individuals
5.0 INTRODUCTION
Dietary proteins, in particular branched chain amino acids (BCAA) have an important
role in regulating protein metabolism in skeletal muscle (Evans, 2001; Borsheim et al.,
2002; Karlsson et al., 2004). Eccentric exercise produces ultrastructural changes that
stimulate muscle protein synthesis and degradation. Protein degradation usually exceeds
synthesis and thus a negative protein balance is created, resulting in net muscle protein
breakdown and muscle degeneration (Evans, 2001).
Furthermore, within hours of injury, the number of circulating neutrophils can be
increased dramatically. Neutrophils migrate to the site of injury where they phagocytize
tissue debris and release factors such as lysozymes and oxygen radicals, which also
contribute to the increased breakdown and degradation of muscle contractile proteins
(Evans, 1986). Taken together, these changes can lead to measurable indirect markers of
exercise-induced muscle damage including reduced muscle strength (maximum
voluntary contraction; MVC), muscle soreness (DOMS), and release of myocellular
proteins such as CK and LDH into the plasma (Nosaka et al., 2000; Friden and Lieber,
2001).
Following eccentric exercise-induced damage, muscle regeneration induces local
accumulation of several peptide growth factors, including insulin like growth factor
(IGF-I) (Yan et al., 1993), fibroblast growth factor (FGF) (Yamada et al., 1989), and
satellite cell proliferation. Satellite cells are involved in the process of repairing injured
muscle fibres, and subsequent formation of new muscle cells in vivo; all processes
which require an enhanced rate of protein synthesis (Evans. 2001).
Therefore, a nutritional supplement that can achieve a positive net muscle protein balance is likely to increase the rate of protein synthesis, satellite cell proliferation, and thus improve muscle fibre regeneration. Indeed, Tipton et al. (1999) and more recently Borsheim (2002), have shown that net muscle protein balance is negative post-exercise when individuals are maintained in the post-absorptive state during recovery. In contrast, those who ingested protein had a positive protein balance.
There is evidence to suggest that compared to regular protein supplements, whey isolate
is more effective at increasing blood amino acids and protein synthesis due to its
different absorption kinetics and amino acid profile (Mahe et al., 1996; Bucci and Unlu,
2000). Hydrolysed whey proteins are rapidly absorbed in the upper jejunum (Mahe et
al., 1996) and contain the highest concentration of the essential amino acids, including
BCAA’s (Bucci and Unlu, 2000). Furthermore, whey protein exhibits the highest
biological value (BV) of any known protein (Renner, 1983). Whey protein has a BV
score of 104 whereas casein, another milk protein, beef and fish have BV scores of 77,
75, and 75, respectively (Renner, 1983). Biological value is the measure of the protein’s
ability to retain nitrogen in the muscle (Colgan, 1993), and a positive nitrogen balance
is associated with muscle anabolism (protein synthesis).
Thus, the purpose of this study was to examine the effects of short-term consumption of
dietary supplement whey protein on muscle proteins and force recovery after
following eccentrically-induced damage: loss of muscle strength will be restored earlier;
and release of muscle proteins will be decreased, indicative of reduced damage and/or
faster recovery following whey protein supplementation.
5.1 METHODS
5.1.1 Participants
Seventeen healthy untrained males volunteered for this study. Subjects were generally
students of Victoria University. Descriptive characteristics of the subjects are presented
in table 5. Subjects were (a) non-smokers; (b) had not participated in resistance-training
for at least six months; and (c) had not ingested any ergogenic supplement for a 24-
week period prior to the start of supplementation. All participants were informed
verbally, as well as in writing, as to the objectives of the experiments, together with the
potential associated risks. All participants signed an informed consent document
approved by the Human Research Ethics Committee of Victoria University of Australia.
All procedures conformed to National Health and Medical Research Council guidelines
for the involvement of human subjects for research.
5.1.2 Dietary Supplementation.
Subjects were randomised in a double-blind placebo-controlled fashion into 2 groups:
an isocaloric carbohydrate placebo group (n= 8); and whey protein-supplemented group
(n= 9). The supplements were provided to participants in identical, unmarked, sealed
containers. The macronutrient content of the supplements was as follows; approx.
90gms protein, 8gms isocaloric carbohydrate, 2gms fat/100gms for Whey protein
supplement (VP2™ Hydrolyzed Whey Isolate) and 100gms isocaloric
carbohydrate/100gms for placebo control. Supplements were supplied by AST Sports
separate occasions (Naturalac Nutrition LTD, Level 2/18 Normanby Rd Mt Eden, New
Zealand) and met label ingredients on both occasions. Subjects were instructed to
consume 1.5 grams of either the supplement or placebo per kilogram of body weight for
a period of 14 days following a resistance exercise session, while maintaining their
habitual daily diet. Resistance-trained athletes widely use protein supplements to
achieve high protein intakes (Marquart et al., 1998). Therefore, we chose a supplement
dose that was characteristic of this population (Marquart et al., 1998), even though the
participants in this study were untrained individuals.
Subjects were advised to mix the supplement in water and consume the required dosage
in 3 equal serves over the period of the day, i.e. breakfast, lunch and dinner, 1 hour
before eating. Nutritional intake was monitored via written dietary diary sheet. Subjects
were instructed to record their nutrient intake for a 7-day period. All recordings were
assessed using Nutritionist PRO (First Data Bank) software.
5.1.3 Isokinetic/Isometric Strength and Vertical (Countermovement) Jump Measurements
Muscle strength and performance measurements were examined by voluntary isokinetic
knee flexion and isokinetic/isometric knee extension using the Cybex NormTm Testing
and Rehabilitation System and a vertical jump (CMJ) performed on a custom-built
strain gauge force platform (as previously described in section 3.1.3.1 & 3.1.3.2). All
strength and performance measurements were performed prior to- and immediately
following the exercise session, and on day 1, 2, 3, 4, 7, 10 and 14 post-exercise. It
should be noted that muscle strength values of the exercised leg, performed on the
Cybex NormTm Testing and Rehabilitation System, were expressed as percentage of pre-
performance were expressed as a percentage change from pre-exercise values. Previous
research has shown this to be a successful means of reporting muscle strength and
performance data (Rinard et al., 1999; Byrne and Eston. 2001).
5.1.4 Blood Sampling and Analysis
Blood was sampled from the antecubital fossa vein prior to and 30 min, 1, 2, and 4
hours following, the resistance exercise session and on days 1, 2, 3, 4, 7, 10 and 14 post
exercise. Blood was immediately placed into EDTA tubes and centrifuged at 3000 rpm
for 15 min at 4oC (as previously described in section 3.1.5). Plasma was stored at -80oC
for subsequent analysis of CK and LDH activity.
5.1.5 Statistical Analysis
Subject characteristics are reported as means ± SD. All other values are reported as
means ± SE. Statistical evaluation of data was accomplished by using a two-way
analysis of variance (ANOVA) with one between groups factor (supplement) and one
repeated factor (time), with subsequent Tukey’s Post-Hoc analysis. Where an
interaction was found, the location of the difference was determined by a students t-test.
Difference in participant characteristics and dietary analysis between groups was
assessed by students’ t-test. A P value of less then 0.05 was accepted for statistical
5.2 RESULTS
5.2.1 Participant Characteristics
At baseline there were no differences in the age, body weight or strength level (1RM)
between the two groups (see table 5).
Characteristics Placebo carbohydrate
n = 8
Whey protein isolate n = 9 Age (yrs) 22.0 + 3.6 24.2 + 5.1 Weight (kg) 77.4 + 14.1 81.5 + 7.6 Leg Press 1RM (kgs) 274 + 112 283 + 87 Leg Extension 1RM (kgs) 88 + 26 84 + 25 Leg Flexion 1RM (kgs) 40 + 8 46 + 22
Table 5. Participants’ baseline characteristics. Values are means ± SD of all seventeen males.
5.2.2 Dietary Analysis
Based on supplement dosage of 1.5g/kg.bw/day, there was no difference in the amount
of supplement ingested between the placebo carbohydrate and whey protein-
supplemented group during the 14-day recovery period (see table 5.1). One-week
dietary analysis (excluding supplementation) revealed no differences in energy, protein,
Variable Placebo Carbohydrate n = 8 Whey Protein n = 9 Supplement consumption (g/kg/day) 115.92 + 21.2 122.21 + 11.4 Energy Intake (kcal/kg/day) 30.14 + 7.3 29.43 + 5.1
Protein Intake (g/kg/day) 0.82 + 0.09 0.85 + 0.06
Fat Intake (g/kg/day) 0.94 + 0.18 0.97 + 0.18
Carbohydrate Intake
(g/kg/day) 4.58 + 1.45 4.32 + 0.95
Table 5.1. Values are means ± SD of 7-day written dietary recall of all participants submitted during the final week of the recovery period. These values do not include supplementation consumed.
5.2.3 Muscle Strength and Performance Assessment 5.2.3.1 Isokinetic Knee Extension Strength
Pre-exercise absolute values for isokinetic knee extension strength were 234 + 18 Nm
and 238 + 9 Nm for placebo and whey isolate group, respectively. No differences were
detected.
Effect of the resistance exercise: Reductions in strength (expressed as a percentage of
pre-exercise strength) persisted for 7 days and were approximately 16% lower at 24
hours post-exercise (P<0.01), 20% lower at 48 hours (P<0.01), 18% lower at 72 hours
(P<0.01), 11% lower at 96 hours (P<0.05) and 7% lower at day 7. Reductions in
strength were also observed in the whey protein-supplemented group, albeit smaller %