Creatine supplementation (year 2) Flashcards
Contamination of supplements?
An international study performed in 2001 and 2002 on 634nutritional supplements that were purchased in 13different countries showed that about 15%of the nonhormonal nutritional supplements were contaminated with anabolic-androgenic steroids
Creatine
Cr synthesized from arginine, glycine and methionine Enzymes involved synthesis of Cr located in liver, pancreas and kidney
Most of Cr pool in skeletal muscle (~95%), ~60% in a phosphorylated form (PCr)
Replenishment of Cr at similar rate by dietary intake and endogenous Synthesis
In average 70kg adult, total Cr pool in body amounts to ~120-140g
Continuous degradation of Cr to Creatine, which excreted in urine at a rate of ~2g/d
Key studies?
- Harris et al. (1992)–Cr supplementation ↑muscle [TCr] and [PCr]
- Greenhaff et al. (1993)–Cr supplementation ↑performance
- Greenhaff et al. (1994)–Cr supplementation lead to an ↑in PCr resynthesis following intense exercise
- Casey et al. (1996) & Kilduff et al. (2002)–Magnitude of ↑in performance directly related to ↑in [TCr] following supplementation
creatine supplementation protocols?
- Loading Protocol–Ingest 15-25 g/d for 5-7 days (0.3 g/kg/d)
- Loading/Maintenance Protocol–Ingest 0.3 g/kg/d (15-25 g/d) for 5-7 days–Ingest 3-5 g/d to maintain
- Low Dose Protocol–Ingest 3-5 g/d during training
Cr washout from the muscle?
4 wks
reported muscle TCr & PCr returned to baseline after 4-wks cessation
Adequate wash-out 4-6 wks
Effects of creatine on isometric bench-press performance in resistance-trained humans?
- Large intra-individual response to Cr supplementation–Responders vs. Non-responders
- Cr increased total force compared to placebo in responders
- Cr increased body mass and FFM
- Positive Correlation between uptake and performance benefit
Creatine and Body mass?
•Cr supplementation (20-25 g/d for 4-7-d and 2 to 25 g/d thereafter) has been reported to increase: –Total body mass –Fat-free mass –TBW –ICW
•Gains are typically 0.8 to 3.0 kg greater than controls depending on the length and amount of supplementation
Creatine and Body mass: mechanisms?
•Mechanisms?
–Water Retention
–Protein synthesis
Short-Term Cr supplementation: no effect?
- Eight active, untrained men performed a 20-s maximal sprint on an air-braked cycle ergometer after 5 days of CrS
- The trials were separated by 4 wk, and a double-blind crossover design was used
- Following Cr supplementation subjects increased their muscle Cr content by 11.7 ±2.4 mmol/kg dry mass (range 2.9–19.9)
Short-Term Cr Supplementation: No effect, further research?
- McKenna et al (J Appl Physiol. 87:2244-52, 1999)reported that creatine (30 g/d x 5-d) did not affect 5x10-s sprints with rest intervals of 180, 50, 20, and 20-s in 14 untrained subjects.
- Following Cr supplementation subjects increased their muscle Cr content by 22.9 ±4.2 mmol/kg dry mass
- Finn et al (Eur J Appl Physiol. 84:238-43, 2001)reported that creatine (20 g/d x 5-d) increased TCr in 16 triathletes. No effects were seen in PCr or cycling sprint performance (4 x 20-s with 20-s rest recovery).
- Following Cr supplementation subjects increased their muscle Cr content by 16 mmol/kg dry mass
critique of the negative studies?
•Single bout of exercise (Snow et al., 1998)
•Only moderate elevation in [TCr] therefore no ergogenic effect expected
–11.7 ±2.4 mmol/kg dry mass (range 2.9–19.9) (Snow et al., 1998)
–22.9 ±4.2 mmol/kg dry mass (McKenna et al., 1999)
–16 mmol/kg dry mass (Finn et al., 2001)
- Recovery between bouts not sufficient (McKenna et al., 1999; Finn et al., 2001)
- Small sample size (n=8, Snow et al., 1998; n=7, McKenna et al., 1999)
Short-term Cr Supplementation: summary?
- Nearly all studies indicate that Cr loading increases TCr and PCr.
- Responders vs Non-responders •About 80% of short-term studies report some ergogenic benefit particularly during high-intensity, repetitive exercise. –↑Exercise in the Heat (mechanism) –↑Mild Sleep Deprivation (mechanism)
- Benefits have been reported in untrained, trained, diseased adults, and elderly populations.
•Studies reporting no ergogenic benefit typically have
–Low statistical power
–Subjects have relatively low muscle Cr uptake
–Study design not optimal for effect
Long-term creatine supplementation?
•Voleketal(MedSciSportsExerc.31:1147-56,1999)reportedthat12-wk of creatine supplementation (25g/dx7-d&5g/dx77-d)during periodized resistance training increased muscle TCr and PCr, FFM, BP & squat 1RM, and lifting volume (wks5-8) with no side effects observed 19 resistance trained athletes.
Long-term Creatine supplementation, part 2?
reported that creatine supplementation (20 g/d x 4-d & 5 g/d x 65-d) during 10-wks of training in women increased TCr & PCr, maximal strength of the muscle groups trained (20-25%), maximal intermittent exercise capacity of the arm flexors (10-25%), and FFM (60%)more than subjects ingesting a placebo.
•Creatine supplementation during 10-wks of detraining maintained training adaptations.
Medical concerns described in popular and scientific literature?
•Proposed Medical Concerns:
Suppressed Cr Synthesis
Renal Stress
Muscle/Liver Damage
Altered Fluid/Electrolyte Status
Hypertension “Unknown” Long-term Side Effects
