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The Creatine Craze

What is creatine?

Creatine (Cr) is a naturally occurring compound composed of three amino acids; arginine, glycine, and methionine (Casey & Greenhaff, 2000). The liver, kidneys and pancreas can synthesise creatine and it can also be accumulated by ingesting meat. Around 95% of the total Cr pool is stored within skeletal muscle, with 60% as phosphocreatine (PCr) (Casey et al., 1996). As muscle tissue cannot synthesize Cr, it is reliant upon specific membrane sodium dependent transporters for Cr uptake (Longo et al., 2011). A meta-analysis of 48 studies reported that progressive resistance training (PRT) and supplementation with either Cr or Hydroxy Methylbutyric acid (HMB) gave significant increases in lean mass and strength, whereas supplementation with other products did not (Nissen & Sharp, 2003).

How does creatine increase strength and function?

The dephosphorylation of adenosine triphosphate (ATP) releases energy that can be utilised by muscles for contraction and relaxation.

ATP ↔ adenosine diphosphate (ADP) + phosphate (Pi) + ENERGY

(catalysed by the enzyme ATPase)

The concentration of ATP in skeletal muscle is ~ 24 mmol· kg/dw (Harris et al., 1974) which can be exhausted within 1 – 2 seconds by maximal exercise (Burton et al., 2004). Anaerobic and/or or aerobic pathways can replenish depleted stores of ATP.

Dephosphorylation of PCr releases stored energy and a phosphate molecule that can be used to resynthesize ATP. With PCr stores in the muscle being 3 – 4 times higher than ATP stores (Bogdanis et al., 2007), it is a pathway that can offer relatively quick replenishment of ATP levels.

ADP + PCr ↔ ADP + Cr + Pi + ENERGY ↔ ATP + Cr

(catalysed by the enzyme creatine kinase)

Hence, the increase of PCr stores, by the ingestion of Cr supplements, may delay PCr depletion allowing for more resynthesise of ATP and by extension allowing more muscle contractions and relaxations.

Loading and maintenance schemes

Loading schemes are used to increase the total muscle Cr (TCr) within the body above that of normal within a short time period. An effective (and the most commonly used) loading scheme involves Cr supplementation of 20 g/day (in four 5 g doses) for 5 days (Harris et al., 1992). Following the loading phase, maintenance schemes such as 2–5 g/day of Cr (Hultman et al., 1996) are used to sustain the increased TCr.

Responsiveness to creatine

Between 20 – 30 % of individuals do not increase TCr following 5 days of Cr supplementation at 20 g per day and can be classed as ‘non-responders’(Greenhaff et al., 1995). Individuals that do increase TCr following the loading phase, known as ‘responders’, typically have a biological profile including: low initial levels of TCr, higher percentage of type II fibres and a higher preload muscle fibre cross-sectional area (Syrotuik et al., 2004).

Safety of creatine

It is widely believed that Cr supplementation may have associated health risks yet to the authors knowledge this is not supported by research. Participants receiving high doses of Cr supplementation (10 g/day) (Earnest et al., 1996; Gualano et al., 2008) or involved with long term studies (< 5 yrs) (Poortmans & Francaux, 1999) reported no adverse side effects. More importantly, it appears Cr supplementation has no negative effect on established anti-inflammatory and immunosuppressive medical treatments for patients suffering chronic idiopathic inflammatory myopathies (Chung et al., 2007). Consequently, it appears that Cr supplementation, using the previously suggested loading and maintenance schemes, has no associated health risks.

Effects of creatine on physical function

Creatine supplementation has been shown to improve performance in both single and repeated bouts of high-intensity exercise (Branch, 2003), and combining Cr supplementation with PRT can give greater increases in strength then PRT alone (Larson-Meyer et al., 2000). The combined improvements in strength and the capability to repeat high-intensity exercise increase work capacity. An increase in work capacity can lead to greater gains in muscle mass from PRT (Olsen et al., 2006) and improved physical function capacity (Baumgartner et al., 2004; Marcora et al., 2005a; Giles et al., 2008a).

The effects of creatine on muscle mass

An increase in skeletal muscle cell Cr and PCr concentrations initially causes osmotic pressure to decrease making the cell hypotonic. Subsequently extracellular water (ECW) will be drawn into the cell to make it isotonic (Lang et al., 1998). The body will begin to retain water a few days after supplementation to restore the ECW that has shifted to increase intracellular water (ICW). This can increase body mass (BM) by 1 – 2 kg (Powers et al., 2003). The increase of intracellular Cr and ICW increases mechanical strain on the muscle cell, which in turn may stimulate protein synthesis and inhibit proteolysis (Ingwall et al., 1974). Although this theory is widely accepted, some research has produced results that refute this mechanistic pathway (Francaux & Poortmans, 2006).

Creatine supplementation may also increase muscle mass by increasing muscle Insulin-like Growth Factor-1 (IGF-1) concentrations (Deldicque et al., 2005; Burke et al., 2008), a hormone that is both anabolic and anti-catabolic and a key mediator in the maintenance and hypertrophy of adult human muscle (Adams (2002) J Appl Physiol 93: 1159-1167). Additionally, when Cr supplementation is combined with PRT it may reduce serum myostatin concentrations (Saremi et al., 2010). Myostatin is a catabolic hormone that has also been linked to joint destruction in and age-related muscle loss in humans (Dankbar et al., 2011; Leger et al., 2008). The increase in muscle IGF-1 concentrations combined with the decrease in serum myostatin concentrations may cause a positive net protein balance and by extension, contribute to the increase in muscle mass observed following Cr supplementation.

Summary

Supplementing your regular diet with Cr will be beneficial if you are looking to improve physical function and/or muscle mass. By extension, if you are looking to reduce body fat % I would also recommend creatine supplementation (I will discuss in a later blog how creatine will improve body composition). As always if you have any questions about any Cr or want any further details on any of the references please get in contact

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