Figure1: Schematic diagram showing the mechanism leading to muscle contraction. Contraction occurs when skeletal muscle fibres are activated by motor neurones. An impulse arrives by motor neurone and is transmitted via neuromuscular junction to the skeletal muscle fibre, before travelling along transverse tubules to the sarcoplasmic reticulum, which releases calcium ions into resting muscle cells (1). Resistance training can increase this neuromuscular capacity. The release of calcium ions triggers the interaction of actin and myosin filaments (2) by binding to troponin and causing a conformational change which causes tropomysosin being physically moved aside to uncover cross-bridge binding sites on the actin filaments (3), which myosin binds to pull the actin towards the centre of the sarcomere (power stroke) (4), which is powered by ATP hydrolysis. Creatine can increase the efficiency of this system by shuttling the phosphogens between the mitochondria and cytosol. Creatine kinase catalyses PCr and ADP formation in the mitochondrial matrix, allowing PCr to migrate to sites of ATP consumption, for example, in vigorous exercise, where local CK enzymes regenerate ATP (5) for increased muscular contraction. Resistance training is thought to also increase the efficiency of this system. (Adapted from [52])
Figure2: Creatine kinase catalyses the reversible reaction between creatine (Cr) and ATP to form the energy store, phosphocreatine (PCr). PCr is produced when ATP levels are high during low rates of muscular activity. PCr is then utilised when the more limited intramuscular supply of ATP is depleted during anaerobic exercise; the phosphate is transferred from PCr to ADP, to replenish ATP, a key cellular energy carrying molecule. Intramuscular supplies of PCr and ATP are limited and the combined total is estimated to sustain high-intensity exercise for approximately 10 seconds [4]
Type of muscular strength Assessment xercise Protocol
Upper-body strength    
Dynamic Bench press (kg)
Chest press (kg)		 1-reptition maximum (1-RM) = maximum amount of weight subject is able to lift in a single repetition
Isometric Arm flexion (Nm) Maximum force generated by voluntary contraction of elbow flexors as measured by strain gauge
Lower-body strength    
Dynamic Leg press (kg) 1-reptition maximum (1-RM) = maximum amount of weight subject is able to press in a single repetition
Isometric Knee extension and flexion Nm) Ankle dorsiflexion (Nm) Maximum voluntary contraction of knee and ankle flexors/extensors as measured by strain gauge
Muscular endurance    
  Repetitions of any of the above exercises at a specified load Maximum number of 1-RM a subject can repeat for the bench/leg/chest press
Functional performance    
  Tandem gait Ability to walk in a straight line, touching heel to toe with every step
  Timed sit to stand Number of completed sit-stand repetitions within 30s
  Stair climb (s) Time taken and ability to climb a pre-determined flight of stairs without assistance
  Chair rise and walk (s) Time taken to stand and walk a pre-determined distance
Table1: Summary of the main assessment protocols used to analyse muscular strength, endurance and general functional performance. Numerous assessment protocols were used for measuring strength, endurance and power. Commonly used methodologies are described below
Author Amount of Cr
supplemented per day		 No of
days		 Additional
supplements		 Bench
press
(kg)		 Leg
Press
(kg)		 Leg
extension
(kg)		 Isometric
strength		 Muscular endurance (reps
of 1-RM)		 Body
mass
(kg)		 Body composition
Bermon et al. 1998 [37] LP: 20g/day (5 days)
MP: 3g/day (47 days)		 52 - NS NS NS - NS NS Lower LMV= NS
Chrusch et al. 2001 [23] LP = 0.3g.kg-1 body mass (5 days).
MP = 0.07g.kg-1body mass (79 days) Average Cr/day:
LP 26.4g/day, MP 6.16g/day.		 84 - NS SD (20kg) SD (3.3kg)   SD Leg press
(+ 15 reps);
SD Leg extension
(+ 7 reps);
NS Bench press		 SD (+ 3.0kg) LTM = SD (+ 3.33 kg )
Brose et al. 2003 [36] 5g/day 98 - NS NS NS SD Knee Extension
(+23.7%);
SD Ankle dorsiflexion
(+ 15.6 %
males only)		 - SD (+ 1.0kg) LTM = SD (+1.3kg)
Candow et al. 2008 [31] 0.1g.kg-1 on training days
only. Average Cr/day: 8.6g
(training days only).		 70 0.3 g
Pr.kg-1		 Cr =
NS
Cr+Pr
= SD
(+10kg)		 - - - - Cr = SD
(+ 1.0 kg)
CrPr =
SD (+ 1.0
kg)		 LTM:
Cr = SD
(+ 1.5 kg);
CrPr = SD
(+ 2.6 kg );
Muscle
thickness
Cr = SD (+
4.9 % )
Bemben et al. 2010 [27] LP = 7g on training days
only (14 days). MP = 5g
on training days only (98days).		 112 35g Pr NS   Cr = NS
Cr+Pr =		 - - - LTM:
Cr = NS
CrPr = NS
Tarnopolsky et al. 2007[30] LP + MP = 5g/day 168 6g CLA NS   NS - NS Leg press;
SD Leg extension (+ 7 reps
females only);
SD Chest press (+ 4/5 reps
females/males);
SD Arm flexion (+ 10/5
reps females/males)		 NS LTM = SD
(+1.2 -1.3kg)
Chilibeck et al. 2005 [23] LP = 0.3g.kg-1 body
mass (5 days).
MP = 0.07 g.kg-1 body
mass (79 days).
Average Cr/day: LP
26.4g/day, MP: 6.16g/day.		 84 - -   - - - - BMD = NS
BMC Arm
= SD (+ 3.2
% )
Gualano et al, 2014 [34] LP = 20g/day
et MP = 5g/day		 168 - SD (+10%) SD (+19.9%) - - - --- Appendicular
LM = SD
(+1.31%)
Table 2: Summary table of key studies investigating the effect of creatine supplementation on muscular strength and power, and body composition, in elderly individuals who undertake resistance training. Cr = Creatine. LP = Loading phase. MP = maintenance phase. CLA = Conjugated linoleic acid. CrPr = Creatine and Protein. Pr = Protein. SD = significant difference. NS = no significant difference. — = Not measured. LMV = limb muscular
volume. LTM = lean tissue mass..BMC = Bone mineral content. BMD = Bone mineral density. The values (e.g. + 3.3kg/%) are the improvements made after creatine supplementation and resistance training in comparison to placebo, and were considered to be significant at p = 0.05