Total body skeletal muscle mass estimated by magnetic resonance imaging and creatine (methyl‐d₃) dilution in athletes

Abstract

Creatine dilution (D3‐cr) is a technique for estimating total skeletal muscle mass (SMM) with practical utility, but has not been applied in athletic populations where body composition may differ to that in the normal population. This study aimed to assess the agreement between SMM derived from both D3‐cr and that obtained from whole‐body magnetic resonance imaging (MRI) in 15 male and 5 female national level kayakers (stature: 182.0 ± 13.1 and 170.0 ± 9.0 cm; body mass: 80.6 ± 9.9 and 66.4 ± 6.0 kg; V̇O2peak: 56.5 ± 7.0 and 49.6 ± 4.4 mL kg−1 min−1, mean ± SD). SMM was determined following 60 mg of dosed D3‐cr and analysis of expelled urine collected on four subsequent days for creatine, creatinine, D3‐cr, and D3‐creatinine using liquid chromatography/mass spectroscopy. SMM was then estimated by assuming a creatine pool size of 4.3 g/kg. During the same time period, a whole‐body MRI was undertaken to derive SMM from the analysis of multiple slices taken across the body. A strong positive correlation (F = 74.32; R = 0.90; P < .0001) between the two methods was observed, but the D3‐cr SMM was found to be significantly higher (43.3 ± 6.8 kg) when compared with MRI (36.3 ± 5.8 kg, P < .0001). However, the difference between the methods was removed when a higher intramuscular creatine pool (5.1 g/kg) was assumed. These data show that D3‐cr has potential utility in athletes, as referenced against MRI, but show that assumptions regarding creatine pool size need to be carefully considered.

Combined in vivo muscle mass, muscle protein synthesis and muscle protein breakdown measurement: a ‘Combined Oral Stable Isotope Assessment of Muscle (COSIAM)’ approach

“…It is important to ensure that the constant used accurately reflects intramuscular creatine in different populations, particularly where the muscle creatine pool size may vary e.g. vegetarians [40], athletes, especially following acute or endurance exercise [41] or when creatine is being supplemented in the diet [42]. When considering the impact of dietary intake, although a large amount of creatine can be found in meat, average ingestion is ~ 1 g/day [43] in an omnivorous diet.…”

D3‐creatine dilution for skeletal muscle mass measurement: historical development and current status

“…evaluated the D 3 ‐creatine method in a sample of British national‐level male and female kayakers. 53 The observed mean creatine concentration was 5.4 and 5.3 g per kg MRI‐measured total body skeletal muscle mass, respectively. High activity levels may lead to myofibre hypertrophy, a shift in muscle fibre type, stimulate creatine uptake via increased blood flow, or promote muscle membrane creatine translocation.…”

“…Pectoral, abdominal, leg, and psoas muscles are reported to have creatine concentrations of 4.62, 3.96, 3.91, and 3.89 g/kg, respectively. 53 Some muscles, such as the intercostals, sternocleidomastoids, tongue, and diaphragm have low creatine concentrations primarily because they are rich in connective tissue that ‘dilutes’ the myofibre mass. 36 That is why some investigators express creatine per unit non‐collagen nitrogen, a surrogate measure of contractile protein and myofibrillar mass.…”

“… Association between measured mean creatine pool size and MRI‐measured total body skeletal muscle mass as reported for groups in recent publications. 7 , 33 , 53 , 64 Hypothetical slopes (creatine concentration in skeletal muscle; creatine pool size/skeletal muscle mass) are shown in the figure overlaid on actual data points. This plot shows how, in the evaluated samples, whole‐body creatine concentration of skeletal muscle varies from a low of about 3.8 to a high of 5.4 g/kg.…”

“… 33 CHF, congestive heart failure; COPD, chronic obstructive pulmonary disease. (A) Male athletes 53 ; (B) male athletes 64 ; (C) female athletes 53 ; (D) young males 7 ; (E) old males 7 ; (F) young females 7 ; (G) old females 7 ; (H) old females 33 ; (I) old males 33 ; (J) old males with CHF 33 ; (K) old males with COPD. 33 …”