Skinfold Thickness

START has been granted ethical approval locally from the Research Ethics Board, Hamilton Health Sciences/McMaster Health Sciences (REB#: 10-640) and in India, Institutional Ethics Review Board Reference #: 114/2010). In both countries, pregnant mothers are recruited during their antenatal visits (1^st or 2^nd trimester) to their primary care practitioner or obstetrician. The study is described by the study personnel to the pregnant mothers and consent for participation is obtained. Information concerning medical and pregnancy history, health status, health behaviors, and socioeconomic status is obtained by questionnaires. Anthropometric measurements (height, weight, skinfold thickness), blood pressure, urine sample, and a fasting blood sample for glucose, insulin, micronutrients (i.e. vitamin B12, RBC folate, plasma homocysteine, methylmalonic acid MMA), lipids and a buffy coat for future DNA extraction will be collected, and processed using a standardized protocol at 24-28 weeks of gestation. Mothers who are not known to have diabetes will undergo a 75 oral glucose tolerance test between 24-28 weeks gestation. The results of an ultrasound performed between 18-24 weeks to assess for congenital anomalies and for precise determination of gestational age will be collected from each pregnant mother. At the time of delivery, details of the delivery, birth outcomes for the mother and baby will be collected, and a cord blood sample for DNA, glucose, insulin, lipids and additional aliquots for future analysis of adiponectin, and leptin will be taken from each baby. The placenta will be weighed, and where possible a biopsy of the placenta will be collected and stored in RNAlater for future analysis of RNA and methylation patterns. In addition, the infant’s anthropometry including birth weight, triceps and sub-scapular skin fold thickness, length, abdominal, head, and arm circumference will be measured by a trained research assistant.

At the in-person visit, trained research assistants measured height to the nearest 0.1 cm using a calibrated stadiometer (Shorr Productions, Olney, Maryland) and weight to the nearest 0.1 kg using a calibrated scale (Tanita model TBF-300A, Tanita Corporation of America, Inc., Arlington Heights, IL). We computed each child’s BMI using the following formula: BMI=weight/height² (kg/m²). We calculated age-sex-adjusted BMI z-score and BMI percentile using the 2000 Centers for Disease Control and Prevention reference data [20 ].
We measured subscapular (SS) and triceps (TR) skinfold thicknesses to the nearest 0.1 mm using Holtain calipers (Holtain Ltd, Crosswell, Wales) and calculated the sum (SS + TR) and ratio (SS:TR) of the two thicknesses. The correlations of other measures of adiposity with subscapular or triceps thickness individually were very similar to the correlations with sum of the two, so we chose to show results for only sum of skinfolds. We measured hip and waist circumferences to the nearest 0.1 cm using a Hoechstmass measuring tape (Hoechstmass Balzer GmbH, Sulzbach, Germany), and calculated waist-to-hip circumference ratios. We measured middle upper arm circumference using a Ross measuring tape (Ross Products Division, Abbott Laboratories Inc., Columbus, OH).
Research assistants performing the measurements followed standardized techniques [21 ] and participated in biannual in-service training to ensure measurement validity. Inter- and intra-rater measurement errors were within published reference ranges for all of the measurements [22 ]. Experienced field supervisors provided ongoing quality control by observing and correcting measurement technique every 3 months.
We measured bipolar bioelectrical impedance using a Tanita scale model TBF-300A (Tanita Corporation of America, Inc., Arlington Heights, IL) foot-to-foot body composition analyzer. We calculated fat mass and fat-free mass indices for DXA and bioelectrical impedance measurements using the following formula: (mass in kg)/(height in meters)².
Trained research assistants performed whole body DXA scans on the children (n=875) using a Hologic model Discovery A (Hologic, Bedford, MA) that they checked for quality control daily by scanning a standard synthetic spine to check for machine drift. We used Hologic software QDR version 12.6 for scan analysis. A single trained investigator (CEB) checked all scans for positioning, movement, and artifacts, and defined body regions for analysis. Intrarater reliability on duplicate measurements was high (r=0.99).

Fourteen trained, and recreationally trained cyclists (7 females & 7 males, 74.1 ± 10.5 kg, 32.1 ± 7.6 years of age, 170.0 ± 11.0 cm, 11.3 ± 5.4 mm VL skinfold thickness, and 55.0 ± 9.1 ml·kg·min⁻¹ maximum oxygen uptake) volunteered and provided written informed consent to participate in the study (19 (link)). To obtain sufficient power of β = 0.8 with α = 0.05, an a priori sample size calculation was made in G*Power software (version 3.1.9.7, Kiel, Germany) using previously reported data from other groups that compared SmO₂ values within and between sessions during ramp incremental tests and severe intensity efforts (16 (link), 20 (link)–23 (link)). This study was approved by the research ethics committee of The University of British Columbia and was conducted in accordance with principles established in the Declaration of Helsinki, except for registration in a database.

Two wearable NIRS sensors (Moxy Monitor, Fortiori Design LLC., Hutchinson, USA) were used during the test. The Moxy monitor employs four wavelengths of near-infrared light (680, 720, 760, and 800 nm), with source detector separation of 12.5 and 25 mm (10 (link)). The sensors were placed on the right and left VL, and the right side was used for analysis and the left was used in case of right sensor failure. In all but one participant, the right sensor was used. The anatomical location on the VL was 1/3 the distance from the proximal pole of the patella to the greater trochanter. Left and right sensors were held in place by the participants' elastic cycling shorts, and both sensors were covered using a light shield supplied by the manufacturer to minimize ultraviolet light interference.
During instrumentation, skinfold thickness was measured and recorded from the right VL with a Harpenden skinfold caliper (Creative Health, Dallas, USA). According to the manufacturer, the Moxy sensor does not require calibration (10 (link), 11 (link)). Prior to each trial, the sensor was charged, and both the emitter and receiving optodes were cleaned.

Anthropometric data were assessed, including standing body height, leg length, body mass (BM), and body fat percentage (% fat). All measurements were taken by the same person three times using techniques established by the international biological program [31 ]. Circumferences and skin-fold thickness at different levels of the thigh and the calf, the length of the lower, and the femoral condyles breadth are measured to estimate the muscle volume of the lower limbs [29 (link)]. Muscle volumes were estimated in accordance with Eq. 1 $$\text{Muscle}\text{volume}=\text{total}\text{limb}\text{volume}-\left(\text{fat}\text{volume}+\text{bone}\text{volume}\right)$$
The total limb volume was estimated as the volume of a cylinder, based on its length (L), corresponding to the distance from the trochanter major to the lateral malleolus for the lower limb, and the mean of five limb circumferences lower limbs (for the maximal thigh, mid-thigh, just below the patella, maximal calf and just above the ankle) in accordance with Eq. 2 $$\text{Total}\text{limb}\text{volume}=\left(\sum \text{C2}\right)·\text{L}/62.8$$ where ∑C2 is the sum of the squares of the five circumferences of the corresponding limb. Skin folds were assessed using a standard Harpenden calliper (Baty International, Burgess Hill, Sussex, UK). The fat volume was calculated using Eq. 3 $$\left(\sum \text{C}/5\right)·\left(\sum \text{S}/\text{2n}\right)\text{L}$$ where ∑S is the sum of four skinfolds for the lower limb (front of mid-thigh, back of mid-thigh, back of calf and outside of calf) and ''n'' represents the number of skin folds measured.
Bone volume was calculated as $$\pi ·\left(\text{F}·\text{D}\right)2·\text{L}$$ where D is the femoral intercondylar diameter, F is a geometric factor (0.235 for the lower limb), and L is the limb length as measured above.
Bone volume was calculated as π ∙ (F ∙ D) 2∙ L, where D is the femoral intercondylar diameter, F is a geometric factor (0.235 for the lower limb), and L is the limb length as measured above.