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The bone vascular system is important; yet, evaluation of bone hemodynamics is difficult and expensive. This study evaluated the utility and reliability of near-infrared spectroscopy (NIRS), a portable and relatively inexpensive device, in measuring tibial hemodynamics and metabolic rate. Eleven participants were tested twice using post-occlusive reactive hyperemia technique with the NIRS probes placed on the tibia and the medial gastrocnemius (MG) muscle. Measurements were made at rest and after two levels of plantarflexion exercise. The difference between oxygenated and deoxygenated hemoglobin signal (HbDiff) could be reliably measured with small coefficients of variation (CV; range 5.7 – 9.8%) and high intraclass correlation coefficients (ICC; range 0.73 – 0.91). Deoxygenated hemoglobin rate of change, a potential marker for bone metabolism, also showed good reliability (CV range 7.5 – 9.8%, ICC range 0.90 – 0.93). The tibia was characterized with a much slower metabolic rate compared to MG (p < 0.001). While exercise significantly increased MG metabolic rate in a dose-dependent manner (all p < 0.05), no changes were observed for the tibia after exercise compared to rest (all p > 0.05). NIRS is a suitable tool for monitoring hemodynamics and metabolism in the tibia. However, the local muscle exercise protocol utilized in the current study did not influence bone hemodynamics or metabolic rate. Novelty bullets • NIRS can be used to monitor tibial hemodynamics and metabolism with good reliability. • Short-duration local muscle exercise increased metabolic rate in muscle but not in bone. • High level of loading and exercise volume may be needed to elicit measurable metabolic changes in bone.

Objective: To assess the reliability and reproducibility of using a four arterial occlusions protocol and near-infrared spectroscopy (NIRS) to measure resting and post-exercise muscle oxidative metabolism (mVO2). Approach: mVO2 was measured on the forearm muscles on two different days (day1 and day2) within one week in 11 healthy young adults (24.2 ± 2.7 years; 5 males). mVO2 was measured using NIRS during four repeated arterial occlusions at rest, and 5 min after exercise consisting of 90 s of rapid concentric contractions (5 minEPOC). Main results: Resting mVO2 with four measurements was 17.88 ± 3.04% min−1 on day 1 and 19.42 ± 3.03% min−1 on day 2 (p = 0.171) with a coefficient of variation (CV) of 10.1%. When using only the first measurement, the CV increased to 18.5% (p = 0.039). 5minEPOC was 212.4 ± 142.5% and 177.1 ± 125.8% higher than resting and was not different between days one and two (53.83 ± 21.17% min−1 and 52.22 ± 22.10% min−1, respectively, p= 0.199). The CV and intraclass correlation (ICC) for 5minEPOC between days one and two were, 6.5% and 0.98, respectively. Using only the first value for 5minEPOC resulted in slightly higher CV but similar ICC (7.6% and 0.98, respectively; both p > 0.05). Significance: Our results suggest that within a single testing session, one arterial occlusion can provide reproducible measurements for both resting and post-exercise mVO2 similar to that of a four arterial occlusions protocol. While a four arterial occlusion protocol provides similar reliability for post-exercise mVO2 with one arterial occlusion, it reduces the day-to-day variance for resting mVO2 and therefore should be employed for longitudinal studies.

Cerebral palsy (CP) is a movement disorder associated with small and weak muscles. Methods that accurately assess muscle mass in children with CP are scarce. The purpose of this study was to determine whether dual-energy X-ray absorptiometry (DXA) accurately estimates midleg muscle mass in ambulatory children with spastic CP. Ambulatory children with spastic CP and typically developing children 5-11 y were studied (n = 15/ group). Fat-free soft tissue mass (FFST) and fat mass at the middle third of the tibia (i.e., midleg) were estimated using DXA. Muscle mass (muscle MRI ) and muscle mass corrected for intramuscular fat (muscle MRIfc ) in the midleg were estimated using magnetic resonance imaging (MRI). Statistical models were created to predict muscle MRI and muscle MRIfc using DXA. Children with CP compared to typically developing children had lower FFST (38%), muscle MRI (40%) and muscle MRIfc (47%) (all p < 0.05) and a lower ratio of muscle MRIfc to FFST (17%, p < 0.05). DXA-based models developed using data from typically developing children overestimated muscle MRI (13%) and muscle MRIfc (22%) (both p < 0.05) in children with CP. DXA-based models developed using data from children with CP explained 91% of the variance in muscle MRI and 90% of the variance in muscle MRIfc in children with CP (both p < 0.05). Moreover, the estimates were not different from muscle MRI and muscle MRIfc (both p > 0.99). We conclude that DXA-based statistical models accurately estimate midleg muscle mass in children with CP when the models are composed using data from children with CP rather than typically developing children.

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