Relationship between muscle architectural features and oxygenation status determined by near infrared device

This study tested whether regional differences in oxygenation status could result from differences in muscle fiber architecture. Architectural properties, oxygen supply, and consumption in the medial head of the gastrocnemius muscle (GM) were determined in vivo in six men using B-mode ultrasound and functional near infrared (NIR) imaging devices. Fascicle length, fascicle angle, NIR-O₂ saturation (deoxygenated Hb or oxygenated Hb), and NIR-blood volume (sum of deoxygenated and oxygenated Hb) were obtained in the distal and proximal portions of the GM at rest and during contraction. Exercise consisted of 2 min of standing plantar flexion at 1 Hz with an additional load of 50% of each subject’s weight. Plantar flexion produced larger decreases (Δ: difference between rest and exercise values) in NIR-O₂ saturation [mean saturation (SD) of 0.14 (0.05) vs 0.07 (0.04) optical density units] and NIR-blood volume [mean saturation (SD) of –0.23 (0.08) vs −0.13 (0.04) optical density units] in the distal compared with the proximal portion (P<0.05 for all comparisons). It also produced larger changes (Δ) in fascicle length [mean length (SD) of –16.5 (4.7) vs −8.2 (4.2) mm] and fascicle angle (mean angle (SD) of 10.8 (1.4)° vs 3.9 (2.1)°] in the distal compared with the proximal portion (P<0.05 for all comparisons). There were significant correlations between ΔNIR-O₂ saturation and Δfascicle length (r=−0.84, P<0.05), and between ΔNIR-O₂ saturation and Δfascicle angle (r=−0.90, P<0.05), between ΔNIR-blood volume and Δfascicle length (r=0.91, P<0.05), between ΔNIR-blood volume and Δfascicle angle (r=−0.85, P<0.05). In conclusion, the plantar flexion exercise produced regional differences in oxygenation status consistent with regional differences in muscle architecture.