The main aim was to examine the effects of measurement depth on tissue oxygenation, and haemoglobin kinetics in the oxidative supraspinatus/trapezius muscle and in the deltoid muscle. Seven female subjects performed dynamic arm abductions (0.5 Hz) with an external load of 1.2 kg at level of the elbows. Tissue oxygenation (StO2) expressed as %StO2 saturation, total haemoglobin (HbT) , oxyhaemoglobin (HbO2) and deoxyhaemoglobin (Hb) were measured in two different measurement depth using near infrared spectroscopy (NIRS). HbT reflects blood volume. Measurements were performed simultaneously in the supraspinatus/trapezius and in the anterior part of the deltoid muscles.

The average StO2 level at rest was in general lower in the supraspinatus/trapezius muscles (67.7(5.3) % StO2) than in the deltoid muscle (85.4(4.4) % StO2). Submaximal dynamic arm abductions resulted in decreased StO2 in both muscles. However, the initial decrease was steeper and larger for the deltoid muscle than for the supraspinatus/trapezius region. Correspondingly, the initial reoxygenation in the recovery phase was faster for the deltoid muscle than for the supraspinatus/trapezius muscle.

At rest no differences in StO2 were found with increasing measurement depth in any of the two muscles. However, during exercise StO2 decreased with increasing measurement depth in the deltoid muscle whereas StO2 was more homogeneous in the supraspinatus/trapezius muscle.

Furthermore, HbT and HbO2 were largely maintained in the supraspinatus/trapezius muscle whereas HbT and HbO2 decreased during exercise and with increasing measurement depth (HbT) in the deltoid muscle. Hb increased during exercise in both muscles.

The hemodynamic differential responses to exercise for the two regions may reflect a combined effect of differences in muscle fibre composition and a dependency of depth related changes in the intramuscular pressure during exercise. Thus, the supraspinatus/trapezius muscles seems to be more

efficiently adapted to the oxygen demand during submaximal dynamic exercise than the deltoid muscle although the intramuscular pressure during the contractions is expected to be higher in the supraspinatus muscle than in the deltoid muscle.

In conclusion, muscle hemodynamic responses to dynamic exercise are highly muscle specific and may be spatially homogeneous or inhomogeneous depending on the muscle