Noninvasive measures of blood volume and oxygen saturation of human Achilles tendon by red laser lights.

AIM: Spectroscopic measurement using near-infrared spectroscopy and red laser lights was performed to investigate the blood volume (total haemoglobin; THb) and oxygen saturation (oxygenated haemoglobin saturation; StO2) of the human Achilles tendon during single and repetitive isometric contractions.

METHODS: Twelve men performed isometric plantar flexion exercises at intensities of 10% (3 min), 30% (2 min), 50% (1 min) and 70% (30 s) of the maximum voluntary contraction (MVC). In addition, they performed 50 repetitions at 70% of the MVC with 5-s contractions and a 5-s gap between repetitions for 10 min. The probes were positioned on the Achilles tendon and medial gastrocnemius muscle.

RESULTS: THb and StO2 of the Achilles tendon decreased during 'single' contraction at all force levels. On the other hand, after the end of the repetitive exercises, THb and StO2 of the Achilles tendon increased gradually, and remained at this level until the end of the recovery period.

CONCLUSION: The blood volume and oxygen saturation within the human Achilles tendon increased after the 'repetitive' muscle contractions, while they decreased after the 'single' contraction. Furthermore, the increases in blood volume and oxygen saturation within the tendon after repetitive contractions may be related to tendon repair after exercises involving mechanical loading of the tendon.