Detection of Anaerobic Threshold using Near Infra Red Spectroscopy on Gastrocnemius Muscle in Runners

Abstract

Near infra red spectroscopy (NIRS) has been suggested as a non-invasive methodology providing measures of tissue oxygen saturation (StO2) and detecting ventilatory threshold during an incremental protocol. However, there are not any data regarding application of NIRS on gastrocnemius muscle, which is one of the dominant muscles during running. PURPOSE: This study was designed to evaluate two different methods of detecting a threshold employing NIRS on gastrocnemius muscle and correlate them to ventilatory threshold in runners. METHODS: Nine male healthy subjects [(M±S) age: 22.4±0.88 yrs, height: 176.9±7.70 cm, body mass: 73.7±9.48 kg, VO2max: 49.9±5.16 ml kg-1 min-1, vVO2max: 14.8±1.46 km h-1], performed an incremental maximum exercise test on a treadmill. Initial speed was set at 8 km h-1 with increments of 0.5 km h-1 per minute. The NIRS probe was placed on the left gastrocnemius muscle belly, parallel to the longitudinal axis of the lower leg. Running speed at the NIRS threshold was evaluated with StO2-speed plots, employing two different models: linear (NTlin) and Dmax (NTD) (Cheng et al., 1992). Criteria of assessing ventilatory threshold (VT) included the V-slope method, VE/VO2 - VE/VCO2 and PetO2 - PetCO2 plots. RESULTS: Mean ± S values for VT, NTlin and NTD were 12.17±0.97, 12.17±1.00, and 12.20±0.97 km h-1 respectively. No significant differences were found between VT and NTlin or NTD (p>0.05). VT was significantly correlated (p<0.05) to NTlin (r=0.72), and NTD (r=0.86). CONCLUSIONS: NIRS methodology applied on gastrocnemius muscle seems to provide a useful means of detecting a threshold in running. Both models employed were significantly correlated with VT, with Dmax model showing higher correlation than NTlin model. These findings, as well as the appropriateness of the NIRS methodology in prescribing exercise training in runners, need to be further investigated.