Hemoglobin near-infrared spectroscopy and surface EMG study in muscle ischaemia and fatiguing isometric contraction

Background. To assess how muscle ischaemia and isometric fatiguing contract ion influence oxygen content in striated muscle. Methods. We simultaneously measured changes in hemoglobin near-infrared (NI R) spectroscopy and in surface EMG before, during, and after muscle ischaem ia and ischaemia plus muscle isometric fatiguing contraction, Seventeen hea lthy male subjects (age range: 19-40 yrs) were examined in our Clinical Neu rophysiology Unit. Test I (9 subjects): hemoglobin NIR spectroscopy and sti mulated surface EMG were measured for 2 minutes at rest, for 4 minutes duri ng complete ischaemia of tibialis anterior muscle, and for twelve minutes d uring recovery. Test II (all subjects): hemoglobin NIR spectroscopy and sur face EMG were measured for 2 minutes with the subjects performing brief non -fatiguing contractions, for 4 minutes with the subject performing maximal isometric contraction in complete ischaemia, and for twelve minutes during recovery. EMG parameters measured: median density frequency (MDF); muscle f iber conduction velocity (MFCV). NIR spectroscopy parameters measured: perc entage of amplitude decrement (%AD) and nadir time (NT) during ischaemia an d ischaemic effort; half-recovery time (1/2 RT) from ischaemia effort. Results. At EMG, we observed a significant shift towards lower values of bo th MFCV and MDF during fatiguing isometric contraction, MDF recovery was fa ster then MFCV recovery. At NIR spectroscopy, the 1/2 RT slowed a fast patt ern in twelve subjects and a slow pattern in five. 4 significant relationsh ip was found between AD% and 1/2 RT values of test I and AD% and 1/2 values of test II, We found a positive relationship between NT and 1/2 RT in test II, Conclusions, Surface EMG and hemoglobin NIR spectroscopy can be applied sim ultaneously to evaluate both fatigue intensity and blood flow changes in st riated muscle.