Muscle Oxygenation Measured by Near-infrared Spectroscopy with Different Loads and Velocities of Resistance Exercise

Abstract

Near-infrared spectroscopy (NIRS) is a non-invasive optical technique widely used to monitor muscle oxygenation (Mox) during various tasks, particularly during aerobic or isometric exercise, with very few studies related to resistance exercise (RE). Load and velocity of movement are two variables that affect performance in RE, but the physiological reasons for this are not fully understood. NIRS could be a useful technique to investigate fatigue in different RE protocols. PURPOSE: To compare maximum number of repetitions to volitional fatigue (REPS) and Mox variables measured by NIRS (MicroRunman, NIM Inc., PA) during knee extensions with light (L: 60% 1RM) and heavy (H: 80% 1RM) loads, at either slow (S: 25°.s−1) or fast (F: 80°.s−1) movement velocities. METHODS: Informed consent was obtained from 9 healthy volunteers (35.8 ± 10.8 yr; 74.2 ± 16.7 kg; 171.0 ± 10.0 cm). After determining 1RM load for knee extension of the dominant leg, subjects reported to the laboratory on 4 different occasions, separated by at least 48 h, when they randomly performed 1 set of REPS with different combinations of loads and velocities: LS, LF, HS and HF. A repetition was considered valid if range of motion was at least 60°. The NIRS probe was positioned over the vastus lateralis (∼16 cm above knee joint) and Mox was continuously monitored during 2 min rest, REPS and 3 min recovery. In addition to REPS, variables considered for analysis after adjustment for baseline were: minimum during REPS and/or recovery (MIN), and range from MIN to maximum during recovery (RANGE). RESULTS: Paired t-tests showed significant (p <.05) differences in REPS (LS = 8.8 ± 1.3; LF = 16.3 ± 3.9; HS = 5.9 ± 0.9; HF = 9.4 ± 1.9) between speeds (LS × LF and HS × HF) and between loads (LS × HS and LF × HF). However, none of the comparisons for either MIN (OD; LS = −0.218 ± 0.111; LF = −0.177 ± 0.093; HS = −0.217 ± 0.107; HF = −0.204 ± 0.098) or RANGE (OD; LS = 0.241 ± 0.122; LF = 0.230 ± 0.114; HS = 0.266 ± 0.139; HF = 0.253 ± 0.136) were significant. Pearson correlation between REPS and Mox variables was significant only for LF MIN (r = −0,73; p = 0,026). CONCLUSIONS: Mox does not seem to be related to performance during RE to volitional fatigue, suggesting that the level of muscle oxygenation may not be a factor limiting this type of exercise. Further studies using NIRS during RE should be conducted to confirm these findings. Partly supported by CAPES/Ministry of Education, FAPERJ (E-26/170.774/2003), and Righetto Fitness Equipment, Brazil.