Please see Bibliography of References for a list of abstracts, manuscripts and posters.
Crenshaw AG, Bronee L, Krag IR, Jensen BR. ACSM Annual Meeting; May 30-June 2, 2007; New Orleans, LA.
Non-uniformity in oxygen saturation (StO2) for a single muscle has been reported by use of near infrared spectroscopy (NIRS). In general, StO2 changes (i.e. drop) are reportedly greater for distal muscle sites as compared to proximal. While most existing data entail contractions of one magnitude, a few studies have focused varying magnitudes of dynamic contractions; however, little is known of StO2 distributions during isometric contractions at different contraction levels.
Purpose: To determine StO2 kinetics for the proximal and distal regions of the vastus lateralis muscle (VL) during isometric contractions of 15% and 30% MVC for knee extension.
Methods: Nine male subjects (mean age: 28.8 yrs) performed a protocol consisting of a 2-min isometric knee extension at 15% MVC, and after a rest period 30% MVC was performed. During contractions StO2 was monitored with a 25-mm NIRS probe (Inspectra 325, Hutchinson Technology) placed on a proximal site of the right VL. After recovery the protocol was repeated and StO2 was monitored at a distal VL site. The following StO2 variables were identified and tested for differences using repeated measures ANOVA with factors location (proximal vs distal) and force (15% vs 30% MVC) incorporated: (i) slope of change at the start of contraction (slope-start); (ii) maximum change from rest (max-drop); (iii) transient increase from max-drop during contraction (up-value); (iiii) slope of recovery at the end of contraction (slope-end).
Results: Resting values (89.1 proximal, 86.4 distal) were independent of location. However, the relationship and mean values for max-drop across location and force were distal 30% MVC (-73.3%StO2) >proximal 30% MVC (-57.6%StO2) >distal 15% MVC (-26.9%StO2) >proximal 15% MVC (-17.0%StO2). The rank of response for the other variables followed the same trend. For all variables, except the up-value, there was either a tendency for or significance due to location (maximum P = 0.08) and to force (maximum P = 0.04). Furthermore, for slope-start a significant interaction for location x force (P = 0.04) was detected.
Conclusion: The study provides longitudinal data for StO2 at different isometric contraction forces. Greater responses distally can be attributed to architectural differences between regions, which give way to higher intramuscular pressures.