A prior bout of contractions speeds VO2 and blood flow on-kinetics and reduces the VO2 slow-component amplitude in canine skeletal muscle contracting in situ.
It was the purpose of this study to examine the effect of a priming contractile bout on oxygen uptake (VO2) on-kinetics in highly oxidative skeletal muscle. Canine gastrocnemii (n=12) were stimulated via their sciatic nerves (8 V, 0.2-ms duration, 50 Hz, 200-ms train) at a rate of 2 contractions/3 s (approximately 70% peak VO2) for two 2-min bouts, separated by 2 min of recovery. Blood flow was recorded with an ultrasonic flowmeter, and muscle oxygenation monitored via near-infrared spectroscopy. Compared with the first bout (bout 2 vs. bout 1), the VO2 primary time constant (mean+/-SD, 9.4+/-2.3 vs. 12.0+/-3.9 s) and slow-component amplitude (5.9+/-6.3 vs. 12.1+/-9.0 ml O2.kg wet wt(-1).min(-1)) were significantly reduced (P<0.05) during the second bout. Blood flow on-kinetics were significantly speeded during the second bout (time constant=7.7+/-2.6 vs. 14.8+/-5.8 s), and O2 extraction was greater at the onset of contractions (0.050+/-0.030 vs. 0.020+/-0.010 ml O2/ml blood). Kinetics of muscle deoxygenation were significantly slower at the onset of the second bout (7.2+/-2.2 vs. 4.4+/-1.2 s), while relative oxyhemoglobin concentration was elevated throughout the second bout. These results suggest that better matching of O2 delivery to VO2 speeds Vo(2) on-kinetics at this metabolic rate, but do not eliminate a potential role for enhanced metabolic activation. Additionally, altered motor unit recruitment at the onset of a second bout is not a prerequisite for reductions in the VO2 slow-component amplitude after a priming contractile bout in canine muscle in situ.
Department of Kinesiology, Auburn University, Auburn, AL, USA. Andres.Hernandez@ki.se
Andrés
A
Hernández
James R
JR
McDonald
Nicola
N
Lai
L Bruce
LB
Gladden
D000818:Animals; D001783:Blood Flow Velocity; D002245:Carbon Dioxide / Q000097:blood; D004285:Dogs; D004558:Electric Stimulation; D005260:Female; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D017078:Laser-Doppler Flowmetry; D008297:Male; D009119:Muscle Contraction; D018763:Muscle Fatigue; D018482:Muscle, Skeletal / Q000098:blood supply* / Q000294:innervation / Q000378:metabolism*; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption; D010108:Oxyhemoglobins / Q000378:metabolism; D011999:Recruitment, Neurophysiological; D012039:Regional Blood Flow; D012584:Sciatic Nerve / Q000502:physiology; D019265:Spectroscopy, Near-Infrared
D010108:Oxyhemoglobins; D002245:Carbon Dioxide; D010100:Oxygen