THE EFFECT OF SHORT- AND LONG-TERM AEROBIC TRAINING YEARS ON SYSTEMIC O-2 UTILIZATION, AND MUSCLE AND PREFRONTAL CORTEX TISSUE OXYGEN EXTRACTION IN YOUNG WOMEN
JOURNAL OF STRENGTH AND CONDITIONING RESEARCH
Authors: Buzza, Gavin; Lovell, Geoff P.; Askew, Christopher D.; Solomon, Colin
This study aimed to determine if systemic O-2 utilization (Vo2) and tissue oxygen extraction (deoxyhemoglobin [HHb]) in the vastus lateralis (VL), gastrocnemius (GAST), and prefrontal cortex were different during exercise between short-term trained (STT, 6-24 months) and long-term trained (LTT, >5 years) young women while controlling for current training load. Thirteen STT and 13 LTT participants completed ramp incremental (RI) and square-wave constant load (SWCL) tests on a cycle ergometer. In LTT compared with STT: (a) (V)over dotO(2) was higher during the RI (p = 0.024) and SWCL (p = 0.001) tests; (b) HHb in the VL (p = 0.044) and GAST (p = 0.027) was higher in the RI test; and (c) there were significant group X intensity interactions for Vol in the SWCL test. The additional years of aerobic training in LTT compared with STT (LTT 7.1 +/- 1.9 vs. STT 1.5 +/- 0.4 years) resulted in higher Vol and HHb in the VL and GAST. These results indicate that in young women, independent of current training load, systemic Vol and peripheral muscle 02 extraction during exercise continues to increase beyond 24 months of aerobic training.
THE ONTOGENY OF SHIVERING THERMOGENESIS IN THE RED-WINGED BLACKBIRD (AGELAIUS-PHOENICEUS)
JOURNAL OF EXPERIMENTAL BIOLOGY
Authors: OLSON, JM
The ontogeny of shivering thermogenesis was investigated in the altricial red-winged blackbird (Agelaius phoeniceus). Two indices of heat production - the rate of oxygen consumption (V-O2) of the bird and the electromyographic (EMG) activity of the pectoralis (PECT) and gastrocnemius (GAST) muscles - were measured simultaneously in adult and nestling red-winged blackbirds as they were subjected first to thermoneutral temperatures and subsequently to progressively colder ambient temperatures (T-a). The ontogenetic changes in bath indices indicated that the capability for thermogenesis in nestling red-winged blackbirds improved markedly with age. The metabolic rates of 3-day-old nestlings decreased during exposure to gradually falling ambient temperatures; at best, these nestlings were only able to maintain mass-specific V-O2 at levels similar to or slightly above the resting metabolic rate at thermoneutral temperatures (RMR) for a short time before metabolic rates decreased with further cooling. Shivering was detected only in the PECT muscles and was of a relatively low intensity (maximum of sevenfold increase in intensity over basal levels). The 5-day-old nestlings increased mass-specific V-O2 modestly (approximately 1.4-fold) above RMR and attained slightly higher maximal factorial increases in the EMG activity of the PECT (maximum of 18-fold basal levels) when exposed to the same experimental conditions. Shivering was also detected in the GAST muscles of these birds. The most striking improvements in both measures observed during the nestling period occurred between day 5 and day 8. Eight-day-old nestlings increased metabolic rates by approximately 2- to 2.5-fold over basal levels and sustained these elevated rates for longer before becoming hypothermic. Both the PECT and GAST muscles contributed significantly to shivering thermogenesis, and these older nestlings attained much higher factorial increases in the intensity of shivering (up to 72-fold) during exposure to cold temperatures. In addition, both the range and magnitude of the dominant frequencies of muscle activity in the PECT increased during postnatal development. The PECT muscles were a principal site of shivering thermogenesis in all nestling and adult red-winged blackbirds studied here. Shivering in these muscles was a 'first line defense' against cold; the threshold temperature for shivering in the PECT muscles coincided with the lower critical temperature for oxygen consumption (T-LC), and the subsequent increases in EMG activity in this muscle with further cooling correlated well with the corresponding increases in mass-specific V-O2.