Working the Right Side of the VO2Max Equation - Research Says that Hitting 100 Percent of VO2Max is Key Excerpt: "But how can max stroke volume and arteriovenous difference be optimized? Back in the day, the answer was to run tons of miles, but research paints a quite-different picture. In one study, 12 individuals employed a training intensity of close to 100 percent of VO2max over a seven-week period, while 12 other subjects worked out at a moderate, "aerobic" intensity of 60 percent of VO2max (about 75 percent of max heart rate). The latter, "aerobic" group actually trained for considerably longer periods of time - but achieved a 38-percent lower increase in VO2max after seven weeks, compared with the 100-percenters. This result prompted the researchers to conclude that training at an intensity which elicits VO2max has the strongest, positive impact on VO2max expansion. In a separate investigation carried out with experienced runners, one group ran about 100 kilometers per week at average intensities of 60 to 80 percent of VO2max, while a second group trained only 50 kilometers per week while emphasizing fast-paced intervals which ranged in distance from 60 to 1000 meters. After 14 weeks of training, the low-mileage, higher-intensity runners improved VO2max by 7 percent, while the high-mileage, "aerobic" runners failed to upgrade VO2max at all. Performance times improved by about 2.5 percent in the high-intensity group but failed to budge for the "aerobic" harriers."

Aerobic high-intensity intervals improve VO2max more than moderate training. by Hoff et al. Excerpts... "PURPOSE:: The present study compared the effects of aerobic endurance training at different intensities and with different methods matched for total work and frequency. Responses in maximal oxygen uptake (V O2max), stroke volume of the heart (SV), blood volume, lactate threshold (LT), and running economy (CR) were examined. METHODS:: Forty healthy, nonsmoking, moderately trained male subjects were randomly assigned to one of four groups:1) long slow distance (70% maximal heart rate; HRmax); 2)lactate threshold (85% HRmax); 3) 15/15 interval running (15 s of running at 90-95% HRmax followed by 15 s of active resting at 70% HRmax); and 4) 4 x 4 min of interval running (4 min of running at 90-95% HRmax followed by 3 min of active resting at 70%HRmax). All four training protocols resulted in similar total oxygen consumption and were performed 3 d.wk for 8 wk. RESULTS:: High-intensity aerobic interval training resulted in significantly increased V O2max compared with long slow distance and lactate-threshold training intensities (P < 0.01).="" the="" percentage="" increases="" for="" the="" 15/15="" and="" 4="" x="" 4="" min="" groups="" were="" 5.5="" and="" 7.2%,="" respectively,="" reflecting="" increases="" in="" v="" o2max="" from="" 60.5="" to="" 64.4="" ml.kg.min="" and="" 55.5="" to="" 60.4="" ml.kg.min.="" sv="" increased="" significantly="" by="" approximately="" 10%="" after="" interval="" training="" (p="" />< 0.05). conclusions:: high-aerobic intensity endurance interval training is significantly more effective than performing the same total work at either lactate threshold or at 70% hrmax, in improving v o2max. the changes in v o2max correspond with changes in sv, indicating a close link between the two." 0.05).="" conclusions::="" high-aerobic="" intensity="" endurance="" interval="" training="" is="" significantly="" more="" effective="" than="" performing="" the="" same="" total="" work="" at="" either="" lactate="" threshold="" or="" at="" 70%="" hrmax,="" in="" improving="" v="" o2max.="" the="" changes="" in="" v="" o2max="" correspond="" with="" changes="" in="" sv,="" indicating="" a="" close="" link="" between="" the=""></ 0.05). conclusions:: high-aerobic intensity endurance interval training is significantly more effective than performing the same total work at either lactate threshold or at 70% hrmax, in improving v o2max. the changes in v o2max correspond with changes in sv, indicating a close link between the two.">

http://jp.physoc.org/cgi/reprint/575/3/901 here is a working link to the "SIT" study in pdf form.