Dose-response relationship between interval training frequency and magnitude of improvement in lactate threshold.

The purpose of this study was to determine if interval training at 110-120% of peak power output one and two days/wk in addition to habitual training would elicit improvements in lactate threshold (LT) in a dose response manner. Twenty physically active individuals completed this study: age--21.1+/-1.3 yr, height--172.1+/-7.4 cm, body mass--68.4+/-9.1 kg, VO (2)max--45.3+/-5.2 mL/kg/min; and were randomly assigned into two separate 6 wk training groups--either 1 day/wk interval training or 2 days/wk interval training at 110-120% of peak workload (from an incremental exercise test) on a cycle ergometer. After 6 wk, LT (% VO (2)max) increased significantly ( P<0.05) in both 1 day/wk (4.3+/-3.2%) and 2 days/wk (8.2+/-2.6%) groups. A two-factor mixed ANOVA identified a significant interaction between exercise frequency and LT (%VO (2)max) values ( P<0.05) indicating that LT responded differently to 1 day/wk and 2 days/wk of interval training. Findings from the present study show high-intensity, interval training to be a successful strategy for modifying this important metabolic threshold. Moreover, results suggest that there is a dose-response relationship between frequency of interval training and the magnitude of LT improvement.

Retrieval of information from multiple ensembles in short-term memory.

A recognition memory experiment investigated Ss' ability to organize information in short-term memory. A paradigm similar to that used by Sternberg was employed. A sequentially presented series of six digits (positive set) was shown with each digit appearing on a red, green, or amber background. The colors defined different ensembles, and responding to a test digit was contingent upon an item's membership in the positive set and the color-defined ensemble. Reaction time (RT) to the test digits indicated that Ss did organize information into ensembles. Furthermore, when informative cues were presented prior to the test item, Ss directed and confined their search to the cued subset.

Seasonal changes in brain GnRH immunoreactivity and song-control nuclei volumes in an opportunistically breeding songbird.

White-winged crossbills (Loxia leucoptera) are opportunistic breeders that can nest at almost any time of year if there is sufficient food. Other cardueline finches that have been shown to breed on a strictly seasonal schedule become absolutely refractory to the stimulatory effects of long-day photoperiod, dramatically down-regulate hypothalamic gonadotropin-releasing hormone (GnRH), and reduce the volume of several song-control nuclei in autumn. This study examined whether changes in photoperiod modify the GnRH and song-control systems in white-winged crossbills. Adult male and female crossbills were captured and held on a naturally changing photoperiod. Brains of male and female birds were collected in May, October, and January. GnRH content was assessed by immunocytochemistry and the volumes of Nissl-defined song-control nuclei (HVc, Area X, and the robust nucleus of the archistriatum) were reconstructed. In contrast to other cardueline finches, GnRH immunoreactivity was relatively stable across the year, exhibiting only modest seasonal variation. The song control system, on the other hand, exhibited large seasonal changes as well as sex differences. Thus, crossbills appear to maintain hypothalamic GnRH content year round, perhaps to facilitate a rapid response to favorable breeding conditions, even on short days. However, song control nuclei are dramatically affected by photoperiod. Future work should examine these systems in crossbills breeding on short days to compare photoperiod-dependent and -independent effects on neural plasticity.