The effect of hand-held weights on the physiological responses to walking exercise.

To study the physiological responses to walking with hand-held weights (HWs), 12 untrained men completed three sub-maximal and two maximal treadmill tests. Heart rate, oxygen uptake, respiratory exchange ratio, ventilation, systolic blood pressure (BP), diastolic BP, rate pressure product, and rating of perceived exertion were significantly greater (P less than 0.01) when HWs were added to walking exercise performed at constant treadmill speed and grade. To evaluate whether the evaluated BP response was caused by HWs independent of exercise load, heart rate was held constant at 75% maximum heart rate reserve during the third submaximal test. Systolic BP (151.1 +/- 15.3 mm Hg vs 160.1 +/- 16.9 mm Hg) and rate pressure product (252.1 +/- 27.0 vs 237.3 +/- 25.1) were significantly greater (P less than 0.05) during exercise with HWs. Physiological responses to maximal exercise with and without 3 lb HWs were similar. The time to exhaustion, however, was reduced (P less than 0.01) with HWs. (719.3 +/- 98.1 s with HWs vs 784.4 +/- 118.9 s without HWs). These data indicate that 3-lb HWs can increase the metabolic cost of training (1 MET, 7 to 13 b X min-1) and may be useful in exercise prescription for individuals who do not want to run or are limited in the speed at which they can walk. Due to the exaggerated BP response, caution should be used when prescribing HW exercise for patients where increasing afterload may be a problem.

Learned interaction of visual and idiothetic cues in the control of place field orientation.

In a symmetrical environment (like a square box) hippocampal place cells use a mixture of visual and idiothetic (movement) information to tell them which way the environment is oriented. The present experiment tested the hypothesis that if the visual landmarks were mobile, place cells would learn to disregard these and rely on idiothetic cues instead. Place cells were recorded in a square box surrounded by circular black curtains. A cue card hung on the curtain behind one of the walls to break the fourfold symmetry. The relative influence of this card on the location of place fields was assessed each day by confining the rat on a rotating platter underneath an opaque cover, and then rotating the card and the platter by different amounts, to see whether subsequently recorded place fields had rotated with the card or with the rat. For some rats, these trials had been preceded by trials in which the card had been visibly moved from trial to trial, so that the rats had seen that it was mobile. Other rats received no prior visual information that the card was mobile. In the rats that had previously seen the card move, place fields initially rotated with the card but by the end of five sessions usually rotated with the rat instead. For rats that had never seen the card move, place fields always followed the card. Thus, the cells were able to "learn" that their preferred directional input, the card, was unreliable. A third group of rats, who were covered only for 30 s while the card was moved, showed mixed behaviour, suggesting a degradation of the idiothetic trace with time.

Directional control of hippocampal place fields.

Pyramidal cells in the rat hippocampus fire whenever the animal is in a particular place, suggesting that the hippocampus maintains a representation of the environment. Receptive fields of place cells (place fields) are largely determined by the distance of the rat from environmental walls. Because these walls are sometimes distinguishable only by their orientation with respect to the outside room, it has been hypothesised that a polarising directional input enables the cells to locate their fields off-centre in an otherwise symmetrical environment. We tested this hypothesis by gaining control of the rat's internal directional sense, independently of other cues, to see whether manipulating this sense could, by itself, produce a corresponding alteration in place field orientation. Place cells were recorded while rats foraged in a rectangular box, in the absence or presence of external room cues. With room cues masked, slow rotation of the rat and the box together caused the fields to rotate accordingly. Rotating the recording box alone by 180 degrees rarely caused corresponding field rotation, while rotating the rat alone 180 degrees outside the environment and then replacing it in the recording box almost always resulted in a corresponding rotation of the fields. This shows that place field orientation can be controlled by controlling the internal direction-sense of the rat, and it opens the door to psycho-physical exploration of the sensory basis of the direction sense. When room cues were present, distal visual cues predominated over internal cues in establishing place field orientation.