Oxygen Consumption of Elite Distance Runners on an Anti-Gravity Treadmill?

Lower body positive pressure (LBPP), or ‘anti-gravity’ treadmills® have become increasingly popular among elite distance runners. However, to date, few studies have assessed the effect of body weight support (BWS) on the metabolic cost of running among elite runners. This study evaluated how BWS influenced the relationship between velocity and metabolic cost among 6 elite male distance runners. Participants ran three- 16 minute tests consisting of 4 stages of 4 minutes at 8, 7, 6 and 5 min·mile⁻¹ pace (3.35, 3.84, 4.47 and 5.36 m·s⁻¹), while maintaining an aerobic effort (Respiratory Exchange Ratio ≤1.00). One test was run on a regular treadmill, one on an anti-gravity treadmill with 40% BWS and one with 20% BWS being provided. Expired gas data were collected and regression equations used to determine and compare slopes. Significant decreases in oxygen uptake (V̇O₂) were found with each increase in BWS (p < 0.001). At 20% BWS, the average decrease in net VO2 was greater than proportional (34%), while at 40% BWS, the average net reduction in VO₂ was close to proportional (38%). Across velocities, the slope of the relationship between VO₂ and velocity (ΔV̇O₂/Δv) was steeper with less support. The slopes at both the 20% and 40% BWS conditions were similar, especially when compared to the regular treadmill. Variability in VO₂ between athletes was much greater on the LBPP treadmill and was greater with increased levels of BWS. In this study we evaluated the effect of body weight support on V̇O₂ among elite distance runners. We have shown that oxygen uptake decreased with support, but not in direct proportion to that support. Further, because of the high variability in oxygen uptake between athletes on the LBPP treadmill, prediction equations may not be reliable and other indicators (heart rate, perceived exertion or directly measured oxygen uptake) should be used to guide training intensity when training on the LBPP treadmill.

Key points

• With increasing amounts of body weight-support (BWS), the slope of the relationship between velocity and oxygen consumption (ΔVO₂/Δv) decreases significantly. This means the change in oxygen consumption (VO₂) is significantly smaller over a given change in velocity at higher amounts of BWS.
• There is a non-linear decrease in VO₂ with increasing BWS. As such, with each increment in the amount of BWS provided, the reduction in VO₂ becomes increasingly smaller.
• This paper provides first of its kind data on the effects of BWS on the cost of running among highly trained, elite runners. The outcomes of this study are in line with previous findings among non-elite runners.

Key words: AlterG®, anti-gravity treadmill®, distance running, elite, oxygen consumption, LBPP treadmill     

Age affects spontaneous activity and depolarizing afterpotentials in isolated gonadotropin-releasing hormone neurons

Neuronal activity underlying the pulsatile secretion of GnRH remains poorly understood, as does the endogenous generation of such activity. It is clear that changes at the level of the hypothalamus are taking place during reproductive aging, yet virtually nothing is known about GnRH neuronal physiology in aging and postreproductive animals. In these studies, we performed cell-attached and whole-cell recordings in GnRH-enhanced green fluorescent protein neurons dissociated from young (3 months), middle-aged (10 months), and old (15-18 months) female mice. All mice were ovariectomized; half were estradiol replaced. Neurons from all ages fired spontaneously, most in a short-burst pattern that is characteristic of GnRH neuronal firing. Membrane characteristics were not affected by age. However, firing frequency was significantly reduced in neurons from old animals, as was spike patterning. The amplitude of the depolarizing afterpotential, evoked by a 200-msec current pulse, was significantly smaller in aged animals. In addition, inward whole-cell currents were reduced in estradiol-treated animals, although they were not significantly affected by age. Because depolarizing afterpotentials have been shown to contribute to prolonged discharges of activity after a very brief excitatory input, a decreased depolarizing afterpotential could lead to attenuated pulses in older animals. In addition, decreases in frequency and pattern generation could lead to improper information coding. Therefore, changes in the GnRH neuron during aging could lead to dysregulated activity, potentially resulting in the attenuated LH pulses observed in the transition to reproductive senescence.