Yet, opposite findings have also been reported ( Kay et al., 1975), as well as increased respiratory rates during mental imagery of exercise, that is without actual movements ( Thornton et al., 2001).
Firstly, breathing augmentation during running is often considered to be inherently proportional to the velocity of repetitive limb movements ( Bechbache and Duffin, 1977 Eldridge et al., 1981 DiMarco et al., 1983 Casey et al., 1987). Two alleged signatures of hyperpnoea to running exercise have in particular fueled this model.
Despite this, a common postulate is that respiratory frequency is entrained by that of locomotor movements, through inertial oscillations of the viscera and/or by proprioceptive signals from the limbs impacting the respiratory generator ( Iscoe and Polosa, 1976 Bramble and Carrier, 1983 Baudinette et al., 1987 Alexander, 1993 Morin and Viala, 2002 Potts et al., 2005 Giraudin et al., 2012). While examining the dynamic interactions between respiratory and locomotor movements should inform on the origin and nature of the activatory signal, studies have failed to reveal regularities. The hyperpnoea during running is principally supported by an increased respiratory rate which underscores an upregulation of the respiratory rhythm generator in the brainstem ( Del Negro et al., 2018). Probably, the most striking example is the augmentation of ventilation at the transition from rest to running exercise to match the augmented energetic demand ( Bramble and Carrier, 1983 Mateika and Duffin, 1995 Gariépy et al., 2010). The versatile adaptability of breathing to changes in the environment or behavioral state is vital. Our work thus highlights that exercise hyperpnoea can operate, at least in mice and in the presently examined running regimes, without phasic constraints from limb movements. However, we found no temporal coordination of breaths to strides at any speed, intensity, or gait. Respiratory rate was yet further increased during escape-like running and most particularly at gallop. We show that, for a wide range of trotting speeds on a treadmill, respiratory rate increases to a fixed and stable value irrespective of trotting velocities. Here, we examined respiratory changes during running in the resourceful mouse model.
In particular, whether breathing frequency is inherently proportional to limb velocity and imposed by a synchronization of breaths to strides is still unclear.
However, studies have failed to reveal regularities. Examining whether and how the rhythms of limb and breathing movements interact is highly informative about the mechanistic origin of hyperpnoea during running exercise.