What functions do reflexes serve during human locomotion?

Zehr, E.P., and Stein, R.B. (1999). What functions do reflexes serve
during human locomotion? Prog. Neurobiol. 58(2):185-205.

Abstract

Studies on the reflex modulation of vertebrate locomotion have been
conducted in many different laboratories and with many different
preparations: for example, lamprey swimming, bird flight, quadrupedal
walking in cats and bipedal walking in humans. Emerging concepts are
that reflexes are task-, phase- and context-dependent. To function
usefully in a behavior such as locomotion wherein initial conditions
change from step to step, reflexes would have to show modulation. Papers
are reviewed in which the study of different reflexes have been
conducted during different behaviors, with an emphasis on experiments
in humans. A framework is developed in which the modulation
and flexibility of reflexes are demonstrated. Alterations in cutaneous,
and muscle (stretch and load receptor) reflexes between sitting,
standing and walking are discussed. Studies in which both electrical,
mechanical and `natural' receptor activation have been conducted during
walking are reviewed. Reflexes are shown to have important regulatory
functions during human locomotion. A framework for discussion of reflex
function throughout the step cycle is developed. The function of a given
reflex pathway changes dynamically throughout the locomotor cycle. While
all reflexes act in concert to a certain extent, generally cutaneous
reflexes act to alter swing limb trajectory to avoid stumbling and
falling. Stretch reflexes act to stabilize limb trajectory and assist
force production during stance. Load receptor reflexes are shown to
have an effect on both stance phase body weight support and step cycle
timing. After neurotrauma or in disease, reflexes no longer function as
during normal locomotion, but still have the potential to be clinically
exploited in gait modification regimens.

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similar studies of interest:

Zehr, E.P. (2005) Neural control of rhythmic human movement: the common
core hypothesis. Exercise and Sport Sciences Reviews 33:54-60

Zehr, E.P., Duysens, J. (2004) Regulation of arm and leg movement during
human locomotion. The Neuroscientist 10(4): 347-361

Frigon, A.F., Collins, D.F., and Zehr, E.P. (2004) Effect of arm
movement on reflexes in the legs: modulation of soleus H-reflexes and
somatosensory conditioning. J Neurophysiol. 91:1516-1523.

Haridas, C., and Zehr, E.P. (2003) Coordinated interlimb compensatory
responses to electrical stimulation of cutaneous nerves in the hand and
foot during walking. J Neurophysiol 90:2850-2861.