Preferred and optimal stride frequency, stiffness and economy: changes with fatigue during a 1-h high-intensity run

Abstract

Metabolic cost of submaximal running at constant speed is influenced by various factors including fatigue and kinematic characteristics. Metabolic costs typically drift upwards during extended running while stride characteristics often shift away from initial. When non-fatigued, experienced runners naturally optimize stride frequency in a manner that minimizes oxygen uptake. An initial objective was to determine whether runners demonstrate a similar self-optimizing capability when fatigued where stride characteristics have perhaps shifted away from the initial state. A secondary objective involved measurement of vertical and leg stiffness characteristics as a potential explanation for frequency changes with fatigue. We hypothesized that runners decrease stride frequency and stiffness with fatigue while optimizing these characteristics to minimize metabolic cost. Sixteen experienced runners completed a near maximal effort 1-h treadmill run at a constant speed. Preferred and optimal stride frequencies (PSF and OSF) were measured near the beginning and end of the hour run using frequencies +/-4 and +/-8% around PSF. From vertical force data recorded throughout the run, leg and vertical stiffness were determined. As expected, oxygen uptake significantly increased during the run from 45.9 to 47.4 ml kg(-1) min(-1) (P = 0.004). There was no difference between preferred and optimal stride frequencies at the beginning or the end of running (P = 0.978), however both PSF and OSF significantly decreased from 1.45 to 1.43 Hz (P = 0.026). All runners self-optimized stride frequency at the beginning and end of one-hour of running despite changes of optimal stride frequency. Stiffness and stride frequency changes were subject specific with some runners exhibiting little to no change. No clear relationship of frequency or stiffness changes to economy was found.

Altered neuromuscular control of leg stiffness following soccer-specific exercise

“…In agreement with previous research of group responses to one hour of continuous running (Hunter and Smith 2007) and exercise replicating a soccer match (Cone et al 2012), leg stiffness was found not to significantly change following the soccer-specific exercise. In the present study half of the participants increased, while the other half decreased, their leg stiffness following exercise.…”

“…Those authors reported no significant change in the group stiffness response post soccer-match, however individual responses or potential changes in neuromuscular control with fatigue were not considered. Following exhaustive running, leg stiffness is known to decrease (Dutto and Smith 2002), whereas, following non-exhaustive prolonged running changes to stiffness have been reported to be individualised (Hunter and Smith 2007). Given the non-exhaustive nature of soccer it may be speculated that changes to leg stiffness during a match will be playerspecific, with players who exhibit fatigue-induced decrements in stiffness at risk of impaired joint stability (Hughes and Watkins 2008) and increased stress on passive structures resulting in increased injury risk (Dutto and Smith, 2002).…”

An adaptive and robust online method to predict gait events

“…Furthermore, they are suboptimal when fatigue could affect stride time in long experimental protocols. This effect has been reported in running [8], [9] and could apply to walking as well. An altered stride time would deteriorate the precision of constant preset delays and thus, the timing of external interventions.…”

“…This could, however, be different for longer protocols, as fatigue has been shown to cause cadence changes in running [8], [9].…”

Lower Limb Mechanical Properties: Significant References Omitted

“…Research into how vertical or leg stiffness are altered with fatigue during or after short-(i.e. repeated sprint [14][15][16][17]), moderate- [18][19][20][21] or long-duration runs (i.e. several hours [22,23]) is undergoing unprecedented popularity.…”