title: Influence of short-term unweighing and reloading on running kinetics and muscle activity.
abstract: OBJECTIVE
  In running, body weight reduction is reported to result in decreased lower limb muscle activity with no change in the global activation pattern (Liebenberg et al. in J Sports Sci 29:207-214). Our study examined the acute effects on running mechanics and lower limb muscle activity of short-term unweighing and reloading conditions while running on a treadmill with a lower body positive pressure (LBPP) device.
  
  
  METHODS
  Eleven healthy males performed two randomized running series of 9 min at preferred speed. Each series included three successive running conditions of 3 min [at 100 % body weight (BW), 60 or 80 % BW, and 100 % BW]. Vertical ground reaction force and center of mass accelerations were analyzed together with surface EMG activity recorded from six major muscles of the left lower limb for the first and last 30 s of each running condition. Effort sensation and mean heart rate were also recorded.
  
  
  RESULTS
  In both running series, the unloaded running pattern was characterized by a lower step frequency (due to increased flight time with no change in contact time), lower impact and active force peaks, and also by reduced loading rate and push-off impulse. Amplitude of muscle activity overall decreased, but pre-contact and braking phase extensor muscle activity did not change, whereas it was reduced during the subsequent push-off phase.
  
  
  CONCLUSIONS
  The combined neuro-mechanical changes suggest that LBPP technology provides runners with an efficient support during the stride. The after-effects recorded after reloading highlight the fact that 3 min of unweighing may be sufficient for updating the running pattern.
authors.affiliation: Aix Marseille Université, CNRS, ISM UMR 7287, 13288, Marseille, France, patrick.sainton@univ-amu.fr.
authors.forename: Patrick
authors.initials: P
authors.lastname: Sainton
authors.forename: Caroline
authors.initials: C
authors.lastname: Nicol
authors.forename: Jan
authors.initials: J
authors.lastname: Cabri
authors.forename: Joëlle
authors.initials: J
authors.lastname: Barthelemy-Montfort
authors.forename: Eric
authors.initials: E
authors.lastname: Berton
authors.forename: Pascale
authors.initials: P
authors.lastname: Chavet
mesh_terms: D000054:Acceleration; D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena / Q000502:physiology; D001835:Body Weight / Q000502:physiology*; D004576:Electromyography; D005080:Exercise Test; D006801:Humans; D007700:Kinetics; D008297:Male; D012420:Running / Q000502:physiology*; D016474:Weight-Bearing / Q000502:physiology*; D055815:Young Adult