title: Positive versus negative foot inclination for maximum height two-leg vertical jumps.
abstract: OBJECTIVE
  To test the hypothesis that a negative foot inclination can increase vertical jump height; to determine if an optimal degree of foot inclination exists; to design an athletic shoe based on our findings and determine the effect of the design on jump height.
  
  
  BACKGROUND
  A number of inventors claim that athletic shoes that incorporate a negative foot inclination (the heel being lower than the fore-foot) can enhance athletic performance.
  
  
  METHODS
  This study was conducted in three phases. Using an adjustable wooden platform to vary the foot inclination, phase one tested standing two-leg jumps at +4, 0, -2, -3, -4 degrees of inclination. Using the same procedures, phase two tested running two-leg jumps comparing +4 degree inclination (standard shoe) with -3.5 degrees ('optimal' angle from phase one). In phase three, actual -3.5 degree prototype shoes were fabricated and compared to +4 degree standard athletic shoes.
  
  
  METHODS
  Since each subject was tested at all angles, the appropriate statistical design was repeated measures. In phase one, since there were five angles, F-testing was used in the analysis, while in phases two and three, since only two angles were used, paired t-tests were used.
  
  
  RESULTS
  The results of phase three showed that all ten jumpers improved their jump height when using the -3.5 degree prototype shoe. The average increase was 4.8cm, a 10% increase on average, with the minimum increase being 2.4cm. Similar results were found for both phase one and for phase two testing.
  
  
  CONCLUSIONS
  In conclusion, we have found convincing evidence that negative foot inclination increases jump height in two-leg vertical jumps.
  
  
  CONCLUSIONS
  Coaches and athletes may want to pursue any findings that suggest they might improve performance and athletic trainers will want to know what negative effects might be introduced by an athletic shoe using this design. Besides the possibility of negative effects, clinicians will also be interested in whether musculo-skeletal adaptations will negate the effect. Finally, biomechanists will want to know what mechanism is causing the increase in jump height.
authors.affiliation: 510 Pearl Street, Ypsilanti, USA. engharris@online.emich.edu
authors.forename: C
authors.initials: C
authors.lastname: Larkins
authors.forename: T E
authors.initials: TE
authors.lastname: Snabb
mesh_terms: D000293:Adolescent; D000328:Adult; D004867:Equipment Design; D005260:Female; D005528:Foot; D006801:Humans; D008297:Male; D012775:Shoes; D013177:Sports / Q000502:physiology