title: Grip and load force coordination in cyclical isometric manipulation task is not affected by the feedback type.
abstract: BACKGROUND
  The relationship between normal and tangential force components (grip force - GF and load force - LF, respectively) acting on the digits-object interface during object manipulation reveals neural mechanisms involved in movement control. Here, we examined whether the feedback type provided to the participants during exertion of LF would influence GF-LF coordination and task performance.
  
  
  METHODS
  Sixteen young (24.7 ±3.8 years-old) volunteers isometrically exerted continuously sinusoidal F(Z) (vertical component of LF) by pulling a fixed instrumented handle up and relaxing under two feedback conditions: targeting and tracking. In targeting condition, F(Z) exertion range was determined by horizontal lines representing the upper (10 N) and lower (1 N) targets, with frequency (0.77 or 1.53 Hz) dictated by a metronome. In tracking condition, a sinusoidal template set at similar frequencies and range was presented and should be superposed by the participants' exerted F(Z). Task performance was assessed by absolute errors at peaks (AE(Peak)) and valleys (AE(Valley)) and GF-LF coordination by GF-LF ratios, maximum cross-correlation coefficients (r(max)), and time lags.
  
  
  RESULTS
  The results revealed no effect of feedback and no feedback by frequency interaction on any variable. AE(Peak) and GF-LF ratio were higher and r(max) lower at 1.53 Hz than at 0.77 Hz.
  
  
  CONCLUSIONS
  These findings indicate that the type of feedback does not influence task performance and GF-LF coordination. Therefore, we recommend the use of tracking tasks when assessing GF-LF coordination during isometric LF exertion in externally fixed instrumented handles because they are easier to understand and provide additional indices (e.g., RMSE) of voluntary force control.
authors.affiliation: Institute of Physical Activity and Sport Sciences and Graduate Program in Human Movement Sciences, Cruzeiro do Sul University, Rua Galvão Bueno 868, 13° andar, Bloco B, São Paulo 01506-000, SP, Brazil.
authors.forename: Sabrina Tiago
authors.initials: ST
authors.lastname: Pedão
authors.forename: José Angelo
authors.initials: JA
authors.lastname: Barela
authors.forename: Kauê Carvalho de Almeida
authors.initials: KC
authors.lastname: Lima
authors.forename: Paulo Barbosa
authors.initials: PB
authors.lastname: de Freitas
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001696:Biomechanical Phenomena / Q000502:physiology*; D003627:Data Interpretation, Statistical; D025461:Feedback, Physiological / Q000502:physiology*; D005260:Female; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D011597:Psychomotor Performance / Q000502:physiology; D014160:Transducers, Pressure; D016474:Weight-Bearing; D055815:Young Adult
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