title: The influence of upper body fatigue on dynamic standing balance.
abstract: OBJECTIVE
  Muscle fatigue is related to a decline in force output and proprioception. These can ultimately have an adverse effect on neuromuscular control and functional performance. Local muscle fatigue has been shown to have adverse consequences on dynamic standing balance; however, much less is known regarding the relationship between distant fatigue and dynamic standing. The purpose of this study was to investigate the effects of upper body fatigue on dynamic standing balance. It was hypothesized that distant fatigue in upper body musculature would show a significant decrease in dynamic standing balance as assessed by the Lower Quarter Y-Balance Test (YBT-LQ).
  
  
  METHODS
  TWENTY HEALTHY INDIVIDUALS (AGE: 25.0 ± 3.42 years, height: 172.72 ± 13.11 cm, mass: 71.36 ± 13.50 kg) participated in this study. A kayak ergometer was used to implement a fatigue protocol for the upper body. The protocol consisted of a graded intensity session ranging from 50% to 90% of maximum effort lasting ten minutes in duration (2 minutes each at 50% 60%, 70%, 80%, and 90%). The anterior (ANT), posteromedial (PM), and posterolateral (PL) reach directions were normalized to leg length and measured on the YBT-LQ before and after the fatigue protocol for each participant. A fourth value termed overall balance was calculated as the sum of the furthest reach distance of the three directions. Blood lactate analysis taken before and immediately after the fatigue protocol was used to quantify fatigue. Multiple paired t-tests were performed for pre-fatigue and post-fatigue balance assessment. A Bonferroni correction was applied to set the significance value ≤0.0125 a priori. Effect size was calculated using the effect size index.
  
  
  RESULTS
  Blood lactate values immediately following the fatigue protocol had an average concentration of 6.15 millimoles (pre: 2.3, post: 8.4). The ANT reach direction (ρ = 0.004) and the calculated overall balance (ρ = 0.011) significantly decreased post-fatigue in the dominant lower extremity. No significant differences were found for the PM (ρ = 0.017) or PL (ρ = 0.021) directions. The ANT reach direction (0.64) and overall balance (0.44) also showed a moderate effect size based on the effect size index.
  
  
  CONCLUSIONS
  ANT and overall dynamic standing balance were negatively affected after completing the upper body fatigue protocol. The findings of this research demonstrate that upper body fatigue has adverse effects on dynamic standing balance, as measured by performance on the YBT-LQ. Significant and clinically relevant differences were noted in ANT and overall dynamic standing balance.
  
  
  CONCLUSIONS
  Physical therapists should be aware of the adverse influence distant fatigue may exhibit on neuromuscular control in muscles not actively involved in the fatiguing exercise. The balance deficits noted may indicate an increased risk of injury with muscle fatigue in muscles not directly contributing to standing balance.
  
  
  METHODS
  3b, Case-control study.
authors.affiliation: East Tennessee State University, Department of Physical Therapy, Johnson City, TN, USA.
authors.forename: Craig A
authors.initials: CA
authors.lastname: Wassinger
authors.affiliation: East Tennessee State University, Department of Physical Therapy, Johnson City, TN, USA.
authors.forename: Hayley
authors.initials: H
authors.lastname: McKinney
authors.affiliation: East Tennessee State University, Department of Physical Therapy, Johnson City, TN, USA.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Roane
authors.affiliation: East Tennessee State University, Department of Physical Therapy, Johnson City, TN, USA.
authors.forename: Mary Jo
authors.initials: MJ
authors.lastname: Davenport
authors.affiliation: East Tennessee State University, Department of Physical Therapy, Johnson City, TN, USA.
authors.forename: Bea
authors.initials: B
authors.lastname: Owens
authors.affiliation: East Tennessee State University, Department of Physical Therapy, Johnson City, TN, USA.
authors.forename: Ute
authors.initials: U
authors.lastname: Breese
authors.affiliation: East Tennessee State University, Department of Physical Therapy, Johnson City, TN, USA.
authors.forename: Geri Ann
authors.initials: GA
authors.lastname: Sokell
keywords: Distant fatigue; Lower Quarter Y‐Balance Test; dynamic standing balance