title: Different ankle muscle coordination patterns and co-activation during quiet stance between young adults and seniors do not change after a bout of high intensity training.
abstract: BACKGROUND
  Available evidence suggests that young adults and seniors use different strategies to adjust for increasing body sway during quiet standing. Altered antagonist muscle co-activation and different ankle muscle coordination patterns may account for this finding. Consequently, we aimed at addressing whether aging leads to changes in neuromuscular coordination patterns as well as co-activation during quiet stance. We additionally investigated whether a bout of high intensity interval training additionally alters these patterns.
  
  
  METHODS
  Twenty healthy seniors (age: 70 ± 4 y) and twenty young adults (age: 27 ± 3 y) were enrolled in the present study. In between the testing procedures, four consecutive high-intensity intervals of 4 min duration at a target exercise intensity of 90 to 95% HRmax were completed on a treadmill. The total center of pressure (COP) path length displacement served as standing balance performance outcome. In order to assess ankle muscle coordination patterns, amplitude ratios (AR) were calculated for each muscle (e.g. tibialis anterior (TA) [%] = (TA × 100)/(gastrocnemius medialis (GM) + soleus (SOL) + peroneus longus (PL) + TA). The co-activation was calculated for the SOL and TA muscles computing the co-activation index (CAI = 2 × TA/TA + SOL).
  
  
  RESULTS
  Seniors showed an inverted ankle muscle coordination pattern during single limb stance with eyes open (SLEO), compared to young adults (rest: GM, S: 15 ± 8% vs Y: 24 ± 9%; p = 0.03; SOL, S: 27 ± 14% vs Y: 37 ± 18%; p = 0.009; TA, S: 31 ± 13% vs Y: 13 ± 7%; p = 0.003). These patterns did not change after a high-intensity training session. A moderate correlation between amplitude ratios of the TA-contribution and postural sway was observed for seniors during SLEO (r = 0.61). Ankle co-activation was twofold elevated in seniors compared to young adults during SLEO (p < 0.001). These findings were also not affected by high intensity training.
  
  
  CONCLUSIONS
  Increased ankle co-activation in the anterior-posterior plane and inverted ankle muscle coordination pattern merely occurred during single-leg stance. Seniors with decreased postural control showed higher TA contributions during SLEO. These neuromuscular changes are not affected by acute intermittent high intensity aerobic exercise.
authors.affiliation: Department of Sport, Exercise and Health, University of Basel, Birsstrasse 320-B, 4052, Basel, Switzerland. lars.donath@unibas.ch.
authors.forename: Lars
authors.initials: L
authors.lastname: Donath
authors.affiliation: Department of Sport, Exercise and Health, University of Basel, Birsstrasse 320-B, 4052, Basel, Switzerland. eduard.kurz@med.uni-jena.de.|Clinic for Trauma, Hand and Reconstructive Surgery, Division of Motor Research, Pathophysiology and Biomechanics, Jena University Hospital, Bachstrasse 18, 07743, Jena, Germany. eduard.kurz@med.uni-jena.de.
authors.forename: Eduard
authors.initials: E
authors.lastname: Kurz
authors.affiliation: Department of Sport, Exercise and Health, University of Basel, Birsstrasse 320-B, 4052, Basel, Switzerland. ralf.roth@unibas.ch.
authors.forename: Ralf
authors.initials: R
authors.lastname: Roth
authors.affiliation: Department of Sport, Exercise and Health, University of Basel, Birsstrasse 320-B, 4052, Basel, Switzerland. lukas.zahner@unibas.ch.
authors.forename: Lukas
authors.initials: L
authors.lastname: Zahner
authors.affiliation: Department of Sport, Exercise and Health, University of Basel, Birsstrasse 320-B, 4052, Basel, Switzerland. oliver.faude@unibas.ch.
authors.forename: Oliver
authors.initials: O
authors.lastname: Faude
mesh_terms: D000058:Accidental Falls / Q000517:prevention & control*; D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology; D000842:Ankle; D000843:Ankle Joint / Q000502:physiology / Q000503:physiopathology; D004576:Electromyography / Q000379:methods; D015444:Exercise / Q000502:physiology; D005080:Exercise Test / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology / Q000503:physiopathology; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology; D013997:Time Factors