title: Perceived loading and muscle activity during hip strengthening exercises: comparison of elastic resistance and machine exercises.
abstract: OBJECTIVE
  Decreased hip muscle strength is frequently reported in patients with hip injury or pathology. Furthermore, soccer players suffering from groin injury show decreased strength of hip muscles. Estimating 10-repetition maximum can be time-consuming and difficult, thus, using the Borg category rating 10 scale (Borg CR10 scale) can be a useful tool for estimating the intensity of exercise. The aims of this study were 1) to investigate the feasibility of the use of the Borg CR10 scale for rating strength training intensity of the hip abductor and hip adductor muscles, and 2) to compare hip muscle activity during hip abduction and hip adduction exercises using elastic resistance and isotonic machines, using electromyography (EMG).
  
  
  METHODS
  EMG activity was recorded from 11 muscles at the hip, thigh and trunk during hip adduction and hip abduction exercises in 16 untrained women, using elastic resistance and isotonic exercise machines. These recordings were normalized to maximal voluntary contraction (MVC) EMG (nEMG). The exercises were performed at four levels of perceived loading reported using the Borg CR10: light (Borg ≤2), moderate (Borg >2-<5), heavy (Borg ≥5-<7) and near maximum (Borg ≥7).
  
  
  RESULTS
  Moderate to strong associations were observed between perceived loading and nEMG obtained during the adduction exercise with elastic resistance (r=0.8±0.3) as well as in machine (r=0.69±0.55) and the abduction exercise with elastic resistance (r=0.66±0.29) as well as in machine (r =0.62±0.54). The abduction exercise performed with elastic resistance displayed significantly higher gluteus medius nEMG recruitment than the in machine exercise.
  
  
  CONCLUSIONS
  The results of this study show that the Borg CR10 scale can be a useful tool for estimating intensity levels during resistance training of the hip adductor and hip abductor muscles. Although elastic resistance and exercise machine seem equally effective for recruiting muscle activity of the hip adductors, the elastic resistance condition was able to demonstrate greater muscle recruitment than the exercise machine during hip abduction.
authors.affiliation: National Research Centre for the Working Environment Copenhagen, Denmark.
authors.forename: Mikkel
authors.initials: M
authors.lastname: Brandt
authors.forename: Markus Due
authors.initials: MD
authors.lastname: Jakobsen
authors.affiliation: Arthroscopic Centre Amager, Amager University Hospital, Copenhagen, Denmark.
authors.forename: Kristian
authors.initials: K
authors.lastname: Thorborg
authors.forename: Emil
authors.initials: E
authors.lastname: Sundstrup
authors.forename: Kenneth
authors.initials: K
authors.lastname: Jay
authors.affiliation: National Research Centre for the Working Environment Copenhagen, Denmark.
authors.forename: Lars L
authors.initials: LL
authors.lastname: Andersen
keywords: Elastic resistance; hip abduction; hip adduction; strength training