Resistance Training Effects on Muscle Morphological, Mechanical and Contractile Properties
Condition: Hypertrophy; Contraction
MeSH terms: Hypertrophy
Study type: Interventional

Summary: 
      The aim of the research project is to investigate the influence of resistance-training
      prescription (repetition duration, time under tension and training volume) and sex have on
      morpho-functional adaptations of upper and lower-body skeletal muscles. Twenty-four male and
      female university students were randomly assigned to one of two experimental groups, based on
      the repetition duration : "fast" group (with 1 second for eccentric and concentric phase) and
      "slow" group with prolonged duration of eccentric contraction (4 seconds for eccentric and 1
      second concentric phase). At baseline and final measurement, cross-section area,
      one-repetition maximum and tensiomyography parameters (contraction time - Tc and radial
      displacement - Dm) of elbow flexors (biceps brachii) and knee extensors (4 quadriceps
      muscles) were evaluated.
    

Detailed description: 
      Isotonic resistance training has been widely applied in sport and exercise. Design of
      resistance training programs depends on numerous training variables, such as intensity,
      volume, time under tension (TUT), repetition duration (tempo), etc. It has been shown that
      manipulation of repetition duration affects TUT and training volume, which in turn could
      results in distinct morphological and contractile adaptative response of skeletal muscle. The
      aim of the research was three-fold: i) to compare two different tempos of resistance
      exercise, which differ in the duration of eccentric phase on hypertrophy, strength and
      contractile properties of the elbow flexors and knee extensors muscles, ii) to compare
      sex-specific adaptations in hypertrophy, strength and contractile properties of the elbow
      flexors and knee extensors muscles produced by training intervention, iii) to investigate
      potential cause-and-effect association between changes in size, strength and contractile
      properties of the tested muscles.

      The subjects were assigned to two experimental groups, based on the duration of the eccentric
      muscle contraction in resistance training. All participants were fully informed about
      experimental procedures and potential risks and they signed written informed consent prior to
      participation in the study. The training intervention was performed twice per week for a
      7-week period. Before training intervention, a 2-week familiarization period was conducted.
      Elbow flexor and knee extensors muscle dimensions and strength were assessed 2 days before
      and after training intervention, while contractile properties were evaluated 5 days before
      and after experiment. The number of repetitions, training volume (number of repetitions x
      number of series), and TUT were recorded after first session of training intervention for
      both groups.

      Muscle strength was assessed by one-repetition maximum test (1RM) for two exercises: elbow
      flexion on Scott's bench and parallel barbell squat. Each participant had 5 attempts to lift
      the maximum weight with pauses between trials of 3 minutes.

      Muscles cross-section area (CSA) were evaluated by ultrasonic device (Siemens Antares,
      Erlangen, Germany), using the 2D ellipse diagnostic method with variable high frequency
      transducer (from 7 MHz to 13 MHz), for 5 muscles: elbow flexor (biceps brachii) and 4 knee
      extensors (rectus femoris , vastus intermedius, vastus medialis, vastus lateralis). The
      measurements were performed while the subjects seated with their elbows and knees extended
      and relaxed. The biceps brachii CSA was measured at two-thirds of the distance from the
      acromion to the antecubital crease. CSA of rectus femoris was measured at the height of
      proximal section of its distal third, above musculoskeletal joint. CSA of vastus intermedius
      and vastus medialis were measured at the height of distal part right above the patella. The
      visible part of vastus lateralis was measured at the distal third directly above the patella,
      under rectus femoris level.

      The contractile properties of biceps brachii, rectus femoris and vastus lateralis muscles
      were evaluated by tensiomyography according to the manufacturer's instructions (TMG-Science
      for Body Evaluation, Ljubljana, Slovenia). The values of contraction time (Tc) and radial
      deformation (Dm) were taken for analysis. The biceps brachii testing was performed while
      subjects were in a sitting position with the dominant arm bent at 90°. During the assessment
      of the knee extensors subjects were lying on the back, where dominant leg was placed on the
      support, forming a knee angle of 120°. Subjects were asked to perform a voluntary
      contraction, in order to mark the point of placement of the TMG sensor by the palpation
      method. Two self-adhesive electrodes (Pals Platinum, model 895220 with multi-stick gel,
      AxelGaard Manufacturing Co. Ltd) were placed proximal and distal at 3 cm from the marked
      point, emitting an electrical impulse. A sensor (GK40, Panoptik d.o.o., Ljubljana, Slovenia)
      was placed between the electrodes to detect muscle changes initiated by electrical
      stimulation. The initial impulse was 25 milliamperes (mA) and it increased proportionally by
      10 mA, until the maximum (muscle no longer responds to electrical stimulus).

      Both experimental groups performed two exercises to target elbow flexor and knee extensor
      muscles: biceps curl on a Scott bench and parallel barbell squat, respectively. All sessions
      were performed at the same time (13-15 h), with a minimum 48 h rest between sessions on the
      same days during the week. For both groups, the intensity of load (1RM%) and number of sets
      were as follows: in the first three weeks the subjects exercises with ̴ 60% of 1RM in 3 sets,
      while during the next four weeks the load was set at ̴ 70% of 1RM in 4 sets. The difference
      in training protocols was in the duration of the eccentric phase, where one group performed
      training with a tempo of 1 seconds for eccentric and concentric phase, while for other group
      tempo was 4 seconds for eccentric and 1 seconds for concentric phase. All repetitions were
      performed until muscular failure. The pause between sets was 2 minutes.

      Prior to analysis data were checked for normality and that the relevant assumptions for each
      test were met. Differences in the training volume and the TUT between the groups were
      determined by an independent t-test. One-way ANCOVA (using baseline values as covariates) was
      used to examine differences in changes of CSA, 1RM and TMG parameters between the groups. If
      ANCOVA showed statistical significance, the bonferroni post-hoc test was used for further
      estimation of differences between groups. Additionally, using sex as between-group factor and
      baseline values as covariates, ANCOVA was used to determine possible differences between
      males and females in changes of morphological, mechanical and contractile variables. Relative
      changes for each variable was derived from Pre to Post change in percentage, and for each
      participant. Pearson's correlation coefficient was used to examine the association between
      relative pre-to-post changes of CSA, 1RM and TMG for tested muscles. Data were reported as
      mean ± standard deviation. The level of significance was set at p < 0.05. The program used
      for statistical analysis was Statistical Package for Social Sciences (IBM SPSS Statistics),
      version 20.0.
    

Intervention name(s): resistance training
Intervention type(s): Other
Intervention description(s): Both experimental groups performed two exercises to target elbow flexor and knee extensor muscles: biceps curl on a Scott bench and parallel barbell squat, respectively. All sessions were performed at the same time (13-15 h), with a minimum 48 h rest between sessions on the same days during the week. For both groups, the intensity of load (1RM%) and number of sets were as follows: in the first three weeks the subjects exercises with ̴ 60% of 1RM in 3 sets, while during the next four weeks the load was set at ̴ 70% of 1RM in 4 sets. All repetitions were performed until muscular failure. The pause between sets was 2 minutes.
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Double (Investigator, Outcomes Assessor)
Primary purpose: Treatment