Dr Mel Siff on Strength due to Muscle Tension or Metabolic Change?

Author: Dr Mel Siff Blog  //  Category: Main Content


While improvement in cardiovascular endurance almost exclusively is discussed
in terms of metabolic factors, increases in strength and hypertrophy are
discussed in terms of force generation and metabolic changes. Are these
changes more dependent on tension increase or on metabolic cost? The
following papers show that both of these factors appear to play an important
role in the development of strength and muscle hypertrophy, with the
specific type of training determining the outcome.


The role of metabolites in strength training. I. A comparison of eccentric and
concentric contractions.

Smith RC & Rutherford OM

Eur J Appl Physiol 1995;71(4):332-6

This study examined the role of high forces versus metabolic cost in the
adaptations following strength training. Ten young, healthy male and female
subjects trained one leg using concentric (CL) and the other using eccentric
(EL) contractions of the quadriceps muscle for 20 weeks. EL used weights
which were 35% higher than those used for CL. Isometric strength, and the
length-tension and force-velocity relationship of the muscle were measured
before and after training. Muscle cross-sectional area (CSA) was measured
near the knee and hip using computed tomography.

Increases in isometric strength were greater for CL (concentric leg)
compared to EL (eccentric leg), the difference being significant with the
knee at 90 degrees [mean (SD), 43.7 (19.6)% vs 22.9 (9.8)%, respectively].

Increases in isokinetic strength tended to be larger for EL, although the
differences were not significant. Significant increases in CSA occurred near
the hip for both EL and CL.

These results suggest that metabolic cost, and not high forces alone, are
involved in the stimuli for muscle hypertrophy and strength gains following
high-resistance training.


The role of metabolites in strength training. II. Short versus long isometric

Schott J, McCully K, Rutherford OM

Eur J Appl Physiol 1995;71(4):337-41

The role of intramuscular metabolite changes in the adaptations following
isometric strength training
was examined by comparing the effect of short, intermittent contractions (IC)
and longer,
continuous (CC) contractions. In a parallel study, the changes in phosphate
metabolites and pH were
examined during the two protocols using whole-body nuclear magnetic resonance
spectroscopy (NMRS).

Seven subjects trained three time per week for 14 weeks. The right leg was
trained using four sets of
ten contractions, each lasting 3 secs with a 2 sec rest period between each
contraction and 2 min between
each set. The left leg was trained using four 30 sec contractions with a 1 min
rest period between each.
Both protocols involved isometric contractions at 70% of a maximum voluntary
isometric contraction
(MVC). The MVC, length-tension and force-velocity relationships and
cross-sectional area (CSA) of each
leg were measured before and after training.

The increase in isometric strength was significantly greater for the continuous
(CC) contractions leg
(median 54.7%) than for the intermittent contractions (31.5%). There were no
significant differences
between the two protocols for changes in the length-tension or force-velocity
relationships. There were
significant increases in muscle CSA for the continuous (CC) contractions leg
only. NMRS demonstrated that
the changes in phosphate metabolites and pH were greater for the continuous
contractions protocol.

These findings suggest that factors related to the greater metabolite changes
during continuous (CC)
contractions training results in greater increases in isometric strength and
muscle CSA.

Dr Mel Siff
Denver, USA

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