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Old 03-01-2009, 02:41 PM   #16
Donald Lee
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The below may be useful:

Zatsiorsky,V.M. (Editor).(2000). "Biomechanics in Sport. Performance
Enhancement and Injury Prevention." Blackwell Science Ltd: Malden, MA.
(ISBN-0-632-05392-5)
Chapter 4, "Eccentric Muscle Action in Sport and Exercise." Editor
B.I. Prilutsky.

The magnitude of maximum eccentric moments is substantially higher
than that of concentric moments (Fig. 4.7a). Since concentric moments
sharply decline with angular velocity and eccentric moments do not
decrease markedly, the difference in the magnitude between eccentric
and concentric moments becomes larger as absolute values
of angular velocity increase.
The hypothesis that eccentric exercises require fewer active muscle
fibres than concentric exercises with the same resistance (Abbot et
aI. 1952; Asmussen 1953) is supported by lower values of
the ratio electromyographic activity (EMG)/force (or the slope of EMG-
force relationship) in eccentric action compared with concentric
action
(Fig. 4.8a; actions appears to be similar (Fig. 4.7b; Rodgers
& Berger 1974; Komi & Viitasalo 1977; Seliger et al. 1980; Westing et
ai. 1990; however, see Enoka 1996).
Several authors have reported differences in motor unit behaviour
between eccentric and concentric actions (Nordone et al. 1989; Howell
et al. 1995; Enoka 1996): high-threshold motor units seem to be used
more extensively in eccentric actions than in concentric actions, and
the spike rate of the involved motor units is lower in eccentric
actions compared with concentric. A larger involvement of high-
threshold motor units in eccentric exercise is supported by the
observation that after intensive eccentric exercise, signs of muscle
fibre damage are seen more often in type II (fast-twitch) muscle
fibres (Friden et al. 1983), which are controlled by highthreshold
motor units.
An alternative explanation for a preferential injury of
fast-twitch muscle fibres in eccentric actions is that fast-twitch
fibres may be more susceptible to stretch-induced damage because of a
less-developed endomysium compared with slow-twitch fibres (Stauber
1989).

Is eccentric action more advantageous for isometric strength training
than isometric and concentric actions because higher muscle forces
can be produced during eccentric action? In most cases, eccentric
strength training does not lead to higher isometric strength and is
comparable with isometric
and concentric training
(Table 4.1). Even when
eccentric training is shown to be more effective for increasing
isometric strength, it often has sideeffects such as muscle injury
and soreness (for reviews, see Armstrong 1984; Prilutsky 1989; Friden
& Lieber 1992; see also Chapter 28). Therefore, it appears that
combining different types of exercise is a better method for strength
training. It should be noted that strength training may be action
type specific (Kellis & Baltzopoulos 1995)-eccentric training may
improve eccentric strength more than concentric (see e.g. Hortobagyi
et al. 1996b). Some studies, however, demonstrate similar
improvements in eccentric, isometric and concentric strength after
eccentric training (Kellis & Baltzopoulos 1995).

=========================

Adaptation to chronic eccentric exercise in humans: the influence
of contraction velocity.

Douglas Paddon-Jones, Michael Leveritt, Andrew Lonergan , Peter
Abernethy

We compared changes in muscle fibre composition and muscle strength
indices
following a 10 week
isokinetic resistance training programme consisting of fast (3.14
rad.s-1) or
slow (0.52 rad.s-1) velocity eccentric
muscle contractions. A group of 20 non-resistance trained subjects
were assigned
to a FAST (n=7),
SLOW (n=6) or non-training CONTROL (n=7) group. A unilateral training
protocol targeted the elbow flexor muscle group and consisted of 24
maximal eccentric isokinetic contractions (four sets of six
repetitions)
performed three times a week for 10 weeks. Muscle biopsy samples were
obtained from the belly of the biceps brachii. Isometric torque and
concentric and eccentric torque at 0.52 and 3.14 rad.s-1 were
examinedat 0, 5
and 10 weeks.

After 10 weeks, the FAST group demonstrated
significant [mean (SEM)] increases in eccentric [29.6 (6.4)%] and
concentric torque [27.4 (7.3)%] at 3.14 rad.s-1, isometric torque
[21.3
(4.3)%] and eccentric torque [25.2 (7.2)%] at 0.52 rad.s-1. The
percentage of type I fibres in the FAST group decreased from [53.8
(6.6)% to 39.1 (4.4)%] while type IIb fibre percentage increased from
[5.8 (1.9)% to 12.9 (3.3)%; P<0.05]. In contrast, the SLOW group did
not
experience significant changes in muscle fibre type or muscle torque.

We conclude that neuromuscular adaptations to eccentric training
stimuli
may be influenced by differences in the ability to cope with chronic
exposure to relatively fast and slow eccentric contraction velocities.
Possible mechanisms include greater cumulative damage to contractile
tissues or stress induced by slow eccentric muscle contractions.

============================
CHAPTER 8
"Testing and training for top Norwegian athletes" by P.E. Refsnes
page 97-115

There are indications,' however, that the fastest fibers are
preferentially recruited in the eccentric phase (Nardone et. al.
1989). The selective activation of the fastest fibers was however
most pronounced in fast eccentric actions.

===========================
Eccentric training takes place in most sports. Re training and safety it would depend on a number of factors including athlete qualification, goals, sport, bodyweight, programming and integration etc. But here are a few ideas:

*Weightlifting, skips, drop jumps.
*One could use a combination of weights + bands to enhance concentric
loading and eccentric acceleration.
*Drop and catch

Jay Schroeder seems to make use of various eccentric training methods.

Jamie Carruthers
Wakefield, UK
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