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  • Interference in task learning/specificity of training

    Dear members,

    Several weeks ago I asked for information regarding task performance after
    learning either in isolation or concurrently with other tasks. I had
    performed a resistance training study where subjects also performed sprint
    running and vertical jump training concurrently. I found no differences
    between my groups in either the running/jumping or resistance tasks after a
    short period of training. This is despite other studies using only one
    form of training reporting significant training-specific adaptations to
    resistance training. Now that I have had time to review the literature I
    am able to provide a detailed summary. A brief account of my study is
    presented below, it may be easier to read the following if you have
    reminded yourself of the study. Any discussion or feedback is welcome.


    First, it is important to discriminate between two theories of learning.
    The first is the specificity of learning principle that states that
    performance in a task is better when the training for that task is more
    specific or similar. Second is the contextual interference theory that
    proposes that learning is enhanced when practice similar, but not
    identical, tasks are presented in a random order. From the studies I was
    able to find, I noticed that research into the specificity of learning
    principle used a methodology where several practice tasks were used in
    isolation by different groups. Those who trained with a task very similar
    to the test task had the best improvements in performance. However,
    research into contextual interference used methodologies where several
    tasks were performed concurrently in training. Results suggest that task
    learning is enhanced when several different tasks are performed in a random
    order than when one task is performed in isolation in training. This
    second methodology most closely resembles the methodology used in my
    training study. In my study, I had three groups, two of which performed
    resistance training and sprint/jump training (although they used different
    resistance training exercises) and one that performed only sprint/jump
    training. Using the theories of contextual interference, the groups should
    have been able to perform all the tests simlarly (including the resistance
    exercises since they were chosen to be similar to either the jump or sprint
    movements) since all the groups trained using several different tasks.
    Their ability to perform at any task that is similar should then have been
    improved. It is important to note that the short period of 'specific'
    training (5 weeks, they also performed 4 weeks of non-specific training
    first) was not sufficient to stimulate gains in muscle size, therefore any
    adaptation should have been largely neural, or due to learning. If the
    contextual interference between the groups was simliar, then all groups
    should have improved the same.

    A second piece of information that was important in explaining the outcome
    of my research was provided by Daniel Ferris. He emailed me two abstracts.
    The first was by Brashers-Krug et al. (see below for reference). The
    authors found that the learning of a second motor task was not disrupted if
    learned 4 hours after another since the delay allowed for consolidation.
    Also, Norrie and Henry (see below for reference) found that if a novel task
    was performed during rest periods in the learning of a task, performance in
    the learned task was significantly reduced. This is possibly because
    consolidation did not occur during rest. In my study, the sprint/jump and
    resistance sessions were performed on different days, therefore there was
    equal consolidation between the groups. The group that performed no
    resistance training performed sprint and jump training only, but both in
    the same session. One might have predicted that since this group performed
    twice the number of sprint/jump training sessions, they might have improved
    more in a short period of time that the resistance groups (expecially since
    only small strength improvements in the resistance groups might have been
    possible). However, the interference caused by practicing two tasks in
    succession with no period of consolidation could have hampered the task
    improvements in this group.

    A third piece of important information was from a PhD dissertation
    performed by Daniel Ferris (dferris@ucla.edu). He found that performance
    in a circle-forming motor task was simliar between groups who practiced
    with an easy, complcated or several combined methods of drawing the
    circles. He concluded that learning occurs at a perceptual rather than
    specific level regardless of the details of the practice. This suggests
    that in my study, there should be no difference between the resistance
    training groups. While the movement patterns of the two exercises
    differed, the subjects were able to use the lessons learned in practice for
    one task to improve their performance in another. Unfortunately I could
    not find any similar research in the SportDiscus or PsychLit databases. I
    therefore could not determine why tasks seemed to be learned at a
    'perceptual level' when a large body of research suggests that adaptations
    to task training can be very specific.

    However, it is now possible to speculate as to why I did not find any
    difference among my training groups. First it is important to note that
    performing concurrent strength and sprint/jump training is very different
    from performing such discrete tasks as those used in many motor control
    studies. Nonetheless, the theories from motor learning seem to be able to
    explain why I found no between-group differences in my study when other
    studies that only examined the influence on training of one specific task
    showed that the adaptations to that task were very specific. First, all
    groups had contextual interference in their training allowing for a similar
    improvement in performance between the groups. Second, it was likely that
    a similar performance improvement would occur between the resistance groups
    because the task and resistance sessions were performed on different days.
    This allowed for consolidation. The group that performed twice as many
    sprint/jump sessions did not improve more than the resistance groups (which
    could be likely given no muscle size increases and thus little actual
    muscle force increases were likely, and the resistance groups only
    performed two sprint/jump sessions per week) possibly because the
    sprint/jump sessions were performed with no rest between the training of
    the two tasks. This would have limited the consilidation of each task and
    limited improvements. Third, it is possible that learning of complex tasks
    occurs at a more perceptual level than previously thought. Therefore
    subjects were able to use 'techniques' learned on one task to successfully
    improve other similar tasks. This minimised any differences between the
    groups.

    Of course it is also important to mention that the subjects were all good
    athletes from a back ground generally of soccer, rugby, rugby league or
    netball and all subjects performed 4 weeks of supervised resistance and
    sprint/jump training prior to the 5-week specific training phase.
    Therefore, the sprint and jump techniques of all subjects would have been
    good and unlikely to change significantly in the following 5 weeks of
    training. As far as the resistance training is concerned however, research
    into movement-pattern specficity of training suggests that even well
    trained strength athletes improve rapidly when training at a novel strength
    task. Thus I might have expected differences in strength performance
    between my resistance groups where each group improved most at the exercise
    they used in training. The fact that there were no differences between my
    resistance groups might be explained by the three reasons described above.

    Authors mentioned in responses:

    Shea & Kohl (especially 1990's)
    Shea & Wright (especially 1990's)
    Susan Higgins
    Claude Ghez
    Jim Gordon
    Timothy Lee
    Guadagmoli, M
    Reza Shadmehr (John Hopkins University)
    Franklin Henry
    Gentile, AM (Medicine and Science in Sports, 1992)
    Magill & Hall (Human Movement Science, 1990)

    Noted references:

    Brashers-Krug T, Shadmehr R, Bizzi E. Consolidation in motor memory. Nature
    July: 18, 382(6588): 252-255, 1996.

    Norrie ML, Henry FM. Influence of an interpolated non-related motor task on
    shrot- and long-term memory learning and retention of a gross motor skill.
    Perceptual and motor skills June: 46(3 Pt 1): 987-994, 1978.


    Overview of training study and results:

    Adaptations to resistance training are specific to the velocity and
    movement pattern of the training exercises. For example, if someone trains
    with a particular exercise (eg a cable tricep extension) the strength
    gained does not transfer well to other, similar, exercises (eg an overhead
    tricep extension). Furthermore, these 'specific' strength adaptations can
    occur over a short period of time (many studies have shown joint
    angle-specific adaptations to training after training periods of only 4-6
    weeks [Kitai & Sale, 1989; Thepaut-Mathieu et al., 1988; Weir et al., 1994,
    1995]). Thus many athletes try to mimic their sporting movements when
    performing resistance training. However it has not been shown
    experimentally whether 'specific' resistance training is associated with
    greater improvements in a sporting task than 'non-specific' resistance
    training when both resistance and task training are performed concurrently.
    I therefore conducted a 5-week (+ 4-week 'non-specific' lead-in training)
    training study to examine short-term changes in sprint and vertical jump
    performance after a period of concurrent task and resistance training.
    Briefly, three groups performed sprint and vertical jump training with one
    of these groups performing moderate to high speed squat lift training and
    one of these groups performing a new exercise (coined the 'forward hack
    squat': a unilateral squat-like movement performed with the body prone to
    45 deg and the hip and knee angles moving through very similar ranges of
    motion to those in the acceleration phase (0 - 20 m) of running) in
    addition to their running training. Despite fully supervised training and
    a high training attendance by subjects we found no difference between the
    groups in neither sprint or jump performance, nor in their performance in
    the resistance exercises.

    Given that the movement patterns of the resistance exercises were so
    different, I expected large inter-group differences even if there were no
    differences in sprint/vertical jump performance between the groups.
    Isokinetic testing showed changes in the angles at which the groups
    produced maximum torque in an isokinetic knee extension such that the squat
    group acheived their maximum at a more closed angle after training while
    the forward hack squat group acheived their maximum at a more open angle.
    This difference however only approached significance (p=0.054).
    Nonetheless it suggests that some adaptations may have occurred and that
    these adaptations differed between the groups. It is my theory that
    perhaps performing sprint/jump training concurrently with resistance
    training interfered with the learning of the resistance tasks. I would
    assume that if the groups only performed weight training we would have seen
    differences between the groups in resistance exercies performance. Perhaps
    if the training period had been longer we might still have seen
    training-specific adaptations, but these adaptations might have occurred
    slower during concurrent resistance and sprint/jump training than when only
    resistance training is being performed. I therefore would like to access
    literature examining the time-course of learning when tasks are practiced
    in isolation and concurrently with other tasks. I am using the term
    learning because I assume that any change in performance within the first
    few weeks would be due to changes within the nervous system affecting
    muscle recruitment patterns etc., i.e learning.

    Thanks for your help.

    Tony.



    ************************************************** ****************
    Anthony (Tony) Blazevich
    School of Exercise Science and Sport Management
    Southern Cross University
    Lismore NSW Australia, 2480

    Email: ablaze20@scu.edu.au
    Phone: +61 2 6620 3231
    Fax: +61 2 6620 3880
    Mobile: 0416 200 674 (Australia only)

    ************************************************** ****************

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