Abstract:
The Active Isolated Stretching (AIS) technique proposes that by
contracting a muscle (agonist) the opposite muscle (antagonist) will relax through
reciprocal inhibition and lengthen without increasing muscle tension (Mattes,
2000). The clinical effectiveness of AIS has been reported but its mechanism of
action has not been investigated at the tissue level. Proposed mechanisms for
increased range of motion (ROM) include mechanical or neural changes, or an
increased stretch tolerance. The purpose of the study was to investigate changes
in mechanical properties, i.e. stiffness, of skeletal muscle in response to acute
and long-term AIS stretching for the hamstring muscle group.
Recreationally active university-aged students (female n=8, male n=2)
classified as having tight hamstrings, by a knee extension test, volunteered for
the study. All stretch procedures were performed on the right leg, with the left leg
serving as a control. Each subject was assessed twice: at an initial session and
after completing a 6-week AIS hamstring stretch training program. For both test
sessions active knee extension (ROM) to a position of "light irritation", passive
resisted torque and stiffness were determined before and after completion of the
AIS technique (2x10 reps). Data were collected using a Biodex System 3 Pro
(Biodex Medical Systems, NY, USA) isokinetic dynamometer. Surface
electromyography (EMG) was used to monitor vastus lateralis (VL) and
hamstring muscle activity during the stretching movements. Between test
sessions, 2x10 reps of the AIS bent knee hamstring stretch were performed daily
for 6-weeks.
