Chronic Flexibility Gains: Effect of Isometric Contraction Duration during Proprioceptive Neuromuscular Facilitation Stretching Techniques. (Physiology)
Rowlands, Ann V., Marginson, Vicky F., Lee, Jonathan, Research Quarterly for Exercise and Sport
The aim of this study was to assess the effect of two isometric contraction durations during proprioceptive neuromuscular facilitation stretching on gains inflexion at the hip. Forty-three women (M age = 20.0 years, SD = 1.3) were assigned to one of three groups: 5-s isometric contraction (5-IC), 10-IC, and control, Flexibility was assessed at baseline and Weeks 3 and 6. Analysis of covariance, controlling for pretest differences, showed a significant interaction, F(2, 33) = 44.1, p <.001. Flexibility was significantly lower in the control group relative to the 5-IC and 10-IC groups and in the 5-IC group relative to the 10-IC group at 3 and 6 weeks (3 weeks 101.2 [+ or -] 1.4[degrees], 114.3 [+ or -] 1.5[degrees], 120.5 [+ or -] 1.3[degrees]; 6 weeks = 103.0 [+ or -] 1.4[degrees], 126.1 [+ or -] 1.6[degrees], 133.3 [+ or -] 1.4[degrees] for control, 5-IC and 10-IC groups, respectively). A longer contraction time led to greater increases in flexibility.
Key words: flexion, hip, CRAC, PNF
Flexibility is defined as the range of motion (ROM) around a joint or group of joints (Alter, 1996) and reflects the ability of the muscle-tendon unit to elongate (Hubley-Kozey, 1991). Benefits of good flexibility include the reduction of injury risk and improved sport performance (Burke, Culligan, & Holt, 2000). Proprioceptive neuromuscular facilitation (PNF) stretching techniques have been consistently demonstrated as the most effective method for developing passive flexibility (Burke et al., 2000; Etnyre & Lee, 1988; Holt, Travis, & Okita, 1970; Sady, Wortman, & Blanke, 1982; Tanigawa, 1972).
PNF stretching techniques are based on optimizing relaxation of the muscles, facilitating a greater stretch. Contract-relax (CR) procedures lead to increased tension on the Golgi tendon organ (GTO) through the isometric contraction (Etnyre & Lee, 1987). This is thought to lead to autogenic inhibition, overcoming the myotatic reflex and reducing the neural activity in the stretched muscle. Contract-relax-agonist-contract (CRAG) procedures utilize additional reflexes in the form of reciprocal inhibition. The contraction of the agonist muscle group relaxes the antagonist muscle group, further decreasing neural activity in the muscle being stretched (Etnyre & Lee, 1987).
Etnyre and Abraham (1986) provided support for this theory by assessing the excitability of the motor neuron pool (indicated by the Hoffmann reflex response) of the soleus muscle during static stretching and PNF (both CR and CRAC techniques). All methods resulted in decreased excitability although the CR and CRAG methods resulted in greater decreases in excitability than static stretching. Furthermore, the CRAC method led to a greater and more sustained decrease in excitability than the CR method alone. The authors attributed this to an additive effect of autogenic and reciprocal inhibition (Etnyre & Abraham, 1986; Etnyre & Lee, 1987).
There appears to be a degree of uncertainty in the literature with regard to the optimal maximal voluntary isometric contraction duration during PNF stretching techniques. An isometric contraction of 6-10 s is commonly recommended (Allerheiligen, 1994; Anderson & Burke, 1991; McAtee, 1993; Preston, 1992). However, an isometric contraction duration of up to 20 s has been indicated (Norris, 1994). Clearly, there is a substantial difference between these recommendations.
The majority of the literature has used a 5-7-s isometric contraction (e.g. Etnyre & Abraham 1986; Hardy &Jones, 1986; Hartley-O'Brien, 1980; Holt et al., 1970; Lucas & Koslow, 1984; Sady et al, 1982; Tanigawa, 1972). With the exception of Hardy and Jones (1986), who had earlier observed a 6-s isometric contraction to be superior to 3s (Hardy, 1985), no justification for the use of these time spans was given.
There has been relatively little research into the optimal duration of the isometric contraction during PNF flexibility training. …