Isometric Exercise hold times, are the length of the time you hold an isometric contraction for. The length of time one holds a given contraction varies greatly depending on who is giving the advice and it is by far one of the most confused, misquoted, poorly though out, mess of topic in regards to Isometric training in general. In this article I'll explain it all.
Briefly - you can adjust your Isometric exercise hold times and contraction intensity to produce different results within the body.
I use different isometric contractions, positions, times and intensity levels for different purposes, be it:
Each have their optimum path. ;-)
Different authors and physical culturists will recommend different times under isometric tension and this in turn affects your training frequency. Pete Sisco and John Little recommend as little as 5 seconds. Mueller and Hettinger recommend upwards of 10. Steve Justa advocates isometric holds for longer than three minutes, as does Matt Furey, and Shroeder. And Bruce Lee varied between 7 seconds and 8 hours. (Yes, he actually performed an 8 hour isometric hold - legend has it was a front shoulder hold).
The reason for this is intensity level and fibre stimulation. You can hold an isometric contraction with anything from 1% -100% intensity. Justa advised holds of 35% of max for long periods of time. (Similar to martial arts). Sisco and Little advocate a max contraction approx 90-100% for 5-7 seconds. I recommend a 7-12 second contraction because the majority of people starting these exercises cannot produce a full muscular contraction, even with the best of intentions and trying their hardest most will only produce an 80% contraction so a few additional seconds are recommended. Studies now show that as little as a 1/4 of a second in needed to stimulate growth and strength increases.
My second reason to recommend the 7-12 seconds is based on the energy pathways of the human body - our bodies were designed to exhaust Adenosine Triphosphate (ATP) stores in the muscle last for approximately 2 seconds and the re-synthesis of ATP from Creatine/Phosphate (CP) will continue until CP stores are depleted, approximately 4 to 5 seconds. This gives us around 5 to 7 seconds of ATP production. Repeat, 5-7 seconds. Thus, in order to stimulate your fast twitch fibres (those primarily associated with muscular size, strength and speed), anything after 7 seconds is unproductive.
However as I mentioned above, many students when starting CANNOT engage the maximal number of fibres straight off the bat and require upwards of 5 seconds to build to that contraction. Hence my recommendation. Some muscles however have a higher concentration of slow twitch fibres and intermediate fibres and thus require longer tension times to fatigue the muscle fully. You'll note in those exercises that the intensity of the exercise and the level at which you contract is reduced in consideration of the longer hold time.
In the next article I'll examine the individual fibre types and how they relate to different Isometric exercise hold times and different goals. ;-)