Danny is Head of Strength & Conditioning at the Singapore Sports Institute for seven years,and also currently doing a PhD with a research focus on Isometric Strength Training for Sports Performance. Prior to that he was the Strength & Conditioning Officer for the Singapore Armed Forces so was dealing with Military Training.
Danny completed his undergraduate degree at the University of Western Australia (UWA) prior to doing the role in the Military for two years.
What options have we got when it comes to Isometric testing?
”There are single joint testing options as well mainly using the biodex equipment for rotator cuff internal/external rotation of shoulder, knee flexion/extension. We also have multi-joint isometric testing such as isometric squat, isometric mid-thigh pul (IMTP), isometric bench press and isometric prone bench pull.”
Why would we go down that route in the first place with Isometric testing vs. something more dynamic?
”The information we can get from isometric testing includes not just the peak force, but also the rate of force development (RFD) and if we combine the data we get from the counter movement jump (CMJ), and IMTP for example, we can actually calculate the dynamic strength index, which I believe many coaches are using it as an indication of whether they should train their athlete more with plyometrics or with heavy strength training.
Some of the advantages of isometric training is that it is much safer because there is no movement involved you don’t get injured that easily, and it’s pretty quick, 5-seconds and you’re done. The disadvantage is you can’t really use it for exercise prescription, like a 1-RM strength test.
Quite a lot of studies have shown the peak force and the RFD are significantly correlated to activities like sprinting, jumping and change of direction. There are also studies that have looked at striking, throwing and recently we did a study with sprint Kayaking. I want to think that isometric strength assessment data will have a high correlation with activities that has mainly concentric contractions like cycling and sprint Kayaking, but the relationship with dynamic activity that requires the stretch-shortening cycle with the eccentric and concentric phase might not be as great.
If you look at the literature and take IMTP and isometric squat for example, the relationship you get from the peak force with CMJ range from R = 0.30-0.80 so the range is pretty huge. There could be a lot of reasons for this; it could be because of the familiarization, different athletes with different training experience and different strength levels and also the time of the year and the training phase they are in.
Another thing to look at is the joint position where the test is conducted. So for example, if you look at the literature you will see that the isometric squat when tested at a 90 degree knee angle vs. 120 degree knee angle; the relationship between the isometric peak force obtained and CMJ jump height will be higher when the peak force was obtained at a 90 degree knee angle, and same for sprint performance. What we can get from this, is that if you want to conduct the isometric strength test to see if there is any relationship with a certain activity, probably get the person to adopt a joint position whereby the concentric force is initiated at 90 degrees. This makes sense because the CMJ is usually initiated from a position where the knee is at an angle of about 90 degrees.
But there is something interesting- that works for squat, but IMTP doesn’t work that way! You can see that a IMTP is usually conducted at a knee angle of around 130-140 degrees, yet the magnitude of the correlation with the CMJ height is as high as that obtained for the isometric squat at 90 degrees! This is something I personally do not understand!!”
What is the dynamic strength index and why would coaches be interested in it/calculate it?
”First we collect the peak force from IMTP- theoretically that is the highest amount of force your lower limb can produce. You can also obtain the peak force of the CMJ. Then you can divide the peak force of the CMJ by the peak force of the IMTP
Dynamic Strength Index = Peak Force IMTP / Peak Force CMJ
The isometric peak force on an IMTP is the maximum amount of force you can produce and how much of this force can you translate into a dynamic movement. The Dynamic strength index provides you with an indication, so I think if it is below 0.65 this indicates that your athlete might need a little more ballistic training like plyometrics. But if the dynamic strength index is above 0.80 then the athlete probably needs more heavy strength training.”
Isometric training as a training tool- what benefits are people going to get from isometric training?
The disadvantage is that people believe that with isometric training you only gain strength in that specific joint angle that you train at, of course when you look at the literature, this is not true.
The adaptations from strength training are similar to dynamic strength training. You still get increased neural firing, neural recruitment and hypertrophy of muscle. One of the adaptations from isometric training that is superior to dynamic strength training is the increase in tendon stiffness.
This has high implications on RFD, so with greater tendon stiffness the force transmission from the muscle can be more efficient and will improve force production and RFD.”
When creating isometric exercises in some very sport specific positions what kind of creative process are you going through when thinking about integrating some of that into these sports?
I just completed one study with recreational runners where we compared plyometric and isometric training for endurance running performance. For the isometric training they did a IMTP and an isometric plantar flexed ankle, so the ankle was in a neutral position when they did the plantar flexion. What we found was that running economy was actually improved with the isometric group as compared to the plyometric group. One possible reason is because recreational runners tend to avoid heavy strength training so with the isometric exercises as a stimulus that greatly improved their strength. In that sense, people might ask if that would work with elite runners, and that would need to be researched.”
When it comes to programming isometrics within the wider programme (annual plan) where does it fit?
At different joint positions you might induce hypertrophy at different parts of the muscle.
Top 5 Take Away Points:
- Isometric is a safe and effective way of performing strength testing and training.
- Dynamic strength index = Peak Force IMTP / Peak Force CMJ
- Importance of range of motion- strength gains will increase across a greater range of motion as compared to a quadriceps at a short length.
- Importance of tendon stiffness- one of the adaptations from isometric training that is superior to dynamic strength training is the increase in tendon stiffness.
- Considerations when choosing position- the place where the concentric action is initiated, and the position which reflects the bio-mechanically most disadvantageous position.
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