Isometric Training

Isometric exercises involve muscle contraction without a change in joint angle and any external muscle movement i.e., without lengthening or shortening the muscle (1). It is performed by holding a static position for a set period of time and can be performed without the need of complex equipment.     

In this mini article, we will discuss the benefits of isometric training, and whether it can replace dynamic strength training exercises.
 First, isometric training is often used in rehab settings. Studies have shown that it is suitable for people with injury or any medical condition that restricts movement (2), it also helped in relieving low back pain (3), knee pain (4), and neck pain (5). Moreover, isometric training can improve stability and the ability to hold weight over longer periods (6).
Second, Isometric training alone, was shown to be effective in increasing isometric muscular strength and hypertrophy (7,8) while requiring less energy demands than dynamic strength training (9,10). Especially during long isometric contractions (holding position for 30 seconds) which induced more strength and hypertrophy gains when compared to short isometric contraction (holding position for 3 seconds) (8). Nevertheless, it is important to note that even though isometric training can elicit increased muscular strength and hypertrophy adaptations without inducing the same level of fatigue compared to that of dynamic training, these adaptations are less pronounced compared to dynamic training. Hence, isometric training should not replace dynamic strength training (1).
Third, isometric training produces length specific adaptations (11). Which means, that the increase in strength and hypertrophy will be specific to the position in which the athlete is holding the contraction. Although this might be considered as a limitation, it can be turned to an advantage if programmed properly. In case, the athlete has a biomechanical disadvantage at a certain joint, adding some isometric exercises at that specific joint can help restore the length-tension relationship.
Fourth, although isometric training was previously associated with exaggerated hypertensive responses and contraindicated when training hypertensive individuals. Recent analyses suggested that isometric exercise might reduce BP in greater amplitudes than with cardiovascular and dynamic resistance training (12). However, due to the acute increase in BP as a response to exercise and possible complications, a medical clearance needs to be obtained prior to training and low to moderate intensities should be used to produce safe and minimal hemodynamic responses (13).
All the benefits mentioned above are related to the general programming, but what about their effect on dynamic sports performance? The studies in this regard are not 100% conclusive and most of them show better results when using dynamic strength training protocols. Still, as with general programming, performance was improved in some areas.
In sports requiring ballistic limb motions such as Muay Thai and MMA, isometric training led to greater improvements in impact force when compared to dynamic core exercises, on the other hand, dynamic strength training was superior in turns on strike velocity (14). Other studies that used multi-joint explosive isometric exercises showed improvement in both countermovement and horizontal jump performance (15). In cycling, isometric strength training led to a decrease in oxygen cost during moderate intensity exercise (16). Which means that the oxygen demands were less for the same bout. This decrease in oxygen cost was mainly attributed to muscle efficiency in extracting oxygen, hence, aerobic capabilities neuromuscular characteristics improved (16). As with other parameters, this improvement was also reported when using dynamic strength training protocols (17).
Takeaway Message
Isometric training can be added to the athlete’s program as a supplement to regular dynamic training since it helps in:
✓ Acquiring positive neuromuscular adaptations while inducing less fatigue.
✓ Improving strength at a joint that has biomechanical disadvantage. Especially when the length-tension relationship at the joint is altered.
✓ Improving some sports specific movements.
✓ Reducing both systolic and diastolic blood pressure in hypertensive individuals training at low to moderate intensities.


References
1.  Lum D, Barbosa TM. Brief Review: Effects of Isometric Strength Training on Strength and Dynamic Performance. Int J Sports Med. 2019 May;40(6):363–75. 
2.  Rosa UH, Velásquez Tlapanco J, Lara Maya C, Villarreal Ríos E, Martínez González L, Vargas Daza ER, et al. [Comparison of the effectiveness of isokinetic vs isometric therapeutic exercise in patients with osteoarthritis of knee]. Reumatol Clin. 2012 Feb;8(1):10–4. 
3.  Rhyu H-S, Park H-K, Park J-S, Park H-S. The effects of isometric exercise types on pain and muscle activity in patients with low back pain. J Exerc Rehabil. 2015 Aug;11(4):211–4. 
4.  Anwer S, Alghadir A. Effect of isometric quadriceps exercise on muscle strength, pain, and function in patients with knee osteoarthritis: a randomized controlled study. J Phys Ther Sci. 2014 May;26(5):745–8. 
5.  Khan M, Soomro RR, Ali SS. The effectiveness of isometric exercises as compared to general exercises in the management of chronic non-specific neck pain. Pak J Pharm Sci. 2014 Sep;27(5 Suppl):1719–22. 
6.  Lee BCY, McGill SM. Effect of long-term isometric training on core/torso stiffness. J Strength Cond Res. 2015 Jun;29(6):1515–26. 
7.  Schott J, McCully K, Rutherford OM. The role of metabolites in strength training. II. Short versus long isometric contractions. Eur J Appl Physiol. 1995;71(4):337–41. 
8.  Balshaw TG, Massey GJ, Maden-Wilkinson TM, Tillin NA, Folland JP. Training-specific functional, neural, and hypertrophic adaptations to explosive- vs. sustained-contraction strength training. J Appl Physiol (1985). 2016 Jun 1;120(11):1364–73. 
9.  Beltman JGM, van der Vliet MR, Sargeant AJ, de Haan A. Metabolic cost of lengthening, isometric and shortening contractions in maximally stimulated rat skeletal muscle. Acta Physiol Scand. 2004 Oct;182(2):179–87. 
10.  Newham DJ, Jones DA, Turner DL, McIntyre D. The metabolic costs of different types of contractile activity of the human adductor pollicis muscle. J Physiol. 1995 Nov 1;488 ( Pt 3):815–9. 
11.  Folland JP, Hawker K, Leach B, Little T, Jones DA. Strength training: isometric training at a range of joint angles versus dynamic training. J Sports Sci. 2005 Aug;23(8):817–24. 
12.  Carlson DJ, Dieberg G, Hess NC, Millar PJ, Smart NA. Isometric exercise training for blood pressure management: a systematic review and meta-analysis. Mayo Clin Proc. 2014 Mar;89(3):327–34. 
13.  Williams MA, Haskell WL, Ades PA, Amsterdam EA, Bittner V, Franklin BA, et al. Resistance exercise in individuals with and without cardiovascular disease: 2007 update: a scientific statement from the American Heart Association Council on Clinical Cardiology and Council on Nutrition, Physical Activity, and Metabolism. Circulation. 2007 Jul 31;116(5):572–84. 
14.  Lee B, McGill S. The effect of core training on distal limb performance during ballistic strike manoeuvres. J Sports Sci. 2017 Sep;35(18):1–13. 
15.  Tsoukos A, Bogdanis GC, Terzis G, Veligekas P. Acute Improvement of Vertical Jump Performance After Isometric Squats Depends on Knee Angle and Vertical Jumping Ability. J Strength Cond Res. 2016 Aug;30(8):2250–7. 
16.  Zoladz JA, Szkutnik Z, Majerczak J, Grandys M, Duda K, Grassi B. Isometric strength training lowers the O2 cost of cycling during moderate-intensity exercise. Eur J Appl Physiol. 2012 Dec;112(12):4151–61. 
17.  Støren O, Helgerud J, Støa EM, Hoff J. Maximal strength training improves running economy in distance runners. Med Sci Sports Exerc. 2008 Jun;40(6):1087–92.