Isokinetic training: steady does it for serious gains

More generally, because a muscle can’t apply an equal force through an entire range of movement of an exercise, when you use a fixed weight to complete a set of repetitions, what you’re effectively doing is choosing the correct weight for the weakest point in the movement, in order to enable you to complete a set of reps. At other, stronger positions, you’re not using the optimum resistance. Isokinetic training on the other hand enables a muscle to mobilize its maximum force generating capacity at all points through the range of movement, by providing what’s known as an ‘accommodating resistance’⁽⁵⁾. In plain English, an accommodating resistance means that any effort put in by the user immediate produces an equal and opposing force.

By coupling this to a mechanical device, the speed of the movement can be controlled while the user puts in maximal effort throughout the whole range of movement. Not only is there more total muscular involvement, controlling the speed of movement to match that required in an athlete’s sport means that the muscle recruitment patterns can be more closely matched to those required in functional or sporting movements, helping to generate greater specificity.

What the research says

The theory that isokinetic training could bring specific benefits to athletes’ training programs is extremely plausible, but what does that actual data say about how effective (or otherwise) it is? One of the earliest studies into this topic was carried out over 40 years ago and published in the American Journal of Sports Medicine⁽⁶⁾.

This study compared the effects of isokinetic and isotonic resistance training. The participants were into four groups:

• Isotonic variable-resistance training
• Low-speed isokinetic training(conducted at 5, 10, and 15 reps per minute)
• High-speed isokinetic training (conducted at 30, 40, and 50 rpm)
• Control group (who did no training)

The results showed that all groups apart from the control showed good gains in strength when tested isometrically, isotonically, and isokinetically. However, when the individuals were tested for actual motor (ie functional) performance, the high-speed isokinetic group demonstrated superior gains. The high-speed isokinetic group experienced a 5.38% gain in the vertical jump versus 3.87% for the slow isokinetic, and 1.57% for the isotonic variable resistance. The respective gains in the standing long jump were 9.14% versus 0.42% and 0.28%. Likewise, the respective gains for the 40-yeard sprint were 10.11% versus 1.12% and 1.35% (see figure 1). When discussing the findings, the authors concluded that the large high-speed isokinetic gains were likely to the specificity of the movements – ie this mode of training most closely replicated the kinds of movements required in dynamic sports.

Figure 1: performance gains in high & low speed isokinetic vs. isotonic training

Strength gains and injury

During the 90s and early 2000s, further studies comparing isokinetic training to conventional weight training were carried out, many of which produced conflicting results. A major problem was that most of these studies did not use equivalent total loadings in their design; a study showing isokinetic training is more effective than conventional weight training is of limited use if the total work done in the isokinetic trial is significantly greater than in the conventional trial. All this would confirm is that training harder/longer produces superior results!

What was needed was a study where the total workload performed was identical in isokinetic vs. conventional training trials (in order to confirm that it’s the isokinetic element of the training that is responsible for the additional benefits). A 2010 study by French scientists looking at quadriceps muscle activity and strength attempted to do exactly this⁽⁷⁾. Thirty participants were split into three groups:

• Isokinetic training
• Isotonic training (ie with conventional weight machines)
• Control (no training)

Both training groups trained their dominant lower leg for three sessions per week for eight weeks on a dynamometer machine. The conventional group exercised using a preset loading of 40% of the maximal force they could exert at 70 degrees (0 degrees = leg in horizontal position). This loading simulated a fixed weight loading just as in a leg extension machine. The isokinetic group exercised isokinetically at a velocity ranging between 150 degrees and 180 degrees per second. Importantly, the standardization of these two training programs was ensured by the equalization of the total external amount of work performed across the groups, and the overall movement speed.

The key finding was that after eight weeks of training, both groups experienced significant and comparable strength increases when tested in both dynamically and statically. In addition, there were no noticeable changes in muscle electrical activity between the two groups. These findings fit with those from a later (2017) study, which looked at six months of quadriceps strength building using isotonic vs. isokinetic machines following athletic injury⁽⁸⁾.

This study concluded that quadriceps strength developed on a weight machine was equally as good as that developed on an isokinetic machine. It also found that once retuned to sport, the athletes in both groups had equal functionality. The authors noted that their findings were significant because isokinetic dynamometer systems are relatively expensive and their operation requires more logistic effort and technical skills. In plain English, athletes undergoing rehab shouldn’t necessarily feel they’re missing out because they don’t have access to isokinetic training machines!

Analyzing movement patterns and injury rehab

Most dedicated isokinetic resistance machines generate resistance electronically. By adding motion and force sensors and a computer interface, athletes can use them both to build strength and power, and to analyse movement and ‘force curve’ patterns, which can be very useful for athletes or sportsmen and women. For example, suppose a runner with a history of knee injuries wanted to investigate how efficiently their frontal thigh muscles (quadriceps) were working. By performing a set of reps on an isokinetic machine, he or she could draw up a force-power curve, displaying exactly how much force the muscles were producing at every single point throughout the range of movement.

This can be very useful in injury rehab, where muscles may need to be worked through a particular range of movement to rehabilitate an injury, protect against re-injury or (in conjunction with other muscle groups) to help produce a more biomechanically balanced pattern of movement to protect against chronic overuse injuries. This kind of analysis is also extremely valuable in sports performance. Front crawl swimmers for example need a long stroke through the water and must be able to push hard, even right at the end of the stroke before the hand leaves the water. Force-power curves from an isokinetic machine can analyse how effective the lats of the back and the triceps of the upper arm are at producing force through that range of movement.

Isokinetic training and functional performance

At this point, athletes and their coaches might be feeling less than convinced about the merits of isokinetic training. In more recent years however, newer data has emerged showing that when it comes to function sports-specific strength, isokinetic training may offer some distinct advantages. In a Brazilian study published four years ago, researchers compared muscle strength, muscle mass, and functional performance in response to isometric, isotonic, and isokinetic contractions - importantly, when training loads (volume and intensity) were equalized across all the modes of training⁽⁹⁾.

Thirty one men were assigned to isotonic (IT), isometric (IM), or isokinetic (IK) groups, and trained their dominant quadriceps muscle three sessions per week for eight weeks with a dynamometer. Muscle strength was assessed using Cybex 6000 dynamometer, while the triple-hop-distance test was used to assess functional performance. Also, the highly accurate technique known as dual energy X-ray absorptiometry (DEXA) was used to assess lean muscle mass changes.

After eight weeks of training, muscle lean muscle mass increased by 3.1% in the isometric group and 3.9% in the isotonic group. Meanwhile, the mass gains in the isokinetic group were only small and non significant. BUT, when it came to functional performance, only the isokinetic group showed a significant improvement in the triple-hop-distance test (by 4.84%) whereas both other groups saw no increase in functional performance.

Functional performance gains with isokinetic training may also be specially relevant for athletes such as swimmers, rowers and kayakers, where the movement of the hand/paddle through the water has a similar force/time curve to that produced with an isokinetic resistance training machine⁽¹⁰⁾. According the specificity of training principle, training for strength in a manners that most closely mirrors the biomechanical demands of the sport is likely to produce the best results⁽¹¹⁾.

In a study on elite canoeists, researchers examined the effects of eight weeks of isokinetic training of the trunk muscles and how it functionally affected the ability of the athletes to exert force in the water with a paddle⁽¹²⁾. The results showed that isokinetic trunk rotator training was effective in improving concentric trunk rotator strength in world-class canoe sprinters, and also that the improved trunk strength led directly to improved paddling forces in the water. This is in contrast to a large number of previous studies that found trunk strength development using conventional isotonic training modes did NOT improve in-water performance in canoeists and kayakers⁽¹³⁾.

Advice for athletes

Let’s try and bring these findings together to reach some conclusions. Isokinetic training for strength offers theoretical benefits, but not in all circumstances. When it comes to out and out strength and muscle mass, there’s no robust evidence that it is superior to conventional resistance training with weights. Indeed, training with a fixed weight resistance may actually produce better results. And while it is more controllable in a physio’s clinic, there’s no particular reason to assume that isokinetic strength training leads to better rehabilitation outcomes than other resistance methods.

Where it may offer a distinct advantage is in functional performance, especially in sports that involve hydrostatic resistance (canoeing, swimming etc) and where force needs to be developed rapidly through a large range of motion. In these circumstances, the ability to mimic muscle movement patterns on an isokinetic machine offers greater training specificity, which may therefore result in greater functional performance (the bottom line!).Therefore, if your gym or training facility has some isokinetic resistance equipment, count yourself lucky because you could do far worse than to supplement some of your normal weight training with some isokinetic work – particularly by training the key muscles in your sports through a similar range of movement and at reasonably fast movement speeds (up to around 150 degrees per second).

The challenge for most athletes is getting access to isokinetic machines. However, if that’s the case, all is not lost because some electronic cardiovascular machines actually offer an isokinetic-type training option. For example if a stationary bike has a constant ‘RPM’ setting, you can use it for isokinetic work. Simply punch in the cadence at which you want to pedal and the bike’s electronics will ensure a constant speed of movement. By selecting a relatively slow rpm and putting in some big efforts, you can create an isokinetic resistance training effect! You can also do something similar with some air-braked machines such as Concept II’s rower. Unless you’re particularly strong, by fully opening the cage and admitting as much air as possible, you’ll probably find that once your rowing cadence gets beyond a certain speed (quite slow), the air resistance will exert an almost isokinetic effect. Putting in some big efforts will simulate isokinetic resistance training for the rowing muscles. Likewise, runners may be able to benefit from some elliptical training machines that offer fixed rpm training (as described for cycling). The key thing to remember however is that ALL forms of strength training can offer big benefits to athletic performance, so if topping up your normal resistance training with isokinetic work is difficult, don’t worry – you’ll still make great gains with weights!

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