Strength Endurance for Kettlebell Sport, Part 2

Strength Endurance for Kettlebell Sport, Part 2

As mentioned in Part 1, kettlebell sport is associated with strength or power endurance.

Part 1 documented some approaches to building strength or power endurance in elite world champions. In part two, I will briefly examine what the science says about developing these qualities and highlight an effective and efficient way to develop this type of quality.

The scientific quality that most closely represents this is referred to as local muscular endurance. 

The main takeaway from the research is that if you increase your strength, you’ll increase the reps you can do with an absolute load.

A scientific study will typically assess one of three things:

1) absolute load such as 48 kg,

2) a repetition maximum (RM) % measured before the training intervention (%1RMPRE), 

3) a RM % measure at the end of a training intervention (%1RMPOST). 

In this blog, I will highlight a few interesting individual studies with slightly different methodologies. After that, I’ll look at some review papers that give you a bit more of an insight into what the whole Body of Evidence is saying about developing strength endurance. 

Here is an example of a study using a post-training RM%.

An important consideration in the above methodology is that if you increase someone’s strength with lower rep training, their post 1RM %  will be much higher than their 1RM %. 

For example, a study (1) comparing three training zones found:

• Low rep group (3-5RM x 4 sets)  improved leg press strength by 61%
• Intermediate rep group (9-11 RM x 3 sets)  improved by 32%
• High rep group (20-28 RM x 2 sets) improved by 6%

To test local muscular endurance they used a post-training 60% of 1RM. 

If they could all leg press 100 kg the group breakdown would be:

• Low rep group 161 kg
• Intermediate rep group 132 kg
• High rep group 106 kg

Not surprisingly the high rep group added more reps to their lower relative post 60% 1RM reps to failure, as they weren’t comparing like for like. 

The results were:

• Low rep group –20%
• Intermediate rep group + 10%
• High rep group + 94% 

One benefit of the high rep group side of training was that it did improve pure endurance performance without improving VO2 max—specifically the maximal power and time to exhaustion.

If you consider the last post of the very high rep (50-100 reps) ranges some of the benefits and improved performance may not be coming from improved strength endurance, but rather the training effect improving their pure endurance.

For GS high rep training could help improve endurance, but your time might be better spent doing more kettlebell sport sets as there will be better carryover. 

Alternatively doing traditional cardiovascular training might be a less stressful way to improve your VO2 max.

Here is a study using an absolute load to test strength endurance.

A study (2) using higher rep ranges compared rep ranges of 6-8, 30-40 and 100-150 in untrained men. The strength endurance was compared using an absolute load (~27 kg) reps to failure and found:

• rep ranges of 6-8, added 41% to total reps (~15 reps)
• rep ranges of 30-40, added 39% to total reps (~15 reps)
• rep ranges of 100-150, added 28% to total reps (~9 reps)

Again this shows that all the approaches are effective however you seem to get more bang for your buck with the lower reps (added max strength).

This study is interesting because it found different results in the upper and lower bodies.

Study (3) Contrast study two by using untrained women and testing both the squat and bench. The low rep range is the same as study 2,  while the medium rep range from study to is the large rep range in study three.

Squat improvements:

• rep ranges of 6-8, added  84%
• rep ranges of 15-20, added 80%, 
• rep ranges of 30-40 reps, added 137% 

Bench improvements:

• rep ranges of 6-8, added   58%, 
• rep ranges of 15-20, added 67%,
• rep ranges of 30-40 reps, added  54% 

In untrained women this would suggest that legs respond better to a higher rep range,  however this was not the case in the upper body. Suggesting that higher rep training may have better carryover in the lower body, but not the upper body.

What does the overall research say?

Three reviews have looked at the literature in its found similar results in favour of using heavy loading to improve absolute local muscular endurance (LME).

Here are some of their interesting points and conclusions:

Influence of total repetitions per set on local muscular endurance: A systematic review with meta-analysis and meta-regression

“The main finding of this review was that a higher compared to a lower number of repetitions per set was more effective for enhancing LME assessed via %1RMPOST. In particular, performing ≥ 15 repetitions per set compared to 7—13 repetitions was found to enhance

LME assessed via %1RMPOST. However, there were similar increases in LME following lower and higher repetitions when assessed via %1RMPRE.”

So this highlights that if you use the re-test RM value after a training block it will mask the improvement in endurance as your maximum strength has gone up. But if you use the pre-testing load you will see similar improvements in performance. So heavier training gives you a benefit in both strength and endurance, whilst lighter training seems to be endurance only.  

The strength-endurance continuum revisited: a critical commentary of the recommendation of different loading ranges for different muscular adaptations.

“When reviewing the data it appears that strength increases are not only attainable, but effectively the same, at both very heavy (maximal/near maximal) loads and more moderate loads of 8-12RM. Furthermore, that as strength increases so too does absolute- LME (local muscular endurance).”

“Effort and Discomfort 

When we consider heavier- and lighter-load RT, a factor that might become important when trying to exercise to momentary failure is that of discomfort compared to effort. There is a growing body of research supporting that discomfort (defined as the physiological and unpleasant sensations associated with exercise) is greater when performing exercise to momentary failure using a lighter- (50% MVC) compared to a heavier- (80% MVC) load in both males and females. This is potentially a result of increased blood lactate and cortisol accumulation and primarily thought to result from afferent feedback mechanisms. As such, it seems likely that the ability to reach momentary failure with lighter loads could be impaired by the discomfort during resistance exercise.”

This would imply that you’re lighter load training is improving your ability to tolerate discomfort, breaking psychological down barriers with the higher load training, rather than a true improvement in local muscular endurance. For the majority of people this can be accomplished with kettlebell sport training itself, so if recovery or time is a constraint then adding kettlebell sport sets or lower reps may be a better option.  

This could also explain why the time to exhaustion and aerobic power improved in the higher rep groups in the first study I looked at.

Loading Recommendations for Muscle Strength, Hypertrophy, and Local Endurance: A Re-Examination of the Repetition Continuum

Note on testing

“Although there is no generally accepted submaximal percentage for relative muscular endurance testing, it most commonly is assessed using loads between 40% and 60% 1RM” 

“Conclusions 

Despite the widespread acceptance of the repetition continuum as a loading paradigm, current research fails to support some of its underlying presumptions. The following evidence-based conclusions can be drawn when taking the body of literature into account, bringing about a new loading paradigm for exercise prescription.”

This takes aim at the traditional thinking of:

• heavy loads (from 1 to 5 repetitions per set with 80% to 100% of 1-repetition maximum (1RM)) optimize strength increases. 
• moderate loads (from 8 to 12 repetitions per set with 60% to 80% of 1RM) optimizes Muscle mass gains. 
• high repetitions with light loads (15+ repetitions per set with loads below 60% of 1RM) optimize local muscular endurance improvements. 

Suggesting that this structure doesn’t necessarily apply.

Lastly, tendon strength and stiffness can be improved the most with heavy training. 

 Improving tendon strength and stiffness is a great way to increase your body’s ability to absorb and utilize elastic energy via the stretch-shortening cycle. Tendons can be strengthened with Plyometric exercise or with resistance training.  Heavier resistance training of greater than 70% (~15RM) of 1 RM has larger increases in tendon’s stiffness than lighter loads. 

In conclusion, you can improve your strength endurance with of wide variety of rep ranges. It may be beneficial to use heavier loads as you have the added benefit of improving strength.  Lastly improving performance with very high repetitions may be more as a result of fatigue resistance as opposed to improve strengthen endurance.

I would suggest focusing on low to medium rep ranges as they may offer more benefits and be less taxing for most individuals. High repetition ranges can be used but you should ensure that you can recover from them.

Two simple and practical ways to implement some training options could be to start with a set that you can perform 15 times, each week add a little bit of weight and reduce the reps by one.  In contrast you could perform a set of 6 repetitions, over time building up your repetitions till you hit 15 and then add load starting again at 6 repetitions.

In the next blog, I will talk about my only experience and look at the variety of different methods that I’ve tried as a coach and athlete.

Extra reading

Study 1)

Muscular adaptations in response to three different resistance-training

regimens: specificity of repetition maximum training zones

Study 2)

Effects of three resistance training programs on muscular strength and absolute and relative endurance.

Study 3)

Strength/endurance effects from three resistance training protocols with women.

Tendon research

Mechanical, Material and Morphological Adaptations of Healthy Lower Limb Tendons to Mechanical Loading: A Systematic Review and Meta-Analysis