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Wednesday, August 3, 2011

Increased Muscular Strength Endurance Related To Reduced Running Fatigue

Increased Muscular Strength Endurance Related To Reduced Running Fatigue
June 26, 2011 By Neil Leave a Comment

Sweat Science just posted and summarized a new study from the Journal of Strength and Conditioning Research regarding the relationship between muscular strength endurance and running economy.

The researchers set out to determine if better muscular strength endurance allows fatigued runners to use less oxygen (i.e. maintain better running economy) at a given running speed. According to Sweat Science:

To test it, they asked 10 well-trained runners to do two 30-minute runs at a moderate pace. In the middle of one of the runs, the runners had to speed up to VO2max pace for four minutes, then slow back down — enough to tire them out a bit without exhausting them. As expected, their running economy got worse after the four-minute surge by 3.0%. This is typical: as runners get tired, their running economy gets worse.

Here’s a bit more detail: The moderate pace at which they ran was set at 20% less than their VO2max. During one run, the runners maintained this pace the entire 30 minutes. The other run began at this pace, inserted the four minute surge at VO2max pace, then returned to the original pace. By the end of both runs, oxygen demands increased though the moderate pace did not change.

Increase in Oxygen Consumption With and Without Surge

Oxygen demand in the 30-minute steady state run increased by 1.1% by the end of the run whereas oxygen demand after the surge run increased by 3% (see Figure 3). Not surprisingly, the addition of a mid-run surge caused greater fatigue.

Next, the researchers tested the muscular strength endurance of subjects’ hip and knee flexors and extensors using 2 sets of 20 isokinetic repetitions for each joint. They used the results to look for a relationship between eccentric muscular strength endurance at the knee or hip and the rate of increased oxygen consumption (i.e. decreased economy and relative fatigue) measured in the post-surge run.

Indeed, researchers found that rate of change in oxygen consumption under fatigue was “strongly related” to eccentric muscular strength endurance of the knee flexors.* Put another way, greater eccentric muscular strength endurance was associated with less fatigue.

It is unclear exactly how eccentric muscular strength endurance of the knee relates to mechanisms of running fatigue especially since running and fatigue are influenced by complex mechanisms. While researchers mention that increased ground contact time and less effective braking by the legs may help partially explain these correlations, they did not examine or discuss them in depth. They did however conclude as follows (emphasis added):

The results of this study indicate that eccentric strength expression may have a potential regulatory role in determining running performance. Of note, eccentric muscular endurance of the [knee flexors] attenuates fatigue-induced increases in [running economy] in well-trained runners; represented by enhanced fatigue resistance during steady-state trials. On the basis of these findings, it appears that conditioning work, which focuses on augmenting eccentric muscular endurance of the legs may offer beneficial adaptations that promote fatigue resistance.

Our results suggest that coaches and athletes could effectively implement conditioning strategies that challenge eccentric muscle actions. These strategies include plyometrics, resistance training with an emphasis on eccentric portion of repetitions, down-hill running and over-speed training. The findings of this study suggest that any such investment in these methodologies would be a valuable addition to the training portfolio of the middle or long distance runner, because they would serve to enhance [running economy] and ultimately delay the early onset of fatigue mechanisms.

We’ve added the study to our Research Library under: Hayes PR, French DN, Thomas K., “The Effect of Muscular Endurance on Running Economy.” J Strength Cond Res. 2011 Jun 17.

* Eccentric contractions of the hamstrings and accompanying flexor muscles at the knee are most active during running just before and at the moment the foot makes contact with the ground. Eccentric knee flexion not only helps accelerate your leg backwards just before striking the ground (known as the late flight stage), but it limits your leg from straightening and helps minimize braking when your foot lands (known as the early support stage). For more re: the biomechanics through stages of running see here and here, both mirroring versions of Baechle T., Earle R. Essentials of Strength Training and Conditioning. National Strength and Conditioning Association. Pp 462-468. 2008.

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