Pellegrino, J., & Dumke, C. L. (2013). The effect of plyometric training on running economy and titin. Medicine & Science in Sports & Exercise, 45(5), Supplement abstract number 739.

This study examined the effect of plyometric training on running economy and total titin and T1 and T2 titin isoforms [titin is a giant protein that functions as a molecular spring which is responsible for the passive elasticity of muscle.] Recreational runners (N = 20) completed a running-economy study involving a 6-week, 12-session plyometric-training routine. Ss were matched by age, gender, and various fitness parameters and randomly assigned to a plyometric treatment (N = 9) or control group (N = 11). Pre- and post-intervention outcomes included body composition, vertical jump, sit-and-reach, VO2max, onset of blood lactate accumulation, a 3-Km time-trial, running economy, and a vastus lateralis muscle biopsy for protein analysis.

Groups did not differ in any of the outcomes prior to the plyometric intervention. Plyometric intervention resulted in improved running performance but no improvement in running economy. The control group demonstrated improved flexibility and a decrease in vertical jump, while there were no changes in the plyometric group. No significant differences were found in titin or the two isoforms following plyometric training. Correlational analysis revealed a negative relationship for running economy at all speeds with flexibility (r = -0.46) and between running economy and titin, T1, T2, and the T1:T2 ratio at several running speeds. Titin, T1, and T2 correlated modestly and positively with vertical jump.

Implication. Plyometric training improved running performance despite no measurable change in running economy. Correlational analysis showed greater titin associated with greater oxygen consumption, which suggests that titin in the vastus lateralis does not act as a spring-like source of free energy during running. A more running-specific biopsy site (e.g., gastrocnemius) and a longer training intervention are suggested for future studies.

[Editor's note: Running economy is a measure of running-skill efficiency. Unless some training factor aims to change the mechanics of the skill, one should not expect any alteration in running economy from a physical training stimulus.

A further notable point of this study was the negative correlation between running economy and flexibility. Flexibility improvements are stressed in many training programs in a variety of sports without regard to affects on performance efficiency. Increasing flexibility might reduce the efficiency of function of specific muscles which will translate into lowered elasticity of muscles and decreased performance. Flexibility training should not be engaged in without careful consideration of its possible effects. It is well known that increased flexibility of the shoulders in swimmers increases the likelihood of shoulder injuries. There have been no studies relating increased shoulder flexibility with performance in swimmers. With sprint runners, increased leg and hip-joint flexibility has been shown to slow sprinting speeds.]

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