Gorgey, A. S., Mahoney, E. T., Kendall, T., & Dudley, G. A. (2006). Assuming recruitment of an entire muscle underestimates specific tension. Medicine and Science in Sports and Exercise, 38(5), Supplement abstract 721.

"Specific tension (ST) reflects the contributions of neural and musculoskeletal adaptations to loss or gain in strength. It is often assumed when expressing ST that the entire muscle can be recruited. This essentially negates neural factors contributing to performance. Although there are methods to quantify muscle size, none of them actually assess the amount of the muscle that was activated and involved during exercise".

This study attempted to express the specific tension of the quadriceps femoris group assuming the entire muscle is involved in a maximal voluntary effort vs. using magnetic resonance imaging (MRI) to measure the activated muscle during surface neuromuscular electrical stimulation induced isometric actions. Able-bodied Ss (N = 7) performed three trials of maximum voluntary isometric torque of the knee extensor muscle group. Ss also demonstrated their tolerance to electrical stimulation pulses and the amplitude set to evoke 75% of quadriceps femoris maximum voluntary isometric torque.

Results suggest that assuming the entire muscle mass is recruited during a maximal voluntary effort is incorrect and results in an underestimation of specific tension. When surface neuromuscular electrical stimulation is used to control recruitment at 100% of the stimulated muscle, specific tension is 20 % higher than when a maximal voluntary effort is made. Only 80% of the knee extensors are recruited during a maximal voluntary isometric effort. The positive relation between activated CSA and the resultant torque strongly suggests ST has meaning, but the correct factors must be used in its expression.

This study evaluated isometric contractions. When contractions are performed in movements (e.g., isotonic, isokinetic) recruitment would be even less. Thus, maximal movements are governed by patterns of specific recruitment of subsets of muscle fibers within the total muscle. Those patterns would need to be learned.

Implication. Maximal muscle contractions are governed by movement patterns and do not elicit total muscle involvement. [This study also points out why weight work does not benefit specific movements in high-level athletes. The patterns of weight exercises are not the same as the patterns of specific sport movements.]

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