Exercise-Based Interventions

 

 

Progression of the estimated eccentric work volume produced during the 12-week intervention period

 

Hernandez HJ, McIntosh V, Leland A, Harris-Love MO, 2015  (doi:10.3389/fmed.2015.00045)

 

Our lab group is currently conducting a RCT involving progressive reseistance exercise with eccentric loading in Veterans with knee arthritis. The 3-D surface plot depicts the estimated unilateral eccentric (Ecc) work produced by the less involved limb (right side) knee extensors over the course of the exercise regimen. The work produced is a function of the isokinetic torque produced during knee excursion and the exercise volume (in repetitions and sets). Thex-axis features exercise sessions (two per week, for a total of 24 sessions), the y-axis includes the agonist muscle groups (knee flexors and extensors), and the z-axis includes the estimated work yield per exercise session (ft-lbs).

 

Note that the lower work volume at the start of the regimen (the dark blue region on the right side of the plot) corresponds to the lower torque targets that characterize the “Familiarization” and “Acclimatization” phases of the eccentric exercise regimen, and may have afforded a protective adaptation against excessive muscle damage during the subsequent exercise bouts marked by higher work volumes and torque levels during the final 4 weeks of the “Progression” phase (the red region on the left side of the plot).

Pre and post-intervention ultrasound images of the rectus femoris following the 12-week intervention period

 

Hernandez HJ, McIntosh V, Leland A, Harris-Love MO, 2015  (doi:10.3389/fmed.2015.00045) 

 

The longitudinal B-mode ultrasound images of the less involved limb (right side) were obtained with a 13–6 MHz linear array transducer and using the averaged digital caliper values from three measurements. The rectus femoris of the less involved limb had an increase in muscle thickness from 3.97 to 4.32 cm, whereas the more involved limb experienced a change in muscle thickness of <0.1 cm.

 

These physiologic adaptations to an eccentric training stimulus were consistent with our observation of the patient’s post-exercise changes in morphology and morphometry of the rectus femoris. Increases in rectus femoris muscle thickness, which are indicative of muscle hypertrophy, and possible improvements in muscle quality based on the lower ­echointensity values were noted in the patient’s Week 12 measures and are consistent with previously reported findings in healthy younger adults.

 

Additional investigaton will be needed to better understand the patient response to eccentric PRE based on estimates of OA severity and levels of patient disability. 

The "Power-Velocity Paradox": eccentric exercise power production differs greatly from concentric exercise at higher movement velocities 

 

Harris-Love MO, Seamon BA, Gonzales TI, Hernandez HJ, Pennington D and Hoover BM, 2017  (doi: 10.3389/fphys.2017.00112) 

 

The power-velocity relationship for eccentric muscle actions differs greatly in comparison with concentric muscle actions as shown in the idealized graph depicted in the figure. Peak concentric power is attained at intermediate velocities and peak torque levels, whereas, peak eccentric power rises precipitously with increasing velocities and fairly stable high peak torque levels.

The participants (n=24) in our study used the same workload targets during exercise at two isokinetic speeds: 60° s−1 and 90° s−1. The data attained during the 90° s−1 condition show that the attained peak torque values were comparable to those recorded during the 60° s−1 condition (Δ 7%). However, a greater proportional difference in mean power generation was noted in the 90° s−1 condition in comparison to the 60° s−1 condition (Δ 25%) within the sample.

Unlike concentric muscle actions, increased movement velocity during eccentric muscle actions may significantly affect exercise intensity even when program variables such as workload and repetitions remain unchanged. Practitioners should be aware that peak eccentric muscle torque or force may remain high during activities designed to maximize the production of peak eccentric power.

 

(The indeterminate physiologic decline in power at the highest velocities is denoted by the terminal bar on the dashed trajectory line; con, concentric; max, maximum)