Quadriceps strength is important both in rehabilitation after knee injury, but also as a risk factor in developing knee osteoarthritis. Knee extension exercises are commonly prescribed to strength the quadriceps in knee patients; these exercises are commonly performed with various types of resistance, including isokinetic, isotonic, and elastic resistance.
Thera-Band® elastic resistance has been shown to produce similar muscle activation levels during upper body exercises when compared to isotonic dumbbells (Andersen et al. 2010). Recently, Aboodarda et al (2011) reported that an isotonic Nautilus machine produced similar quadriceps activation levels as Thera-Band-resisted knee extension; however, they only evaluated the quadriceps muscle.
Researchers in Denmark were interested in comparing the activation patterns and levels of multiple muscles during knee extension with a Technogym® isotonic machine and against Thera-Band elastic tubing. They tested 16 untrained adults using a 10RM resistance (the amount of resistance the subjects could move only 10 times). The 10RM level was determined a week prior to testing; the elastic 10RM was determined with a combination of different colors of Thera-Band tubing. Perceived exertion using the Borg scale was also measured during the exercises, which was found to be the same during both.
Surface electromyography (EMG) of 10 leg, abdominal, and lower back muscles was assessed. EMG was measured during both the concentric and eccentric phases of knee extension. They found no significant difference in maximal quadriceps activation levels between elastic and machine-based exercises during the concentric (knee extending) phase; however, they did find a significant difference during the eccentric (knee flexing) phase with significantly more rectus femoris and vastii activation with the machine-based exercise. This finding is not surprising as elastic resistance demonstrates the property of “hysteresis,” where the eccentric phase (returning from a stretched position) produces less resistance in the tubing.
As expected, both resistances exhibited similar “bell-shaped” activation patterns.
In addition, the researchers found a reciprocal relationship in the vasti muscles in the EMG-angle pattern between the 2 resistance exercises. The maximal activation of the vastii during the machine exercise occurred near the beginning of the exercise (near 70° knee flexion), while the maximal activation during the elastic tubing exercise occurred near the end of the range of motion (near 30° flexion). Interestingly, the vastus medialis to vastus lateralis (VM:VL) ratio never exceeded 1.0, and there was no difference between the types of resistance, “making both exercises optimal for maintaining patellar joint alignment,” according to the authors.
The authors suggested that the increased activation during elastic-resistance knee extension was due to greater elastic elongation near end range, stating:
“Accordingly, greater quadriceps muscle activity during extended knee positions, as observed using elastic resistance compared with machines, may be particularly beneficial for rehabilitation of knee pathologies such as ACL injury and following total knee arthroplasty where strength deficits have been observed to be present during the most extended knee angles.”
Interestingly, the elastic-resistance EMG pattern was similar to that described by Aboodarda in 2011: an increase in EMG toward the end of knee extension; however, they noted different EMG patterns between the Nautilus machine used in Aboodarda’s study and the Technogym knee extension machine used in their Danish study.
In conclusion, the authors stated,
“The knee extension exercise performed with elastic resistance seems to be a feasible and simple method, regardless of age and gender, for achieving high muscle activity potentially stimulating muscular hypertrophy and strength gains in the quadriceps muscles. Its portability makes it ideal for work site training, rehabilitation in hospitals, at home or in training fields where there may be few resources for large training equipment.”
REFERENCE: Jakobsen MD, et al. 2012. Muscle activity during knee extension strengthening exercise performed with elastic tubing and isotonic resistance. Int J Sports Phys Ther. 7(6):606-616