September 2021

Plantar Flexor Activation in Multi- and Single-Joint Resistance Exercises

By Paulo Gentil, Daniel Souza, Murillo Santana, Rafael Ribeiro Alves, Mário Hebling Campos, Ronei Pinto, and Martim Bottaro

These authors hypothesize that calf raises would elicit superior activation of soleus, lateral, and medial gastrocnemius muscles in comparison to leg press.

Resistance training (RT) is a popular mode of physical exercise often associated with voluntary muscle contraction against an external load, and its regular practice has been advised as an essential part of physical conditioning programs. RT benefits are often associated with improvements in the musculoskeletal system such as increased muscle strength and hypertrophy, improved bone health, reduced low-back pain, and better functionality. Such adaptations are influenced to some extent by the mechanical stimuli provided by repeated muscle activation in a process called mechanotransduction. Muscle activation and subsequently mechanical stimuli might be affected by the manipulation and combination of RT variables such as load, rest between sets, and exercise selection.

Regarding exercise selection, RT can be performed with single- (SJ) or multi-joint (MJ) exercises, depending on the number of joints involved. For upper body muscles, it has been well established that SJ and MJ exercises promote similar levels of muscle activation, as well as similar increases in muscle size and strength. Moreover, other studies showed that, in general, the addition of SJ exercises to an RT program involving MJ exercises might not be necessary to bring optimal results in terms of muscle size and strength. This brought the suggestion that one can chose between SJ and MJ exercises based on personal preferences and practical aspects, without any negative impact on the results obtained from the intervention. Although less evidence is available for the lower body, studies about muscle activation, muscle strength, and hypertrophy showed the same trends for thighs and hip muscles. However, information for calf muscles is scarce and controversial.

Bryanton et al reported near maximum efforts of the plantar flexors during the squat, when compared to the torque produced during a maximum isometric contraction. Interestingly, the relative muscle effort of the plantar flexors during the squat was similar to the ones of the hip and knee extensors, suggesting that the plantar flexors have an important involvement in the exercise performance. On the other hand, Escamilla et al reported that the activation of the plantar flexors was relatively low during different variations of the squat and leg press (9–17%), when normalized to a maximal isometric contraction. In addition to the controversial findings, these previous studies only analyzed MJ exercises and did not compare MJ and SJ under similar load conditions. Therefore, the current literature does not allow to conclude if plantar flexor muscle activation during a MJ exercise would be equivalent to the activation obtained during SJ exercises.

Some studies suggested that activation might be important for muscle adaptations, since mechanotransduction is likely to occur only in muscle fibers activated during exercise. This suggests that high levels of muscle activation produced from repeated contractions can provide stimulation to the muscle, especially when combined with other factors, such as mechanical and metabolic stress, muscle swelling, etc. Therefore, considering that electromyographic (EMG) activity may reflect greater challenges to the musculoskeletal system, the investigation of plantar flexors muscle activity during MJ and SJ exercises using EMG analysis might contribute to close the gap regarding this topic.

Although plantar flexors are not commonly studied, their morphology and function might be important in clinical conditions such as chronic venous insufficiency and venous leg ulcers. Moreover, strengthening the plantar flexors might have important applications in rehabilitation, to maintain orthostatic tolerance during exposure to microgravity, improve balance, decrease the risk of falls, treat Achilles tendinopathy, and improve functionality.

Therefore, knowledge about how different exercises recruit these muscles might be of clinical and practical relevance. Based on the lack of information about plantar flexors’ activity during SJ and MJ exercises and the clinical and practical importance of the plantar flexors, the purpose of the present study was to compare soleus, lateral, and medial gastrocnemius muscles activation during leg press and calf raises in trained men. Our hypothesis is that calf raises would elicit superior activation of all muscles analyzed in comparison to leg press.

The study involved 22 trained men (27.1 ± 3.6 years, 82.7 ± 6.6 kg, 177.5 ± 5.2 cm, 3.6 ± 1.4 experience years) who performed one set of each exercise using a 10-repetition maximum (10RM) load in a counterbalanced randomized order and separated by 10 minutes of rest. The EMG signal was measured for the 3 major plantar flexors: soleus, medial, and lateral gastrocnemius.

Figure 1. Illustration of exercise testing procedure (A), and electrode position during leg press (B) and calf raise (C).

Results

Comparison between groups showed that mean EMG values during the leg press were 49.2% for the lateral gastrocnemius, 51.31% for the medial gastrocnemius, and 50.76% for the soleus. Values for calf raises were 50.7%, 52.19%, and 51.34% for the lateral, medial gastrocnemius, and soleus, respectively. There were no differences between exercises between groups for any muscle and the Effect Size (ES) of differences were trivial (gastrocnemius lateralis (P = 0.230, ES = 0.18), gastrocnemius medialis (P = 0.668, ES = 0.08), and soleus (P = 0.535, ES = 0.07).

There is a significant correlation between the leg press and calf raise mean EMG for the lateral gastrocnemius (P = 0.04) and the soleus (P = 0.02), but not for the medialis gastrocnemius (P = 0.41). The Bland-Altman plot showed systematic bias of -1.5 ± 5.7, -0.9 ± 9.5 and -0.6 ± 4.3 for the lateral gastrocnemius, medial gastrocnemius, and soleus, respectively. The presence of proportional bias was verified for the medial gastrocnemius (P < 0.01), but not for the lateral gastrocnemius (P = 0.84) and soleus (P = 0.50).

Discussion

The purpose of the present study was to compare plantar flexors muscle activation during SJ and MJ exercises in trained men, here represented by calf raise and leg press exercises, respectively. Our main finding is that there was no difference for muscle activation for any muscle analyzed. This agrees with previous findings in upper and lower body muscles and confirms the suggestion that plantar flexors have a great involvement in lower body MJ exercises; however, the results were, to some extent, unexpected.

Plantar flexion is performed mainly by the 3 muscles that compose the triceps surae: soleus, medial, and lateral gastrocnemius. Soleus is originated in the tibia and fibula and inserted in the calcaneus, crossing only one joint. Considering that it acts mainly in the ankle and that both the leg press and calf raises exercises have a similar range of motion in that joint, the similar levels of muscle activation was not surprising. However, the medial and lateral gastrocnemius cross the knee and ankle joints, as they are originated in the femur and inserted in the calcaneus. Therefore, the gastrocnemius would have antagonistic actions during the leg press, as they flex the knee and extend the ankle, which is known as the Lombard Paradox. Considering that the shortening in one joint is accompanied by the lengthening at the other, it was expected that the gastrocnemius activation would be decreased during the leg press. However, this was not the case. Considering that the calf muscles might act as dynamic knee stabilizers, one possible explanation is that the muscle contracted mainly isometrically, which can increase activation, as previously suggested.

To the best of our knowledge, this is the first study to compare calf muscle activation between MJ and SJ exercises. The present results have many potentially important applications, since exercises oriented for the plantar flexors might be useful in chronic venous insufficiency and venous leg ulcers, rehabilitation, orthostatic tolerance, balance, prevention of falls, and functionality. Based on our results, one can choose between MJ and SJ exercises when aiming at activating the plantar flexors. It is interesting to note that previous studies showed that MJ exercises, like leg press and squat, are able to promote adaptations in quadriceps, hamstrings, and gluteus. If lower body MJ exercises prove to be efficient also for plantar flexors, they can provide a time-efficient approach, since their performance can be sufficient to train most lower body muscles.

We acknowledge that caution is required when extrapolating an acute effect onto a chronic change.

Whilst some studies suggest that activation might be important for muscle adaptations, others suggest that electromyography cannot be necessarily linked to gains in muscle size and strength. However, it has been suggested that mechanotransduction is likely to occur only in muscle fibers activated during exercise. This suggests that high levels of muscle activation produced from repeated contractions can provide stimulation to the muscle, especially when combined with other factors, such as mechanical and metabolic stress, muscle swelling, etc. Therefore, the present study can provide a rationale for further studies aimed at comparing the long-term effects of MJ and SJ exercises in plantar flexors’ function and morphology.

Based on the results of the present study, the leg press exercise can be recommended to promote muscle activation of the plantar flexors similarly to calf raises. Considering that MJ exercise involves other muscles such as quadriceps, hamstrings, and gluteus, exercise professionals should consider their use as a time efficient approach for exercise prescription.

This excerpt is from Gentil P, Souza D, Santana M, et al. Multi- and Single-Joint Resistance Exercises Promote Similar Plantar Flexor Activation in Resistance Trained Men. Int J Environ Res Public Health. 2020;17:9487. Editing has occurred; references were deleted due to space limitations. Use is per the Creative Commons license 4.0. Readers are encouraged to read the full article online at https://doi.org/10.3390/ijerph17249487.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.