Homogeneity of fascicle architecture following repeated contractions in the human gastrocnemius medialis

Running 40 Minutes under Temperate or Hot Environment Does Not Affect Operating Fascicle Length

PURPOSE

Muscle mechanics is paramount in our understanding of motor performance. However, little is known regarding the sensitivity of fascicle dynamics and connective tissues stiffness to exercise duration and ambient temperature during running, both increasing muscle temperature. This study aimed to determine gastrocnemius medialis (GM) fascicle dynamics in vivo during running in temperate and hot conditions, as well as muscle-tendon unit responses.

METHODS

Using ultrafast ultrasound, 15 participants (8 men, 7 women; 26 ± 3 yr) were tested before, during (2 and 40 min), and after a running task (40 min at 10 km·h -1 ) in temperate (TEMP; ~23°C) and hot (HOT: ~38°C) conditions.

RESULTS

Although core, skin temperatures, and heart rate increased from the beginning to the end of the exercise and in a larger extent in HOT than TEMP ( P < 0.001), the physiological stress elicited did not alter running temporal parameters and GM fascicle operating lengths, with similar behavior of the fascicles on their force-length relationship, over time (2 vs 40 min) or across condition (TEMP vs HOT; P ≥ 0.248). Maximal voluntary force production did not reported statistical changes after exercise ( P = 0.060), and the connective tissues stiffness measured (i.e., passive muscle and stiffness of the series-elastic elements) did not show neither time ( P ≥ 0.281), condition ( P ≥ 0.256) nor time-condition interaction ( P ≥ 0.465) effect.

CONCLUSIONS

This study revealed that prolonged running exercise does not alter muscle-tendon unit properties and interplay, which are not influenced by ambient temperature. These findings may rule out potential detrimental effects of heat on muscle properties and encourage further investigations on longer and more intense running exercise.

Behavior of medial gastrocnemius muscle beneath kinesio taping during isometric contraction and badminton lunge performance after fatigue induction

Kinesio taping (KT) is widely used in sports for performance improvement and injury prevention. However, little is known of the behavior of the muscle region beneath the KT with movement, particularly when the muscle is fatigued. Accordingly, this study investigated the changes in the medial gastrocnemius muscle architecture and fascia thickness when using KT during maximum isometric plantar flexion (MVIC) and badminton lunges following heel rise exercises performed to exhaustion. Eleven healthy collegiate badminton players (4 males and 7 females) were recruited. All of the participants performed two tasks (MVIC and badminton lunge) with a randomized sequence of no taping, KT and sham taping and repeated following exhaustive repetitive heel rise exercise. In the MVIC task, the fascia thickness with the medial gastrocnemius muscle at rest significantly decreased following fatigue induction both without taping and with KT and sham taping (p = 0.036, p = 0.028 and p = 0.025, respectively). In the lunge task, the fascia thickness reduced after fatigue induction in the no taping and sham taping trials; however, no significant change in the fascia thickness occurred in the KT trials. Overall, the results indicate that KT provides a better effect during dynamic movement than in isometric contraction.

The Anticipation of Gravity in Human Ballistic Movement

Stretch-shortening type actions are characterized by lengthening of the pre-activated muscle-tendon unit (MTU) in the eccentric phase immediately followed by muscle shortening. Under 1 g, pre-activity before and muscle activity after ground contact, scale muscle stiffness, which is crucial for the recoil properties of the MTU in the subsequent push-off. This study aimed to examine the neuro-mechanical coupling of the stretch-shortening cycle in response to gravity levels ranging from 0.1 to 2 g. During parabolic flights, 17 subjects performed drop jumps while electromyography (EMG) of the lower limb muscles was combined with ultrasound images of the gastrocnemius medialis, 2D kinematics and kinetics to depict changes in energy management and performance. Neuro-mechanical coupling in 1 g was characterized by high magnitudes of pre-activity and eccentric muscle activity allowing an isometric muscle behavior during ground contact. EMG during pre-activity and the concentric phase systematically increased from 0.1 to 1 g. Below 1 g the EMG in the eccentric phase was diminished, leading to muscle lengthening and reduced MTU stretches. Kinetic energy at take-off and performance were decreased compared to 1 g. Above 1 g, reduced EMG in the eccentric phase was accompanied by large MTU and muscle stretch, increased joint flexion amplitudes, energy loss and reduced performance. The energy outcome function established by linear mixed model reveals that the central nervous system regulates the extensor muscles phase- and load-specifically. In conclusion, neuro-mechanical coupling appears to be optimized in 1 g. Below 1 g, the energy outcome is compromised by reduced muscle stiffness. Above 1 g, loading progressively induces muscle lengthening, thus facilitating energy dissipation.

Medial Gastrocnemius Muscle Architecture Is Altered After Exhaustive Stretch-Shortening Cycle Exercise

Muscle architecture is an important component of muscle function, and recent studies have shown changes in muscle architecture with fatigue. The stretch-shortening cycle is a natural way to study human locomotion, but little is known about how muscle architecture is affected by this type of exercise. This study investigated potential changes in medial gastrocnemius (MG) muscle architecture after exhaustive stretch-shortening cycle exercise. Male athletes (n = 10) performed maximal voluntary contractions (MVC) and maximal drop jump (DJ) tests before and after an exercise task consisting of 100 maximal DJs followed by successive rebound jumping to 70% of the initial maximal height. The exercise task ceased upon failure to jump to 50% of maximal height or volitional fatigue. Muscle architecture of MG was measured using ultrasonography at rest and during MVC, and performance variables were calculated via a force plate and motion analysis. After SSC exercise, MVC (−13.1%; p = 0.005; d_z = 1.30), rebound jump height (−14.8%, p = 0.004; d_z = 1.32), and ankle joint stiffness (−26.3%; p = 0.008; d_z = 1.30) decreased. Ankle joint range of motion (+20.2%; p = 0.011; d_z = 1.09) and MG muscle-tendon unit length (+12.0%; p = 0.037; d_z = 0.91) during the braking phase of DJ, the immediate drop-off in impact force (termed peak force reduction) (Δ27.3%; p = 0.033; d_z = 0.86), and lactate (+9.5 mmol/L; p < 0.001; d_z = 3.58) increased. Fascicle length increased at rest (+4.9%; p = 0.013; d_z = 1.16) and during MVC (+6.8%; p = 0.048; d_z = 0.85). Pennation angle decreased at rest (−6.5%; p = 0.034, d_z = 0.93) and during MVC (−9.8%; p = 0.012; d_z = 1.35). No changes in muscle thickness were found at rest (−2.6%; p = 0.066; d_z = 0.77) or during MVC (−1.6%; p = 0.204; d_z = 0.49). The greater MG muscle-tendon stretch during the DJ braking phase after exercise indicates that muscle damage likely occurred. The lower peak force reduction and ankle joint stiffness, indicative of decreased active stiffness, suggests activation was likely reduced, causing fascicles to shorten less during MVC.

Medial gastrocnemius muscle-tendon interaction and architecture change during exhaustive hopping exercise

BACKGROUND

Previous literature has shown in vivo changes in muscle-tendon interaction during exhaustive stretch-shortening cycle (SSC) exercise. It is unclear whether these changes in muscle-tendon length during exhaustive SSC exercise are associated with changes in mechanical efficiency (ME). The purpose of the study was to investigate whether changes in platarflexor contractile component (CC) length, tendon length, and changes in plantarflexor muscle activity could explain reduction in ME during exhaustive SSC exercise.

METHODS

Eight males participated in an exhaustive hopping task to fatigue. Mechanical work and energy expenditure were calculated at different time-points during the hopping task. Furthermore, hopping kinetics and kinematics, medial gastrocnemius (MG) muscle activity, and in vivo ultrasound of the MG were also collected at different time-points throughout the hopping task.

RESULTS

ME did not change during the hopping protocol despite shorter tendon and longer CC lengths as subjects approached exhaustion. Percent decreases in pennation angle and muscle thickness were most strongly correlated to time to exhaustion (r=0.94, p⩽0.05; r=0.87, p⩽0.05; respectively). Percent changes in CC length change and pennation angle were strongly correlated to percent decrease in maximal voluntary isometric plantarflexion (MVIP) force (r=-0.71, p⩽0.04; r=0.70, p⩽0.05; respectively). Braking/push-off EMG ratio increased from initial pre-fatigue values to all other time points showing neuromuscular adaptations to altered muscle lengths.

CONCLUSION

Findings from the current study suggest that changes in CC and tendon lengths occur during repetitive hopping to exhaustion, with the amount change strongly related to time to exhaustion. ME of hopping remained unchanged in the presence of altered CC and tendon lengths.