Effect of ankle joint stiffness during eccentric phase in rebound jumps on ankle joint torque at midpoint

Effects of progressive weight addition using vests on rebound jump

BACKGROUND

Rebound jump (RJ) is an exercise that is as short contact time and high as possible and is used to improve lower limb stretch-shortening cycle movements. This study examined the effects of RJ performance and lower limb joint kinetics when weight was incrementally added using a weighted vest.

METHODS

Eleven male athletes (mean±standard deviation: age, 21.9±1.6 years; height, 176.3±5.5 cm; weight, 67.8±4.2 kg) performed RJ at 0% (no load), 5%, 9%, 12%, 15%, 18%, and 21% added weight. Body coordinates and ground reaction force were measured, and RJ index (jump height / contact time) and joint kinetics (joint torque, power, and work) were calculated.

RESULTS

One-way Analysis of Variance showed that the RJ was significantly reduced starting from 12% (P<0.01), the jump height was significantly decreased starting from 12% (P<0.01), and the contact time was significantly increased only at 21% (P<0.01) compared with 0%. The negative peak power of the ankle joint decreased by 21% of the added weight (P<0.01). The main effects of body weight on the peak torque at the knee and hip joints and the positive peak power at the knee joint were observed.

CONCLUSIONS

RJ with increasing weight tended to decrease jump height first, rather than longer contact time. However, it was suggested that there is an appropriate range of added weights that can be trained without decreasing the RJ index.

Characteristics of three lower limb joint kinetics affecting rebound jump performance

The stretch-shortening cycle (SSC) motor execution ability of the lower limb was measured using the rebound jump index (RJ-index) in RJ test; this performance is influenced by the interaction of the forces exerted by the three joints of the lower limb.We aimed to determine RJ performance variables and identify the lower limb kinetic variables that affect them. One hundred two female university students (age, 20.1±1.0 years; height, 164.6±7.2 cm; mass, 58.9±7.3 kg) for whom RJ performance variables (RJ-index, jump height, and contact time) and joint kinetics (torque, power, and work) were measured. Statistical analysis showed a strong correlation between the RJ-index and jump height or contact time (r = 0.920, -0.726, p < 0.05) but a weak correlation between the jump height and contact time (r = -0.384, p < 0.05). Furthermore, positive ankle power was the most influential factor for RJ performance variables; additionally, positive knee power and hip work and eccentric knee torque significantly influenced jump height, and positive ankle power, negative work and power, and concentric torque significantly influenced the contact time. The acquisition of the jump height and a shorter contact time requires different kinetic variables. Furthermore, the characteristics of the force exerted by the three joints of the lower limb that compose the RJ-index may be different even if the RJ-index has the same value. Therefore, by assessing not only the RJ-index but also the jump height, contact time, and characteristics of lower limb joint kinetics in the RJ test, it is possible to conduct effective training to improve lower limb SSC motor execution performance according to individual characteristics.

Relationship Between Drop Jump Training–Induced Changes in Passive Plantar Flexor Stiffness and Explosive Performance

Passive muscle stiffness is positively associated with explosive performance. Drop jump training may be a strategy to increase passive muscle stiffness in the lower limb muscles. Therefore, the purpose of this study was to examine the effect of 8-week drop jump training on the passive stiffness in the plantar flexor muscles and the association between training-induced changes in passive muscle stiffness and explosive performance. This study was a randomized controlled trial. Twenty-four healthy young men were divided into two groups, control and training. The participants in the training group performed drop jumps (five sets of 20 repetitions each) 3days per week for 8weeks. As an index of passive muscle stiffness, the shear moduli of the medial gastrocnemius and soleus were measured by shear wave elastography before and after the intervention. The participants performed maximal voluntary isometric plantar flexion at an ankle joint angle of 0° and maximal drop jumps from a 15cm high box. The rate of torque development during isometric contraction was calculated. The shear modulus of the medial gastrocnemius decreased for the training group (before: 13.5±2.1kPa, after: 10.6±2.1kPa); however, such a reduction was not observed in the control group. There was no significant group (control and training groups)×time (before and after the intervention) interaction for the shear modulus of the soleus. The drop jump performance for the training group improved, while the rate of torque development did not change. Relative changes in these measurements were not correlated with each other in the training group. These results suggest that drop jump training decreases the passive stiffness in the medial gastrocnemius, and training-induced improvement in explosive performance cannot be attributed to change in passive muscle stiffness.

How Compliance of Surfaces Affects Ankle Moment and Stiffness Regulation During Walking

Humans can regulate ankle moment and stiffness to cope with various surfaces during walking, while the effect of surfaces compliance on ankle moment and stiffness regulations remains unclear. In order to find the underlying mechanism, ten healthy subjects were recruited to walk across surfaces with different levels of compliance. Electromyography (EMG), ground reaction forces (GRFs), and three-dimensional reflective marker trajectories were recorded synchronously. Ankle moment and stiffness were estimated using an EMG-driven musculoskeletal model. Our results showed that the compliance of surfaces can affect both ankle moment and stiffness regulations during walking. When the compliance of surfaces increased, the ankle moment increased to prevent lower limb collapse and the ankle stiffness increased to maintain stability during the mid-stance phase of gait. Our work improved the understanding of gait biomechanics and might be instructive to sports surface design and passive multibody model development.

Relationship between resting medial gastrocnemius stiffness and drop jump performance

Although the influence of the series elastic element of the muscle-tendon unit on jump performance has been investigated, the corresponding effect of the parallel elastic element remains unclear. This study examined the relationship between the resting calf muscle stiffness and drop jump performance. Twenty-four healthy men participated in this study. The shear moduli of the medial gastrocnemius and the soleus were measured at rest as an index of muscle stiffness using ultrasound shear wave elastography. The participants performed drop jumps from a 15 cm high box. The Spearman rank correlation coefficient was used to examine the relationships between shear moduli of the muscles and drop jump performance. The medial gastrocnemius shear modulus showed a significant correlation with the drop jump index (jump height/contact time) (r = 0.414, P = 0.044) and jump height (r = 0.411, P = 0.046), but not with contact time (P > 0.05). The soleus shear modulus did not correlate with these jump parameters (P > 0.05). These results suggest that the resting medial gastrocnemius stiffness can be considered as one of the factors that influence drop jump performance. Therefore, increase in resting muscle stiffness should enhance explosive athletic performance in training regimens.

The Effects of Cold Water Immersion on the Recovery of Drop Jump Performance and Mechanics: A Pilot Study in Under-20 Soccer Players

Cold water immersion (CWI) is a popular method used for enhancing recovery from exercise. However, the efficacy of this approach is inconclusive and studies investigating variables contributing to overall performance are scarce. Additionally, few studies have investigated the recovery of stretch-shortening cycle (SSC) performance after a fatiguing SSC task. The SSC occurs naturally in human locomotion and induces a recovery pattern different from isolated muscle contractions (e.g., pure eccentric exercise). Therefore, the main aim of this study was to investigate the effects of a single CWI on jumping performance and mechanics after exhaustive SSC exercise. On a sledge apparatus, 10 male under-20 soccer players (age 18–20 years) performed five sets of 20 maximal drop jumps (DJ) followed by continuous submaximal rebounding. Subjects were equally randomized into a passive recovery control (CON) or CWI group (10 ± 0.5°C for 20 min). Prior to, upon completion of, and at 24 and 48 h follow-ups, subjects performed maximal DJs recorded with a high-speed video camera. Blood samples were taken and subjective muscle soreness was measured. Rebound jump height was impaired immediately after exercise, although significant only for CWI (CON: −12.4 cm, p = 0.083; CWI: −9.9 cm, p = 0.009). The CWI group demonstrated significant recovery of jump height at 24 h (+6.3 cm, p = 0.031) and 48 h (+8.9 cm, p = 0.002) compared to post-exercise. Ankle joint stiffness was decreased for CWI (−2.1 to −2.5 Nm/°, p = 0.005–0.041). Creatine kinase activity was similarly increased for both groups at 24 and 48 h, while there was also no group effect in muscle soreness (p ≥ 0.056). This pilot study demonstrates the potential for CWI to slightly enhance the recovery of DJ performance. However, this occurred in parallel with reduced ankle joint stiffness, signifying that jumps were performed with less efficiency, which would not be favorable for repeated SSC actions. While this should be confirmed with a larger sample size, this highlights the potential for CWI to be detrimental to the mechanical properties of the ankle joint. Therefore, future recovery intervention studies should concomitantly investigate variables contributing to performance, rather than just overall performance itself.

Assessing the Effects of Kata and Kumite Techniques on Physical Performance in Elite Karatekas

This study aimed at assessing physical performance of elite karatekas and non-karatekas. More specifically, effects of kumite and kata technique on joint mobility, body stability, and jumping ability were assessed by enrolling twenty-four karatekas and by comparing the results with 18 non-karatekas healthy subjects. Sensor system was composed by a single inertial sensor and optical bars. Karatekas are generally characterized by better motor performance with respect nonkaratekas, considering all the examined factors, i.e., mobility, stability, and jumping. In addition, the two techniques lead to a differentiation in joint mobility; in particular, kumite athletes are characterized by a greater shoulder extension and, in general, by a greater value of preferred velocity to perform joint movements. Conversely, kata athletes are characterized by a greater mobility of the ankle joint. By focusing on jumping skills, kata technique leads to an increase of the concentric phase when performing squat jump. Finally, kata athletes showed better stability inclosed eyes condition. The outcomes reported here can be useful for optimizing coaching programs for both beginners and karatekas based on the specific selected technique.

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.

Interday Reliability and Usefulness of a Reactive Strength Index Derived From 2 Maximal Rebound Jump Tests

PURPOSE

To examine the interday reliability and usefulness of a reactive strength index (RSI) derived from a maximal 5-rebound jump test (5max RJT) and a maximal 10-rebound jump test (10/5 RJT).

METHODS

Twenty male field-sport athletes (24.5 [3.0] y, 1.78 [0.1] m, 84.9 [5.2] kg) and 15 female participants (21.1 [0.9] y, 1.65 [0.73] m, 62.0 [5.1] kg) performed 2 maximal repetitions of the 5max RJT and the 10/5 RJT on 2 testing days after a specific warm-up. A 1-wk period separated testing days, and these sessions were preceded by a familiarization session. RSI was calculated by dividing jump height (in meters) by contact time (in seconds). The 5max RJT and the 10/5 RJT trial with the highest RSI on each testing day were used for reliability and usefulness analysis.

RESULTS

Both tests were deemed reliable for determining RSI for male, female, and pooled male and female cohorts, as the intraclass correlation coefficients were ≥.80 and the coefficient of variation was ≤10%. Only the 5max RJT was rated as "good" at detecting the smallest worthwhile change in performance for female athletes (smallest worthwhile change: 0.10 > typical error: 0.07). The 5max RJT for men and the 10/5 RJT for men and women were rated "good" in detecting a moderate change in performance only.

CONCLUSIONS

Both tests are reliable for the determination of RSI, but the usefulness of the tests in detecting the smallest worthwhile change is questionable.

Effect of Jump Direction on Joint Kinetics of Take-Off Legs in Double-Leg Rebound Jumps

Vertical (VDJ) and horizontal (HDJ) double-leg rebound jumps are used as plyometric exercises in direction-specific training regimens for various sports. We investigated the effects of jump direction on joint kinetics of the take-off legs in double-leg rebound jumps. Twelve Japanese male track and field athletes performed VDJ, 100% HDJ, 50% HDJ (50% of 100% HDJ distance), and 75% HDJ (75% of 100% HDJ distance). Kinematic and kinetic data in the sagittal plane were calculated using a force platform and high-speed video camera. Hip negative power during the eccentric phase decreased from VDJ to 50% HDJ (VDJ, -4.40 ± 4.25 W/kg; 50% HDJ, -0.83 ± 2.10; 75% HDJ, -0.33 ± 0.83; 100% HDJ, 0 ± 0), while hip positive power increased from VDJ to 100% HDJ (VDJ, 4.19 ± 2.73 W/kg; 50% HDJ, 9.37 ± 2.89; 75% HDJ, 11.15 ± 3.91; 100% HDJ, 18.51 ± 9.83). Knee negative power increased from VDJ to 75% HDJ (VDJ, -14.48 ± 7.67 W/kg; 50% HDJ, -18.98 ± 7.13; 75% HDJ, -21.57 ± 8.54; 100% HDJ, -23.34 ± 12.13), while knee positive power decreased from VDJ to 75% HDJ (VDJ, 23.18 ± 9.01 W/kg; 50% HDJ, 18.83 ± 5.49; 75% HDJ, 18.10 ± 5.77; 100% HDJ, 16.27 ± 6.22). Ankle joint kinetics remained unchanged. Differences in hip and knee joint kinetics between VDJ and HDJ were associated with direction control, becoming more pronounced as jump distance increased.

Joint laxity is related to lower extremity energetics during a drop jump landing

PURPOSE

To examine the relationships between anterior knee laxity (AKL), genu recurvatum (GR), and general joint laxity (GJL) with sagittal plane energetics in males and females during a drop jump task.

METHODS

A total of 68 females and 50 males were measured for AKL, GR, and GJL and were instrumented to obtain neuromuscular and biomechanical data on their dominant limb during the initial landing phase of a 45-cm drop jump. Multiple linear regressions determined the extent to which the three joint laxity variables combined to predict hip, knee, and ankle work absorption and stiffness. Associations between joint laxity and joint kinematics, joint kinetics, and muscle activation amplitudes were also investigated to further interpret significant relationships.

RESULTS

Higher AKL and GJL and lower GR combined to predict greater knee work absorption (R2 = 0.210, P = 0.002) and stiffness (R2 = 0.127, P = 0.033) and lower ankle stiffness (R2 = 0.115, P = 0.048) in females. These associations were modulated through greater peak knee extensor moments and flexion angles, lower hamstring activation, and lower ankle extensor moments. In males, joint laxity had little impact on knee energetics, but a significant association was observed between greater GJL and decreased ankle stiffness (R2 = 0.209, P = 0.012), a product of both greater peak ankle flexion and decreased ankle extensor moment.

CONCLUSIONS

Females with greater AKL and GJL and lower GR demonstrated a landing strategy that increased work absorption and stiffness about the knee, whereas females with greater GR demonstrated a landing style that reduced knee work absorption and stiffness. The findings suggest that AKL, GR, and GJL may represent distinct risk factors and support the need to consider more comprehensive laxity profiles as they relate to knee joint function and anterior cruciate ligament injury risk.

Age-related muscle activation profiles and joint stiffness regulation in repetitive hopping

It is well documented that increasing effort during exercise is characterized by an increase in electromyographic activity of the relevant muscles. How aging influences this relationship is a matter of great interest. In the present study, nine young and 24 elderly subjects did repetitive hopping with maximal effort as well as with 50%, 65%, 75% and 90% intensities. During hopping joint kinematics were measured together with electromyographic activity (EMG) from the soleus, gastrocnemius medialis, gastrocnemius lateralis and tibialis anterior muscles. The results showed that agonist activation increased in both age groups with increasing intensity. The highest jumping efficiency (EMG ratio of the braking phase to the push off-phase activation) was achieved with moderate hopping intensities (65-75%) in both the young and in the elderly. Age-comparison showed that elderly subjects had high agonist preactivation but thereafter lower activation during the braking phase. Antagonist coactivation was minimal and did not show age- or intensity-specificity. The elderly had more flexed knees at the instant of ground contact. When intensity increased, the elderly also plantarflexed their ankles more before ground contact. Ankle joint stiffness was lower in elderly subjects only in high hopping intensities (90% and Max). These results confirm that age-specific agonist muscle activation profiles exist during hopping even when exercise intensities are matched on the relative scale. The results suggest further that the elderly can adjust their reduced neuromuscular capacity to match the demands set by different exercise intensities.

Neuromuscular differences between prepubescents boys and adult men during drop jump

The purpose of the present study was to determine the lower extremities biomechanical differences between prepubescent and adult males during drop jumps (DJs). Twenty-four untrained males (12 prepubescents, 12 adults) performed DJs from 20 cm height. Kinematics of the lower extremities were captured, in addition with vertical ground reaction forces (vGRFs) and EMG activity of the gastrocnemius medialis (GM), soleus (SOL) and tibialis anterior (TA) muscles. The results showed that men jumped higher, as expected, but their knees were more flexed prior to landing, and their preactivation level was higher and longer in duration compared to prepubescent boys. During landing, men had shorter contact times, lower vGRF normalized to body mass, and less maximal knee joint flexion. Regarding EMG activity men presented higher stretch reflex and higher EMG activity during the braking phase but the level of coactivation (TA to GM + SOL ratio) was lower. It is seems that pre-landing and landing patterns during a complex task such as DJ are affected by physical development. There are indications that men had higher performance in a DJ than prepubescent boys because they activated more effectively their muscles during the preactivation and braking phase. The above-mentioned data support the hypothesis that prepubescent boys might be inferior in optimal regulation of their muscle-tendon unit stiffness.

Age-related neuromuscular function during drop jumps

Muscle- and movement-specific fascicle-tendon interaction affects the performance of the neuromuscular system. This interaction is unknown among elderly and consequently contributes to the lack of understanding the age-related problems on neuromuscular control. The present experiment studied the age specificity of fascicle-tendon interaction of the gastrocnemius medialis (GM) muscle in drop jump (DJ) exercises. Twelve young and thirteen elderly subjects performed maximal squat jumps and DJs with maximal rebound effort on a sledge apparatus. Ankle and knee joint angles, reaction force, and electromyography (EMG) from the soleus (Sol), GM, and tibialis anterior (TA) muscles were measured together with the GM fascicle length by ultrasonography. The results showed that the measured ankle joint stiffness (AJS) during the braking phase correlated positively with the rebound speed in both age groups and that both parameters were significantly lower in the elderly than in young subjects. In both groups, the AJS correlated positively with averaged EMG (aEMG) in Sol during the braking phase and was further associated with GM activation (r = 0.55, P < 0.01) and TA coactivation (TA/GM r = -0.4 P < 0.05) in the elderly subjects. In addition, compared with the young subjects, the elderly subjects showed significantly lower GM aEMG in the braking phase and higher aEMG in the push-off phase, indicating less utilization of tendinous tissue (TT) elasticity. These different activation patterns are in line with the mechanical behavior of GM showing significantly less fascicle shortening and relative TT stretching in the braking phase in the elderly than in the young subjects. These results suggest that age-specific muscle activation patterns as well as mechanical behaviors exist during DJs.