Accelerated rehabilitation for anterior cruciate ligament (ACL) injury and reconstruction surgery is designed to return injured people to athletic activities in approximately 6 months. The small amount of empirical data on this population suggests, however, that the torque at the knee joint may not return until 22 months after surgery during walking and even longer during running. Although the rehabilitation has ended and individuals have returned to preinjury activities, gait mechanics appear to be abnormal at the end of accelerated programs. The purpose of this study was to compare lower extremity joint kinematics, kinetics, and energetics between individuals having undergone ACL reconstruction and accelerated rehabilitation and healthy individuals.Eight ACL-injured and 22 healthy subjects were tested. Injured subjects were tested 3 wk and 6 months (the end of rehabilitation) after surgery. Ground reaction force and kinematic data were combined with inverse dynamics to predict sagittal plane joint torques and powers from which angular impulse and work were derived.The difference in all kinematic variables between the two tests for the ACL group averaged 38% (all P < 0.05). The kinematics were not different between the ACL group after rehabilitation and healthy subjects. Angular impulses and work averaged 100% difference for all joints (all P < 0.05) between tests for the ACL group. After rehabilitation, the differences between injured and healthy groups in angular impulse and work at both the hip and knee remained large and averaged 52% (all P < 0.05).Results indicated that after reconstruction surgery and accelerated rehabilitation for ACL injury, humans walk with normal kinematic patterns but continue to use altered joint torque and power patterns.
Resistance training (RT) improves the skeletal muscle’s ability to generate maximal voluntary force and is accompanied by changes in the activation of the antagonist muscle which is not targeted primarily by RT. However, the nature and role of neural adaptation to RT in the antagonist muscle is paradoxical and not well understood. We compared moments, agonist muscle activation, antagonist activation, agonist-antagonist coactivation, and electromyographic (EMG) model-predicted moments generated by antagonist hamstring muscle coactivation during isokinetic knee extension in leg strength-trained (n = 10) and untrained (n = 11) healthy, younger adults. Trained vs. untrained adults were up to 58% stronger. During knee extension, hamstring activation was 1.6-fold greater in trained vs. untrained adults (p = 0.022). This hamstring activation produced 2.6-fold greater model-predicted antagonist moments during knee extension in the trained (42.7 ± 19.55 Nm) vs. untrained group (16.4 ± 12.18 Nm; p = 0.004), which counteracted (reduced) quadriceps knee extensor moments ~43 Nm (0.54 Nm·kg−1) and by ~16 Nm (0.25 Nm·kg−1) in trained vs. untrained. Antagonist hamstring coactivation correlated with decreases and increases, respectively, in quadriceps moments in trained and untrained. The EMG model-predicted antagonist moments revealed training history-dependent functional roles in knee extensor moment generation.
ABSTRACT Introduction/Purpose Little is known about the comparative effectiveness of exercise programs, especially when delivered at a high intensity, in mobility-limited older adults. We compared the effects of 25 sessions of high-intensity agility exergaming (EXE) and stationary cycling (CYC) at the same cardiovascular load on measured and perceived mobility limitations, balance, and health-related quality of life in mobility-limited older adults. Methods Randomized to EXE ( n = 28) and CYC ( n = 27), mobility-impaired older adults (age 70 yr) exercised five times per week for 5 wk at 80% of age-predicted maximal heart rate. Waitlisted controls did not exercise ( n = 28). Results Groups did not differ at baseline in any outcomes ( P > 0.05). The primary outcomes (The Short Form-36-Health Survey: EXE, 6.9%; effect size, 2.2; CYC, 5.5%, 1.94; Western Ontario and McMaster Universities Osteoarthritis Index: EXE, −27.2%, −3.83; CYC, −17.2, −2.90) improved similarly ( P > 0.05). Secondary outcomes, including body mass (−3.7%), depression (−18%), and walking capacity (13.5%) also improved ( P < 0.05) similarly after the two interventions. Activities of daily living, Berg Balance Score, BestTest scores, and Dynamic Gait Index improved more ( P < 0.05) after EXE than CYC. Center of pressure of standing sway path improved in one of six tests only after EXE ( P < 0.05). Postexercise cardiovascular response improved in EXE ( P = 0.019). CON did not change in any outcomes ( P > 0.05). Conclusions When matched for cardiovascular and perceived effort, two diverse high-intensity exercise programs improved health-related quality of life, perceived mobility limitation, and walking capacity similarly and balance outcomes more in mobility-limited older adults, expanding these older adults’ evidence-based exercise options to reduce mobility limitations.
One manifestation of advancing age altering movement control is that old vs young adults execute movements with higher agonist-antagonist co-activation. An analysis of muscle-to-muscle coherence, the similarity between a pair of signals in the frequency domain, could reveal if age modifies the common synaptic input from spinal and cortical sources, respectively, to muscle pairs in the alpha (∼10 Hz) and beta (∼30 Hz) frequency bands, and mediate the increased co-activation. PURPOSE: To determine if there are changes in the EMG coherence between agonist and antagonist leg muscles of young and old adults during walking. METHODS: In this pilot study, 2 young (age 23 and 24) and 2 old adults (age 79 and 81) walked at 2 and 3 mph on a treadmill. Surface EMG activity (16-500 Hz) was collected at 1 kHz from the vastus lateralis, biceps femoris, gastrocnemius lateralis, and tibialis anterior using a telemetric system. Cross-correlation, coherence, and its 95th confidence limit were computed in a 200-ms window before and after heel strike for 300 steps. RESULTS: Averaged in BF/VL and TA/GS muscle pairs and the 2 speeds, co-activation in old vs young was 26% and 11 %. Both old but neither young adults exhibited significant (p < 0.05) coherence at ∼10 Hz between the VL and BF in the stance and swing phase at 2 and 3 mph. All subjects showed coherence at ∼10 Hz between the GS and TA but old adults had more coherence in the swing phase at both speeds. In control experiments in young subjects there was coherence (p < 0.05) across the frequency spectrum when EMG was recorded during an isometric contraction from 2 electrodes placed on the same muscle. Thus, cross-talk between muscle pairs probably did not contaminate the coherence observed during walking. CONCLUSION: These initial results indicate that age may modify the common synaptic input from spinal and cortical sources to muscle pairs and this adaptation may underlie the increased co-activation. Supported by NIH grants AG024161, NS049783.
ABSTRACT Introduction The ability to adapt dynamic balance to perturbations during gait deteriorates with age. To prevent age-related decline in adaptive control of dynamic balance, we must first understand how adaptive control of dynamic balance changes across the adult lifespan. We examined how adaptive control of the margin of stability (MoS) changes across the lifespan during perturbed and unperturbed walking on the split-belt treadmill. Methods Seventy-five healthy adults (age range, 18–80 yr) walked on an instrumented split-belt treadmill with and without split-belts. Linear regression analyses were performed for the mediolateral (ML) and anteroposterior (AP) MoS, step length, single support time, step width, double support time, and cadence during unperturbed and perturbed walking (split-belt perturbation), with age as predictor. Results Age did not significantly affect dynamic balance during unperturbed walking. However, during perturbed walking, the ML MoS of the leg on the slow belt increased across the lifespan due to a decrease in bilateral single support time. The AP MoS did not change with aging despite a decrease in step length. Double support time decreased and cadence increased across the lifespan when adapting to split-belt walking. Age did not affect step width. Conclusions Aging affects the adaptive control of dynamic balance during perturbed but not unperturbed treadmill walking with controlled walking speed. The ML MoS increased across the lifespan, whereas bilateral single support times decreased. The lack of aging effects on unperturbed walking suggests that participants’ balance should be challenged to assess aging effects during gait. The decrease in double support time and increase in cadence suggests that older adults use the increased cadence as a balance control strategy during challenging locomotor tasks.
Obesity is characterized by increased body mass relative to height. Surprisingly obese vs lean adults can walk on level surface by increasing only ankle power. Incline walking however requires greater hip power in lean adults suggesting that gait adaptations in obese vs lean adults may be task dependent. PURPOSE: Compare lower extremity joint work in obese and lean adults during incline and decline walking. METHODS: 3D ground forces and kinematics were measured in 20 obese (119 kg, 40 kg/m2) and 20 lean (71 kg, 23 kg/m2) adults during 10° incline and decline walking at 1.5 m/s. Joint work and selected kinematic variables were analyzed with 2 × 2 mixed model ANOVA and post hoc tests, p<.05. RESULTS: Significant interactions for stride length (SL) and vertical displacement per step (both p=.015) showed lean had 0.17 m longer strides (p=0.002) and 0.017 m greater displacement (p=0.008) in incline but statistically equal SL and displacement in decline. Significant interaction (p=.014) for joint work summed over hip, knee, and ankle showed lean generated 20% more energy in incline (p=0.001) but dissipated statistically equal energy in decline. Hip (p=.001) and ankle (p=.011) work also significantly interacted between body mass and surface slope. Lean generated 32% more energy at the hip in incline (p=.002) while obese dissipated 237% more energy at the hip in decline (p=0.002). We note however that energy dissipation at the hip was low in decline walking and the lean-obese difference may not be physiological meaningful. Lean generated 17% more energy at the ankle in incline (p=.008) while obese dissipated 34% more energy at the ankle in decline (p=.038). CONCLUSION: The difference of increased body mass relative to height produced a complex response in gait adaptations that are task dependent. Full understanding of biomechanical outcomes of obesity therefore requires comprehensive biomechanical investigations.TABLE
The purpose of this study was to determine the effects of training load (25% vs. 75% of one repetition maximum [1RM]) and fatigue (failure vs. non-failure) during four weeks of unilateral knee extension resistance training (RT) on maximal voluntary force in the trained and the untrained knee extensors. Healthy young adults (n = 42) were randomly assigned to control (CON, n = 9, 24 ± 4.3 years), low-load RT to failure (LLF, n = 11, 21 ± 1.3 years, three sets to failure at 25% of 1RM), high-load RT to failure (HLF, n = 11, 21 ± 1.4 years, three sets to failure at 75% of 1RM), and high-load RT without failure (HLNF, n = 11, 22 ± 1.5 years, six sets of five repetitions at 75% of 1RM) groups. Before and after the four weeks of training, 1RM, maximal voluntary isometric force, and corticospinal excitability (CSE) were measured. 1RM in the trained (20%, d = 0.70, 15%, d = 0.61) and the untrained knee extensors (5%, d = 0.27, 6%, d = 0.26) increased only in the HLF and HLNF groups, respectively. MVIC force increased only in the trained leg of the HLF (5%, d = 0.35) and HLNF groups (12%, d = 0.67). CSE decreased in the VL of both legs in the HLNF group (-19%, d = 0.44) and no changes occurred in the RF. In conclusion, high- but not low-load RT improves maximal voluntary force in the trained and the untrained knee extensors and fatigue did not further enhance these adaptations. Voluntary force improvements were unrelated to CSE changes in both legs.
