Evaluation of hop performance in children with anterior cruciate ligament reconstruction using healthy reference data: A cross-sectional study.

BACKGROUND: Hop performance evaluation in children after anterior cruciate ligament (ACL) reconstruction may benefit from comparison to healthy controls. Thus, the purpose was to investigate the hop performance in children one year after ACL reconstruction with a comparison to healthy controls. METHODS: Hop performance data from children with ACL reconstruction one year post-surgery and healthy children were compared. Four one-legged hop test data were analyzed: 1) single hop (SH), 2) 6 m timed hop (6 m-timed), 3) triple hop (TH), and 4) cross-over hop (COH). Outcomes were the best result (longest/fastest hop) from each leg and limb asymmetry. Differences in hop performance between-limbs (operated versus non-operated) and between-groups were estimated. RESULTS: 98 children with ACL reconstruction and 290 healthy children were included. Few statistically significant group differences were observed. Girls with ACL reconstruction outperformed healthy controls in two tests on the operated leg SH, COH) and in three tests on the non-operated leg (SH, TH, COH). However, the girls performed 4-5% worse on the operated leg when compared to the non-operated leg in all hop tests. No statistically significant between-group differences in the limb asymmetry were found. CONCLUSION: The hop performance in children with ACL reconstruction one year post-surgery was largely comparable to the level of healthy controls. Despite this, we cannot exclude that neuromuscular deficits exist among the children with ACL reconstruction. The inclusion of a healthy control group for evaluating hop performance evoked complex findings regarding the ACL reconstructed girls. Thus, they may represent a selected group.

Day-to-Day Reliability of Nonlinear Methods to Assess Walking Dynamics.

The present study investigated the day-to-day reliability (quantified by the absolute and relative reliability) of nonlinear methods used to assess human locomotion dynamics. Twenty-four participants of whom twelve were diagnosed with knee osteoarthritis completed 5 min of treadmill walking at self-selected preferred speed on two separate days. Lower limb kinematics were recorded at 100 Hz and hip, knee, and ankle joint angles, three-dimensional (3D) sacrum marker displacement and stride time intervals were extracted for 170 consecutive strides. The largest Lyapunov exponent and correlation dimension were calculated for the joint angle and sacrum displacement data using three different state space reconstruction methods (group average, test-retest average, individual time delay and embedding dimension). Sample entropy and detrended fluctuation analysis (DFA) were applied to the stride time interval time series. Relative reliability was assessed using intraclass correlation coefficients and absolute reliability was determined using measurement error (ME). For both joint angles and sacrum displacement, there was a general pattern that the group average state space reconstruction method provided the highest relative reliability and lowest ME compared to the individual and test-retest average methods. The DFA exhibited good reliability, while the sample entropy showed poor reliability. The results comprise a reference material that can inspire and guide future studies of nonlinear gait dynamics.

Economy, Movement Dynamics, and Muscle Activity of Human Walking at Different Speeds.

The complex behaviour of human walking with respect to movement variability, economy and muscle activity is speed dependent. It is well known that a U-shaped relationship between walking speed and economy exists. However, it is an open question if the movement dynamics of joint angles and centre of mass and muscle activation strategy also exhibit a U-shaped relationship with walking speed. We investigated the dynamics of joint angle trajectories and the centre of mass accelerations at five different speeds ranging from 20 to 180% of the predicted preferred speed (based on Froude speed) in twelve healthy males. The muscle activation strategy and walking economy were also assessed. The movement dynamics was investigated using a combination of the largest Lyapunov exponent and correlation dimension. We observed an intermediate stage of the movement dynamics of the knee joint angle and the anterior-posterior and mediolateral centre of mass accelerations which coincided with the most energy-efficient walking speed. Furthermore, the dynamics of the joint angle trajectories and the muscle activation strategy was closely linked to the functional role and biomechanical constraints of the joints.

Intra-subject variability in muscle activity and co-contraction during jumps and landings in children and adults.

We investigated muscle activity, intra-subject variability in muscle activity and co-contraction during vertical jumps and landings in children and adults. Ten male children and 10 male adults completed 10 countermovement jumps (CMJ), 10 drop jumps (DJ) from 30 cm, 10 low and high landings from 30 and 60 cm for the children and 60 and 90 cm for the adults. The adults also performed ten DJ from 60 cm. EMG was recorded from nine lower limb muscles in the right leg and normalized to isometric MVC. Statistical parametric mapping was used to reveal differences in the muscle activity and intra-subject variability in the muscle activity. Co-contraction was quantified for two thigh muscle pairs and one plantar flexor/dorsiflexor muscle pair and group differences were assessed (two-way ANOVA). No significant differences were observed in the less eccentric demanding CMJ while significantly higher muscle activity magnitude and intra-subject variability were observed for the children during the initial part of the contact phase of DJ and landings, indicating a less consistent muscle activity pattern in the children. This may indicate that vertical jumps/landings involving a high amount of eccentric muscle contraction constrain the muscle activation in children, possibly because of immature motor control.

Dynamic balance during gait in children and adults with Generalized Joint Hypermobility.

BACKGROUND: The purpose of the study was to investigate if differences of the head and trunk stability and stabilization strategies exist between subjects classified with Generalized Joint Hypermobility and healthy controls during gait. It was hypothesized that joint hypermobility could lead to decreased head and trunk stability and a head stabilization strategy similar to what have been observed in individuals with decreased locomotor performance. METHODS: A comparative study design was used wherein 19 hypermobile children were compared to 19 control children, and 18 hypermobile adults were compared to 18 control adults. The subjects were tested during normal walking and walking on a line. Kinematics of head, shoulder, spine and pelvis rotations were measured by five digital video cameras in order to assess the segmental stability (angular dispersion) and stabilization strategies (anchoring index) in two rotational components: roll and yaw. FINDINGS: Hypermobile children and adults showed decreased lateral trunk stability in both walking conditions. In hypermobile children, it was accompanied with decreased head stability as the head was stabilized by the inferior segment when walking on a line. Several additional differences were observed in stability and stabilization strategies for both children and adults. INTERPRETATION: Stability of the trunk was decreased in hypermobile children and adults. This may be a consequence of decreased stability of the head. Hypermobile children showed a different mode of head stabilization during more demanding locomotor conditions indicating delayed locomotor development. The findings reflect that Generalized Joint Hypermobility probably include motor control deficits.

Slide-based ergometer rowing: effects on force production and neuromuscular activity.

Force production profile and neuromuscular activity during slide-based and stationary ergometer rowing at standardized submaximal power output were compared in 14 male and 8 female National Team rowers. Surface electromyography (EMG) was obtained in selected thoracic and leg muscles along with synchronous measurement of handle force and rate of force development (RFD). Compared to stationary conditions, slide-based peak force decreased by 76 (57-95) N (mean 95% CI) in males (P < 0.001) and 20 (8-31) N (P < 0.05) in females. Stroke rate increased (+10.7%) and late-phase RFD decreased (-20.7%) in males (P < 0.05). Neuromuscular activity in m. vastus lateralis decreased in the initial drive phase from 59% to 51% of EMG max in males and from 57% to 52% in females (P < 0.01-0.05), while also decreasing in the late recovery phase from 20% to 7% in males and 17% to 7% in females (P < 0.01). Peak force and maximal neuromuscular activity in the shoulder retractors always occurred in the second quartile of the drive phase. In conclusion, peak force and late-phase RFD (males) decreased and stroke rate increased (males) during slide-based compared to stationary ergometer rowing, potentially reducing the risk of overuse injury. Neuromuscular activity was more affected in leg muscles than thoracic muscles by slide-based ergometer rowing.

Effects of an intensive weight loss program on knee joint loading in obese adults with knee osteoarthritis.

OBJECTIVE: To determine the effect of an intensive weight loss program on knee joint loads during walking in obese patients with knee osteoarthritis (OA). METHODS: Participants included 157 obese knee OA patients that underwent a 16-week dietary intervention. Three-dimensional gait analyses were performed before and after the intervention at the participants' freely chosen walking speed. Knee joint compression forces, axial impulses, knee flexion angle and frontal and sagittal plane knee moments were calculated to determine the biomechanical effects of the weight loss. RESULTS: 157 subjects (89% of the initial cohort) completed the 16-week intervention. The average weight loss of 13.7 kg (P<.0001) corresponded to 13.5% of the baseline body weight. The weight loss resulted in a 7% reduction in knee joint loading, a 13% lower axial impulse, and a 12% reduction in the internal knee abductor moment (KAM). There were no clear effects on sagittal plane knee moments or peak knee flexion angle. Linear regression analyses adjusted for changes in walking speed showed that for every 1 kg in weight loss, the peak knee load was reduced by 2.2 kg. Thus, every kilo reduction in body weight was related to more than twice the reduction in peak knee force at a given walking speed. CONCLUSION: Weight loss is an excellent short-term investment in terms of joint loading for patients with combined obesity and knee OA. The effects of sustained weight loss on disease progression and symptoms in relation to biomechanical factors remain to be shown.

Acute fatigue impairs neuromuscular activity of anterior cruciate ligament-agonist muscles in female team handball players.

In sports, like team handball, fatigue has been associated with an increased risk of anterior cruciate ligament (ACL) injury. While effects of fatigue on muscle function are commonly assessed during maximal isometric voluntary contraction (MVC), such measurements may not relate to the muscle function during match play. The purpose of this study was to investigate the effect of muscle fatigue induced by a simulated handball match on neuromuscular strategy during a functional sidecutting movement, associated with the incidence of ACL injury. Fourteen female team handball players were tested for neuromuscular activity [electromyography (EMG)] during a sidecutting maneuver on a force plate, pre and post a simulated handball match. MVC was obtained during maximal isometric quadriceps and hamstring contraction. The simulated handball match consisted of exercises mimicking handball match activity. Whereas the simulated handball match induced a decrease in MVC strength for both the quadriceps and hamstring muscles (P<0.05), a selective decrease in hamstring neuromuscular activity was seen during sidecutting (P<0.05). This study shows impaired ACL-agonist muscle (i.e. hamstring) activity during sidecutting in response to acute fatigue induced by handball match play. Thus, screening procedures should involve functional movements to reveal specific fatigue-induced deficits in ACL-agonist muscle activation during high-risk phases of match play.

Is it possible to reduce the knee joint compression force during level walking with hiking poles?

Walking with hiking poles has become a popular way of exercising. Walking with poles is advocated as a physical activity that significantly reduces the loading of the hip, knee and ankle joints. We have previously observed that pole walking does not lead to a reduction of the load on the knee joint. However, it is unclear whether an increased force transmitted through the poles can reduce the load on the knee joint. Thus, the purpose of the present study was to investigate if an increased load transmitted through the arms to the poles could reduce the knee joint compression force during level walking with poles. We hypothesized that an increased pole force would result in a reduction of the knee joint compression force. Gait analyses from 10 healthy subjects walking with poles were obtained. The pole force was measured simultaneously during the gait analyses. The knee joint compression forces were estimated by using a biomechanical knee joint model. The results showed that the subjects were able to increase the pole force by 2.4 times the normal pole force. However, this did not lead to a reduction in the knee joint compressive force and we rejected our hypothesis. In conclusion, the use of poles during level walking does not seem to reduce knee joint compressive loads. However, it is possible that the use of poles in other populations (e.g. osteoarthritis patients) and in terrain would unload the knee joint. This should be investigated in the future.

Experimental muscle pain during a forward lunge--the effects on knee joint dynamics and electromyographic activity.

OBJECTIVE: The purpose of this study was to investigate whether the knee joint dynamics during a forward lunge could be modulated by experimentally induced vastus medialis pain in healthy subjects. DESIGN: Randomised cross-over study. SETTING: Biomechanical movement laboratory. PARTICIPANTS: 20 healthy subjects were included. One subject was excluded during data collection. INTERVENTION: The subjects performed forward lunges before, during and 20 minutes after induction of experimental quadriceps muscle pain. Muscle pain was induced using hypertonic saline (5.8%) injected intramuscularly. Isotonic saline (0.9%) was used as control. MAIN OUTCOME MEASUREMENTS: Three-dimensional movement analyses were performed and inverse dynamics were used to calculate joint kinematics and kinetics for ankle, knee and hip joints. Electromyographic (EMG) signals of the hamstrings and quadriceps muscles were recorded. RESULTS: During and after pain, significant decreases in knee joint dynamics and EMG recordings were observed. CONCLUSION: The study shows that local pain in the quadriceps is capable of modulating movements with high knee joint dynamics. The results may have implications in the management of muscle pain and prevention of injuries during activities involving the knee joint.

Nordic Walking does not reduce the loading of the knee joint.

The use of Nordic Walking (NW) as a rehabilitation modality has increased considerably. NW (walking with poles) is advocated as a healthy physical activity that reduces the load on the knees. Few studies using the techniques of NW exist, and the findings are contradictory. The aim of this study was to investigate whether NW reduces the loadings upon the knee joint compared with walking without poles (NP). Seven experienced female NW instructors volunteered. Three-dimensional gait analyses were performed. Internal flexor and extensor joint moments were calculated using an inverse dynamics approach and the knee joint compressive forces were calculated. No differences in compression or shear forces between NW and NP were found. The peak knee flexion angles were larger during NW (-32.5+/-6.0 degrees) compared with NP (-28.2+/-4.2 degrees). The hip range of motion (ROM) was significantly increased during NW (64.4+/-10.2 degrees) compared with NP (57.8+/-9.7 degrees); no differences in the knee and ankle joint ROM were observed. The changes in the joint angles were not followed by changes in the joint dynamics. The present study does not support the statement that NW reduces the load on the knees.

Exercise-induced rib stress fractures: potential risk factors related to thoracic muscle co-contraction and movement pattern.

The etiology of exercise-induced rib stress fractures (RSFs) in elite rowers is unclear. The purpose of the study was to investigate thoracic muscle activity, movement patterns and muscle strength in elite rowers. Electromyographic (EMG) and 2-D video analysis were performed during ergometer rowing, and isokinetic muscle strength was measured in seven national team rowers with a history of RSF and seven matched controls (C). RSF displayed a higher velocity of the seat in the initial drive phase (RSF: 0.25+/-0.03, 0.25 (0.15-0.33) m/s vs C: 0.15+/-0.06, 0.18 (-0.11-0.29) m/s P=0.028) (Mean+/-SEM, median and range). Further, RSF had greater co-contraction of m. serratus anterior and m. trapezius in the mid-drive phase (RSF: 47.5+/-3.4, 48.5 (35.8-60.2)% EMG signal overlap vs C: 30.8+/-6.5, 27.0 (11.2-61.6)%P=0.043). In addition, the RSF subjects showed a lower knee-extension to elbow-flexion strength ratio (RSF: 4.2+/-0.22, 4.3 (3.5-5.1) vs C: 4.8+/-0.16, 5.0 (4.2-5.3) P=0.043), indicating stronger arms relative to legs compared with controls. In conclusion, increased thoracic muscle co-contraction, altered movement patterns and reduced leg/arm strength ratio were observed in the RSF subjects, which may all predispose toward an increased risk of RSF.

Region-specific mechanical properties of the human patella tendon.

The present study investigated the mechanical properties of tendon fascicles from the anterior and posterior human patellar tendon. Collagen fascicles from the anterior and posterior human patellar tendon in healthy young men (mean +/- SD, 29.0 +/- 4.6 yr, n = 6) were tested in a mechanical rig. A stereoscopic microscope equipped with a digital camera recorded elongation. The fascicles were preconditioned five cycles before the failure test based on pilot data on rat tendon fascicle. Human fascicle length increased with repeated cycles (P < 0.05); cycle 5 differed from cycle 1 (P < 0.05), but not cycles 2-4. Peak stress and yield stress were greater for anterior (76.0 +/- 9.5 and 56.6 +/- 10.4 MPa, respectively) than posterior fascicles (38.5 +/- 3.9 and 31.6 +/- 2.9 MPa, respectively), P < 0.05, while yield strain was similar (anterior 6.8 +/- 1.0%, posterior 8.7 +/- 1.4%). Tangent modulus was greater for the anterior (1,231 +/- 188 MPa) than the posterior (583 +/- 122 MPa) fascicles, P < 0.05. In conclusion, tendon fascicles from the anterior portion of the human patellar tendon in young men displayed considerably greater peak and yield stress and tangent modulus compared with the posterior portion of the tendon, indicating region-specific material properties.

Comparison of inverse dynamics calculated by two- and three-dimensional models during walking.

The purpose of the study was to compare joint moments calculated by a two- (2D) and a three-dimensional (3D) inverse dynamics model to examine how the different approaches influenced the joint moment profiles. Fifteen healthy male subjects participated in the study. A five-camera video system recorded the subjects as they walked across two force plates. The subjects were invited to approach a walking speed of 4.5 km/h. The ankle, knee and hip joint moments in the sagittal plane were calculated by 2D and 3D inverse dynamics analysis and compared. Despite the uniform walking speed (4.53 km/h) and similar footwear, relatively large inter-individual variations were found in the joint moment patterns during the stance phase. The differences between individuals were present in both the 2D and 3D analysis. For the entire sample of subjects the overall time course pattern of the ankle, knee and hip joint moments was almost identical in 2D and 3D. However, statistically significant differences were observed in the magnitude of the moments, which could be explained by differences in the joint centre location and joint axes used in the two approaches. In conclusion, there were differences between the magnitude of the joint moments calculated by 2D and 3D inverse dynamics but the inter-individual variation was not affected by the different models. The simpler 2D model seems therefore appropriate for human gait analysis. However, comparisons of gait data from different studies are problematic if the calculations are based on different approaches. A future perspective for solving this problem could be to introduce a standard proposal for human gait analysis.

Evaluation of the walking pattern in clubfoot patients who received early intensive treatment.

The walking pattern in a group of nine adult male subjects who had received early intensive treatment for congenital clubfoot was evaluated and compared to the walking pattern in a control group of 15 adult healthy male subjects. All subjects were filmed with a five-camera video system as they walked across two force plates. A three-dimensional inverse dynamics approach was used to calculate average joint angles, moments, power, and work. The results showed that there were no differences in the joint angles between the two groups. The overall patterns of the joint moments were very similar in the two groups. However, analysis revealed a smaller ankle joint moment and larger knee and hip joint moments in those with clubfoot. It was concluded that the larger knee and hip joint moments served as compensation for the smaller ankle moment. The reduced ankle moment and work developed about the ankle joint in the clubfeet could possibly be owing to weaker plantar flexors. In conclusion, gait analysis can be an important tool when evaluating treatment for clubfoot. However, further investigation is needed to determine whether the higher hip and knee joint moments observed in subjects with clubfoot may lead to the development of knee or hip joint pathologies.

Choice of jumping strategy in two standard jumps, squat and countermovement jump--effect of training background or inherited preference?

Six male subjects, three professional ballet dancers and three elite volleyball players, performed maximal vertical jumps from 1) a static preparatory position (squat jump), 2) starting with a countermovement (countermovement jump) and 3) a specific jump for ballet and for volleyball, respectively. The jumps were recorded on highspeed film (500 Hz) combined with registration of ground reaction forces, and net joint moments were calculated by inverse dynamics. The purpose was to investigate the choice of strategy in two standard jumps, squat jump and countermovement jump. The volleyball jump was performed with a sequential strategy and the ballet jump was performed with a simultaneous strategy. In the two standard jumps, the choice of strategy was individual and not related to training background. This was additionally confirmed in a test of seven ballet dancers and seven volleyball players.