Effects of saddle height on economy in cycling

Research has demonstrated that properly adjusting saddle height is important for both performance and injury prevention during cycling. Peer-reviewed literature recommends the use of a 25 degrees to 35 degrees knee angle for injury prevention and 109% of inseam for optimal performance. Previous research has established that these 2 methods do not produce similar saddle heights. Previous research has also compared anaerobic power among a 25 degrees knee angle, a 35 degrees knee angle, and 109% of inseam and found an increase in anaerobic power at a 25 degrees knee angle. While anaerobic power production has been compared between these 2 methods, aerobic power and economy have not been. The purpose of this study was to determine the difference in economy between these 2 methods of adjusting saddle height. Fifteen subjects, consisting of 5 cyclists (all men) and 10 noncyclists (2 men and 8 women), participated in this study. A graded exercise protocol was utilized in order to determine intensity for the remaining trials. On the last 3 trials, subjects rode for 15 minutes at the resistance at which they reached 70% of Vo2max on a cycle ergometer. Vo2, heart rate (HR), and rating of perceived exertion (RPE) were compared to detect differences in economy between saddle heights. No significant differences were noted in HR or RPE. Vo2 was found to be significantly lower at a saddle height set with a 25 degrees knee angle when compared to a 35 degrees knee angle and 109% of inseam. Findings from this study support the use of a 25 degrees knee angle for both performance and injury prevention.     

Influence of saddle height on lower limb kinematics in well-trained cyclists: static vs. Dynamic evaluation in bike fitting

ABSTRACT: Ferrer-Roca, V, Roig, A, Galilea, P, and García-López, J. Influence of saddle height on lower limb kinematics in well-trained cyclists: Static vs. dynamic evaluation in bike fitting. J Strength Cond Res 26(11): 3025-3029, 2012-In cycling, proper saddle height is important because it contributes to the mechanical work of the lower limb joints, thus altering pedaling efficiency. The appropriate method to select optimal saddle height is still unknown. This study was conducted to compare a static (anthropometric measurements) vs. a dynamic method (2D analysis) to adjust saddle height. Therefore, an examination of the relationship between saddle height, anthropometrics, pedaling angles, and hamstring flexibility was carried out. Saddle height outside of the recommended range (106-109% of inseam length) was observed in 56.5% of the subjects. Inappropriate knee flexion angles using the dynamic method were observed in 26% of subjects. The results of this study support the concept that adjusting saddle height to 106-109% of inseam length may not ensure an optimal knee flexion (30-40°). To solve these discrepancies, we applied a multiple linear regression to study the relationship between anthropometrics, pedaling angles, and saddle height. The results support the contention that saddle height, inseam length, and knee angle are highly related (R = 0.963, p < 0.001). We propose a novel equation that relates these factors to recommend an optimal saddle height (108.6-110.4% of inseam length).     

A kinematic comparison of alterations to knee and ankle angles from resting measures to active pedaling during a graded exercise protocol

ABSTRACT: Peveler, WW, Shew, B, Johnson, S, and Palmer, TG. A kinematic comparison of alterations to knee and ankle angles from resting measures to active pedaling during a graded exercise protocol. J Strength Cond Res 26(11): 3004-3009, 2012-Saddle height is one of the most researched areas of bike fit. The current accepted method for adjusting saddle height involves the use of a goniometer to adjust saddle height so that a knee angle between 25° and 35° is obtained. This measurement is taken while the cyclist maintains a static position with the pedal at the 6-o'-clock position. However, the act of pedaling is dynamic, and angles may alter during movement. The purpose of this study was to examine the alterations to knee and ankle angle occurring from static measures to active pedaling across intensities experienced by cyclists during a graded exercise protocol. Thirty-four recreational to highly trained cyclists were evaluated using 2D analysis of stationary position and 3 active levels (level 1, respiratory exchange ratio of 1.00, and max). Dependent measures were compared using repeated measures analysis of variance (p = 0.05). When examining the results, it is evident that significant alterations to pedal stroke occur from stationary measures to active pedaling and as intensity increases toward maximal. Plantar flexion increased when moving from stationary measures to active pedaling, which resulted in an increase in knee angle. Although still greater than stationary measures, less plantar flexion occurred at higher intensities when compared with lower intensity cycling. Less plantar flexion at higher intensities is most likely a result of application of a larger downward torque occurring because of greater power requirements at higher intensities. There appeared to be greater variability in angle when examining novice cyclists in relation to more experienced cyclists. Although stationary measures are where a bike fit session will begin, observation during the pedal cycle may be needed to fine-tune the riders' fit.     

The effect of saddle position on maximal power output and moment generating capacity of lower limb muscles during isokinetic cycling

Saddle position affects mechanical variables during submaximal cycling, but little is known about its effect on mechanical performance during maximal cycling. Therefore, this study relates saddle position to experimentally obtained maximal power output and theoretically calculated moment generating capacity of hip, knee and ankle muscles during isokinetic cycling. Ten subjects performed maximal cycling efforts (5 s at 100 rpm) at different saddle positions varying ± 2 cm around the in literature suggested optimal saddle position (109% of inner leg length), during which crank torque and maximal power output were determined. In a subgroup of 5 subjects, lower limb kinematics were additionally recorded during submaximal cycling at the different saddle positions. A decrease in maximal power output was found for lower saddle positions. Recorded changes in knee kinematics resulted in a decrease in moment generating capacity of biceps femoris, rectus femoris and vastus intermedius at the knee. No differences in muscle moment generating capacity were found at hip and ankle. Based on these results we conclude that lower saddle positions are less optimal to generate maximal power output, as it mainly affects knee joint kinematics, compromising mechanical performance of major muscle groups acting at the knee.     

Muscular strength and jumping performance relationships in young women athletes

The relationships between muscular strength and vertical jumping performance were examined in young women (14-19 years) track and field jumpers (n = 20) and volleyball players (n = 21). The knee extensor muscular strength measured at 9 knee angles was correlated with jumping height and peak power at the squat (SJ) and the countermovement (CMJ) vertical jump tests. Pearson product coefficient of correlation was used to test the significance of these relationships (p 0.80). Specifically, in the volleyball players, the strong relationships were noted for muscular strength at the knee angle range of 40 degrees to 90 degrees and CMJ jumping height as well as SJ peak power. Results indicate the dissimilarity in the relationships between the knee extensor muscular strength and jumping performance in the young female track and field jumpers and volleyball players. In addition, it appears that the measure selected to evaluate jumping performance alters the correlational results.     

Effects on the crank torque profile when changing pedalling cadence in level ground and uphill road cycling

Despite the importance of uphill cycling performance during cycling competitions, there is very little research investigating uphill cycling, particularly concerning field studies. The lack of research is partly due to the difficulties in obtaining data in the field. The aim of this study was to analyse the crank torque in road cycling on level and uphill using different pedalling cadences in the seated position. Seven male cyclists performed four tests in the seated position (1) on level ground at 80 and 100 rpm, and (2) on uphill road cycling (9.25% grade) at 60 and 80 rpm.The cyclists exercised for 1 min at their maximal aerobic power. The bicycle was equipped with the SRM Training System (Schoberer, Germany) for the measurement of power output (W), torque (Nm), pedalling cadence (rpm), and cycling velocity (km h(-1)). The most important finding of this study indicated that at maximal aerobic power the crank torque profile (relationship between torque and crank angle) varied substantially according to the pedalling cadence and with a minor effect according to the terrain. At the same power output and pedalling cadence (80 rpm) the torque at a 45 degrees crank angle tended (p < 0.06) to be higher (+26%) during uphill cycling compared to level cycling. During uphill cycling at 60 rpm the peak torque was increased by 42% compared with level ground cycling at 100 rpm.When the pedalling cadence was modified, most of the variations in the crank torque profile were localised in the power output sector (45 degrees to 135 degrees).     

Influence of hip orientation on Wingate power output and cycling technique

The effect of altered hip orientation angle ([HOA] angle of hip joint center to bottom bracket relative to horizontal) on Wingate anaerobic test results and cycling technique while maintaining a constant body configuration angle (included angle between torso, hip, and bottom bracket) and maximum hip-to-pedal distance was examined. Nineteen recreational cyclists, all men, with no recent recumbent cycling experience completed 30-second Wingate tests in 3 recumbent positions (HOA = -20 degrees, -10 degrees, and 0 degrees ) and the standard cycling position (SCP) (HOA = 75 degrees ). Peak, average, and minimum power output, as well as fatigue index, were not significantly different across all positions (p < 0.01). Average hip and knee extension angles increased slightly, and ankle angle did not change as HOA increased. These findings indicate that although HOA does have a small effect on cycling kinematics, these effects are not large enough to alter short-term power output. Therefore, anaerobic power output may be evaluated and compared in the recumbent positions and the SCP.     

Relationship between cycling mechanics and core stability

Core stability has received considerable attention with regards to functional training in sports. Core stability provides the foundation from which power is generated in cycling. No research has described the relationship between core stability and cycling mechanics of the lower extremity. The purpose of this study was to determine the relationship between cycling mechanics and core stability. Hip, knee, and ankle joint kinematic and pedal force data were collected on 15 competitive cyclists while cycling untethered on a high-speed treadmill. The exhaustive cycling protocol consisted of cycling at 25.8 km x h(-1) while the grade was increased 1% every 3 minutes. A core fatigue workout was performed before the second treadmill test. Total frontal plane knee motion (test 1: 15.1 +/- 6.0 degrees ; test 2: 23.3 +/- 12.5 degrees), sagittal plane knee motion (test 1: 69.9 +/- 4.9 degrees ; test 2: 79.3 +/- 10.1 degrees), and sagittal plane ankle motion (test 1: 29.0 +/- 8.5 degrees ; test 2: 43.0 +/- 22.9 degrees) increased after the core fatigue protocol. No significant differences were demonstrated for pedaling forces. Core fatigue resulted in altered cycling mechanics that might increase the risk of injury because the knee joint is potentially exposed to greater stress. Improved core stability and endurance could promote greater alignment of the lower extremity when riding for extended durations as the core is more resistant to fatigue.     

Knee moments during run-to-cut maneuvers are associated with lateral trunk positioning

Non-contact anterior cruciate ligament (ACL) injuries account for approximately 70% of ACL ruptures and often occur during a sudden change in direction or pivot. Decreased neuromuscular control of the trunk in a controlled perturbation task has previously been associated with ACL injury incidence, while knee abduction moments and tibial internal rotation moments have been associated with ACL strain and ACL injury incidence. In this study, the association between movement of the trunk during a run-to-cut maneuver and loading of the knee during the same activity was investigated. External knee moments and trunk angles were quantified during a run-to-cut maneuver for 29 individuals. The trunk angles examined were outside tilt (frontal plane angle of the torso from vertical), angle between the ground reaction force (GRF) and the torso in the plane containing the GRF and shoulders (torso-GRF_shoulders); and angle between GRF and torso in the plane containing the GRF and pelvis (torso-GRF_pelvis). Significant positive associations were found between torso angles and peak knee abduction moments (outside tilt, p=0.002; and torso-GRF_shoulders, p=0.036) while a significant negative association was found between peak tibial internal rotation moment and outside tilt (p=0.021). Because the peaks of these moments occur at different times and minimal axial rotation moment is observed at peak knee abduction moment (-0.29±0.46%BW*ht), the positive association between peak knee abduction moment and torso lean suggests that increasing torso lean may increase ACL load and risk of injury.     

Kinematic analysis of hip and knee angles during landing after imagery in female athletes

ABSTRACT: Sarafrazi, S, Bt Abdulah, RT, and Amiri-Khorasani, M. Kinematics analysis of hip and knee angles during landing after imagery in female athletes. J Strength Cond Res 26(9): 2356-2363, 2012-In sport settings, imagery is regarded as one of the most popular and effective techniques to enhance the learning strategies and performance of skills. However, its effect on the correction of improper technique such as landing, which causes injury, is not clear. Therefore, the purpose of this study is to investigate the effect of imagery on knee and hip flexion angle during jump landing in women. The landing motions were captured from 40 female physical education students (height: 166.05 ± 7.52 cm; mass: 55.75 ± 9.23 kg; age: 20.45 ± 1.66 years) using a 3-dimensional technique at 60 Hz by 3 video cameras. There was a significant difference between no imagery (27.04 ± 2.40°) and imagery (22.98 ± 1.95°) on knee valgus angle, and also, there was a significant difference between no imagery (44.88 ± 13.46°) and imagery (62.35 ± 8.34°) on the knee flexion angle (p ≤ 0.001). There is, in addition, a significant difference between the effect of no imagery (28.60 ± 4.88°) and imagery (39.73 ± 7.29°) on hip flexion angle (p ≤ 0.001). It seems that imagery can be used to correct motions and movements. Based on this finding, we concluded that imagery, probably, can be used as a training strategy to change athletic motion; however, the authors suggest further investigation into the efficacy of imagery in the prevention of anterior cruciate ligament injury.     

Adjusted saddle position counteracts the modified muscle activation patterns during uphill cycling

The main aim of this project was to study muscle activity patterns during steep uphill cycling (UC) (i.e., with a gradient of 20%) with (1) normal saddle geometry and (2) with adjusted saddle position ASP (i.e., moving the saddle forward and changing the tilt of the saddle by 20%). Based on our preliminary case study, we hypothesized that: (1) during 20% UC muscle activity patterns would be different from those of level cycling (LC) and (2) during 20% UC with ASP muscle activity patterns would resemble those of LC. Twelve trained male cyclists were tested on an electromagnetically braked cycle ergometer under three conditions with the same work rate (80% of maximal power output) and cadence (90 rpm): level (LC), 20% UC and 20% UC with ASP. Electromyographic signals were acquired from m. tibialis anterior (TA), m. soleus (SO), m. gastrocnemius (GC), m. vastus lateralis (VL), m. vastus medialis (VM), m. rectus femoris (RF), m. biceps femoris (BF) and m. gluteus maximus (GM). Compared to LC, 20% UC significantly modified both the timing and the intensity of activity of the selected muscles, while muscles that cross the hip joint were the most affected (RF later onset, earlier offset, shorter range of activity and decrease in peak amplitude of 34%; BF longer range of activity; GM increase in peak amplitude of 44%). These changes in EMG patterns during 20% UC were successfully counteracted by the use of ASP and it was interesting to observe that the use of ASP during 20% UC was perceived positively by all cyclists regarding both comfort and performance. These results could have a practical relevance in terms of improving performance during UC, together with reducing discomfort.     

Correlation between trochlear groove depth and patellar position during open and closed kinetic chain exercises in subjects with anterior knee pain

The purpose of this study was to correlate the trochlear shape and patellar tilt angle and lateral patellar displacement at rest and maximal voluntary isometric contraction (MVIC) exercises during open (OKC) and closed kinetic chain (CKC) in subjects with and without anterior knee pain. Subjects were all women, 20 who were clinically healthy and 19 diagnosed with anterior knee pain. All subjects were evaluated and subjected to magnetic resonance exams during OKC and CKC exercise with the knee placed at 15, 30, and 45 degrees of flexion. The parameters evaluated were sulcus angle, patellar tilt angle and patellar displacement using bisect offset. Pearson's r coefficient was used, with p < .05. Our results revealed in knee pain group during CKC and OKC at 15 degrees that the increase in the sulcus angle is associated with a tilt increase and patellar lateral displacement. Comparing sulcus angle, patellar tilt angle and bisect offset values between MVIC in OKC and CKC in the knee pain group, it was observed that patellar tilt angle increased in OKC only with the knee flexed at 30 degrees. Based on our results, we conclude that reduced trochlear depth is correlated with increased lateral patellar tilt and displacement during OKC and CKC at 15 degrees of flexion in people with anterior knee pain. By contrast, 30 degrees of knee flexion in CKC is more recommended in rehabilitation protocols because the patella was more stable than in other positions.     

Influence of knee flexion angle and age on triceps surae muscle activity during heel raises

ABSTRACT: Hébert-Losier, K, Schneiders, AG, García, JA, Sullivan, SJ, and Simoneau, GG. Influence of knee flexion angle and age on triceps surae muscle activity during heel raises. J Strength Cond Res 26(11): 3124-3133, 2012-Triceps surae and Achilles tendon injuries are frequent in sports medicine, particularly in middle-aged adults. Muscle imbalances and weakness are suggested to be involved in the etiology of these conditions, with heel-raise testing often used to assess and treat triceps surae (TS) injuries. Although heel raises are recommended with the knee straight for gastrocnemius and bent for soleus (SOL), the extent of muscle selectivity in these positions is not clear. This study aimed to determine the influence of knee angle and age on TS muscle activity during heel raises. Forty-eight healthy men and women were recruited from a younger-aged (18-25 years) and middle-aged (35-45 years) population. All the subjects performed unilateral heel raises in 0° and 45° knee flexion (KF). Soleus, gastrocnemius medialis (GM) and gastrocnemius lateralis (GL) surface electromyography signals were processed to compute root-mean-square amplitudes, and data were analyzed using mixed-effects models and stepwise regression. The mean TS activity during heel raises was 23% of maximum voluntary isometric contraction when performed in 0° KF and 21% when in 45°. Amplitudes were significantly different between TS muscles (p < 0.001) and KF angles (p < 0.001), with a significant interaction (p < 0.001). However, the age of the population did not influence the results (p = 0.193). The findings demonstrate that SOL activity was 4% greater when tested in 45° compared with 0° KF and 5% lower in the GM and GL. The results are consistent with the recommended use of heel raises in select knee positions for assessing, training, and rehabilitating the SOL and gastrocnemius muscles; however, the 4-5% documented change in activity might not be enough to significantly influence clinical outcome measures or muscle-specific benefits. Contrary to expectations, TS activity did not distinguish between middle-aged and younger-aged adults, despite the higher injury prevalence in middle age.     

In vivo hip joint loads and pedal forces during ergometer cycling

The rising prevalence of osteoarthritis and an increase in total hip replacements calls for attention to potential therapeutic activities. Cycling is considered as a low impact exercise for the hip joint and hence recommended. However, there are limited data about hip joint loading to support this claim. The aim of this study was to measure synchronously the in vivo hip joint loads and pedal forces during cycling. The in vivo hip joint loads were measured in 5 patients with instrumented hip implants. Data were collected at several combinations of power and cadence, at two saddle heights.Joint loads and pedal forces showed strong linear correlation with power. So the relationship between the external pedal forces and internal joint forces was shown. While cycling at different cadences the minimum joint loads were acquired at 60 RPM. The lower saddle height configuration results in an approximately 15% increase compared to normal saddle height.The results offered new insights into the actual effects of cycling on the hip joint and can serve as useful tools while developing an optimum cycling regimen for individuals with coxarthrosis or following total hip arthroplasty. Due to the relatively low contact forces, cycling at a moderate power level of 90 W at a normal saddle height is suitable for patients.     

Non-driving intersegmental knee moments in cycling computed using a model that includes three-dimensional kinematics of the shank/foot and the effect of simplifying assumptions

Assessing the importance of non-driving intersegmental knee moments (i.e. varus/valgus and internal/external axial moments) on over-use knee injuries in cycling requires the use of a three-dimensional (3-D) model to compute these loads. The objectives of this study were: (1) to develop a complete, 3-D model of the lower limb to calculate the 3-D knee loads during pedaling for a sample of the competitive cycling population, and (2) to examine the effects of simplifying assumptions on the calculations of the non-driving knee moments. The non-driving knee moments were computed using a complete 3-D model that allowed three rotational degrees of freedom at the knee joint, included the 3-D inertial loads of the shank/foot, and computed knee loads in a shank-fixed coordinate system. All input data, which included the 3-D segment kinematics and the six pedal load components, were collected from the right limb of 15 competitive cyclists while pedaling at 225 W and 90 rpm. On average, the peak varus and internal axial moments of 7.8 and 1.5 N m respectively occurred during the power stroke whereas the peak valgus and external axial moments of 8.1 and 2.5 N m respectively occurred during the recovery stroke. However, the non-driving knee moments were highly variable between subjects; the coefficients of variability in the peak values ranged from 38.7% to 72.6%. When it was assumed that the inertial loads of the shank/foot for motion out of the sagittal plane were zero, the root-mean-squared difference (RMSD) in the non-driving knee moments relative to those for the complete model was 12% of the peak varus/valgus moment and 25% of the peak axial moment. When it was also assumed that the knee joint was revolute with the flexion/extension axis perpendicular to the sagittal plane, the RMSD increased to 24% of the peak varus/valgus moment and 204% of the peak axial moment. Thus, the 3-D orientation of the shank segment has a major affect on the computation of the non-driving knee moments, while the inertial contributions to these loads for motions out of the sagittal plane are less important.     

The effects of antagonist prefatigue on agonist torque and electromyography

This study assessed the effects of hamstring prefatigue on peak torque, peak power, time to peak torque, knee angle of peak torque, and electromyography (EMG) activity of the hamstrings and quadriceps group during knee extensions at angular velocities of 60 degrees, 180 degrees, and 300 degrees.s(-1). Twenty Division I wrestlers performed 5 maximal knee extensions in prefatigued and nonfatigued conditions of the hamstring group. This study demonstrated that when the hamstrings were prefatigued, the quadriceps produced significant decreases in peak torque of 1.7% (p < 0.05), peak power of 11% (p < 0.05), and rate to peak torque of 6.4% (p < 0.01) as compared with the nonfatigued state. When the hamstrings were prefatigued, they produced a 25% greater amount of EMG activity during knee extension (p < 0.01) than when not prefatigued. There was no significant difference in quadriceps EMG activity whether the hamstring group was prefatigued or not (p > 0.05). The decrease in quadriceps peak torque during the prefatigued condition was more pronounced (p < 0.01) at an angular velocity of 60 degrees.s(-1) than at 180 degrees or 300 degrees.s(-1). In other words, prefatiguing the antagonist appears to be most detrimental to torque output of the quadriceps in the condition that most closely replicates the speed at which "isotonic" weight training occurs (60 degrees.s(-1)) and suggests a limitation to agonist-antagonist superset training.     

Effects of Forefoot Shoe on Knee and Ankle Loading during Running in Male Recreational Runners

Objectives: Although overuse running injury risks for the ankle and knee are high, the effect of different shoe designs on Achilles tendon force (ATF) and Patellofemoral joint contact force (PTF) loading rates are unclear. Therefore, the primary objective of this study was to compare the ATF at the ankle and the PTF and Patellofemoral joint stress force (PP) at the knee using different running shoe designs (forefoot shoes vs. normal shoes). Methods: Fourteen healthy recreational male runners were recruited to run over a force plate under two shoe conditions (forefoot shoes vs. normal shoes). Sagittal plane ankle and knee kinematics and ground reaction forces were simultaneously recorded. Ankle joint mechanics (ankle joint angle, velocity, moment and power) and the ATF were calculated. Knee joint mechanics (knee joint angle velocity, moment and power) and the PTF and PP were also calculated. Results: No significant differences were observed in the PTF, ankle plantarflexion angle, ankle dorsiflexion power, peak vertical active force, contact time and PTF between the two shoe conditions. Compared to wearing normal shoes, wearing the forefoot shoes demonstrated that the ankle dorsiflexion angle, knee flexion velocity, ankle dorsiflexion moment extension, knee extension moment, knee extension power, knee flexion power and the peak patellofemoral contact stress were significantly reduced. However, the ankle dorsiflexion velocity, ankle plantarflexion velocity, ankle plantarflexion moment and Achilles tendons force increased significantly. Conclusions: These findings suggest that wearing forefoot shoes significantly decreases the patellofemoral joint stress by reducing the moment of knee extension, however the shoes increased the ankle plantarflexion moment and ATF force. The forefoot shoes effectively reduced the load on the patellofemoral joint during the stance phase of running. However, it is not recommended for new and novice runners and patients with Achilles tendon injuries to wear forefoot shoes.     

Movement variability cannot be determined reliably from no-marker conditions

We sought to quantify the proportion of total variability due to movement variability in digitizing marker and no-marker conditions in treadmill running. Manually digitized markers gave variabilities in joint angles within 0.4° of those from auto-tracking. Marker conditions allowed reliable estimation of movement variability by an experienced operator; the contribution of movement variability to total variability, expressed by omega-squared, had averages across the four operators of 97% for the knee angle and 93% for the hip. The no-marker condition did not allow reliable estimation of movement variability—the above figures fell, respectively, to 72% and 48%—and cannot be recommended. The group design in the marker condition produced omega-squared values of 97% knee and 91% hip, showing excellent objectivity (inter-operator reliability). However, without markers, these values fell to 47% and 15%, respectively, indicating that movement variability cannot be assessed objectively in no-marker conditions.     

Age differences in knee extension power, contractile velocity, and fatigability.

The purposes of this study were to examine age and gender differences in knee extensor strength, power, and fatigue using open- and closed-chain testing procedures. We tested the hypothesis that specific strength (strength/unit muscle mass) would not differ by age, whereas age differences in specific power and fatigue would remain consequent to blunted maximal contractile velocity. Skeletal muscle performance was examined in 28 young (26.9 +/- 0.7 yr) and 24 older (63.6 +/- 0.8 yr) men and women. Assessments included one-repetition maximum strength for knee extension, leg press, and squat; concentric knee extensor peak power, velocity, and fatigability; and sit-to-stand power, fatigability, and relative neural activation (electromyograph activity during sit-to-stand movement normalized to electromyograph activity during isometric maximum voluntary contraction). Thigh lean mass (TLM; kg) was assessed by dual-energy X-ray absorptiometry. Specific strength (N/kg TLM) and specific power (W/kg TLM) were estimated by dividing absolute values by TLM. Age differences in specific strength were observed for knee extension only (young, 41.2 +/- 1.0 N/kg TLM; older, 32.4 +/- 1.0 N/kg TLM; P < 0.05). Adjustment for TLM did not negate age differences in knee extension specific power (25-41% lower in older; P < 0.05) across loads tested. Older adults experienced fatigue across 10 repetitions of knee extension as peak velocity fell by 24% (P < 0.05). Deficits in concentric power persist after adjustment for TLM as maximum contractile velocity falls markedly with aging. Older adults are less capable of sustaining maximum concentric velocity during repetitive contractions. These findings suggest that velocity impairments are a possible contributor to mobility loss and falls risk among older adults. Interventions for improving contractile velocity should be pursued.     

The correlation of segment accelerations and impact forces with knee angle in jump landing

Impact forces and shock deceleration during jumping and running have been associated with various knee injury etiologies. This study investigates the influence of jump height and knee contact angle on peak ground reaction force and segment axial accelerations. Ground reaction force, segment axial acceleration, and knee angles were measured for 6 male subjects during vertical jumping. A simple spring-mass model is used to predict the landing stiffness at impact as a function of (1) jump height, (2) peak impact force, (3) peak tibial axial acceleration, (4) peak thigh axial acceleration, and (5) peak trunk axial acceleration. Using a nonlinear least square fit, a strong (r = 0.86) and significant (p < or = 0.05) correlation was found between knee contact angle and stiffness calculated using the peak impact force and jump height. The same model also showed that the correlation was strong (r = 0.81) and significant (p < or = 0.05) between knee contact angle and stiffness calculated from the peak trunk axial accelerations. The correlation was weaker for the peak thigh (r = 0.71) and tibial (r = 0.45) axial accelerations. Using the peak force but neglecting jump height in the model, produces significantly worse correlation (r = 0.58). It was concluded that knee contact angle significantly influences both peak ground reaction forces and segment accelerations. However, owing to the nonlinear relationship, peak forces and segment accelerations change more rapidly at smaller knee flexion angles (i.e., close to full extension) than at greater knee flexion angles.