Shock absorption characteristics of running shoes

The change in shock absorption properties of running shoes was evaluated as a function of miles run. Different models of running shoes encompassing a wide range in retail price were obtained and mechanically tested to simulate the repeated heel strikes of running. The energy absorbed by the shoes was determined from the area under the load deformation curve at the equivalent of 0, 5, 10, 25, 50, 75, 100, 125, 150, 200, 250, 300, and 500 miles of running. Shoes were also tested at similar intervals after having been worn by volunteers during normal training. An approximate 33% difference in the initial shock absorption was observed in the different shoe models. In general, the shoes retained approximately 75% of their initial shock absorption capability after 50 miles of simulated running, and approximately 67% after 100 to 150 miles. Between 250 and 500 miles the shoes retained less than 60% of their initial shock absorption capacity. No differences in shock absorption characteristics were apparent based upon either shoe price or the manufacturer model. The results of shoes tested by the volunteer runners also showed a marked reduction in shock absorption with mileage. The loss, however, was not as great as in the machine-simulated running, with approximately 70% of initial shock absorption retained at 500 miles.     

Biomechanics of running with rocker shoes

Objectives

Load reduction is an important consideration in conservative management of tendon overuse injuries such as Achilles tendinopathy. Previous research has shown that the use of rocker shoes can reduce the positive ankle power and plantar flexion moment which might help in unloading the Achilles tendon. Despite this promising implication of rocker shoes, the effects on hip and knee biomechanics remain unclear. Moreover, the effect of wearing rocker shoes on different running strike types is unexplored. The aim of this study was to investigate biomechanics of the ankle, knee and hip joints and the role of strike type on these outcomes.

The effect of heel-to-toe drop of running shoes on patellofemoral joint stress during running

BackgroundTraditional running shoes with heel-to-toe drops is thought to be a contributor to increased patellofemoral joint stress, which is proposed as a mechanism of patellofemoral pain.Research questionIs there an increase in patellofemoral joint stress when running in shoes with drops compared to running in shoes without a drop?MethodsLower limbs kinematics and ground reaction force were collected from eighteen healthy runners during over-ground running in shoes with 15 mm, 10 mm, 5 mm drops, and without a drop. Patellofemoral joint force and stress were calculated from the kinematic and kinetic data using a biomechanical model of the patellofemoral joint.ResultsThe peak patellofemoral joint stress was increased by more than 15% when running in shoes with 15 mm and 10 mm drops compared to running in shoes without a drop (p = 0.003, p = 0.001). The knee flexion angle was significantly increased when running in shoes with 15 mm, 10 mm and 5 mm drops (p = 0.014, p = 0.003, p = 0.002), the knee extension moment (p = 0.009, p = 0.002) and patellofemoral joint force (p = 0.003, p = 0.001) were increased when running in shoes with 15 mm and 10 mm drops, compared to running in shoes without a drop.SignificanceCompared to running in shoes without a drop, running in shoes with drops > 5 mm increase the peak patellofemoral joint stress significantly, which is mainly due to the increased knee extension moment.     

The effects of shoes on the torsion and rearfoot motion in running.

Excessive pronation is accepted as a good indicator for various running injuries. The least amount of pronation takes place when running barefoot. The latest investigations show that this is connected to a large torsional movement between forefoot and rearfoot which can be influenced by the shoe sole construction. The shoes which are in use among runners in track and field are basically of two types, running shoes (in general torsionally stiff) and spikes (torsionally flexible). The possibly varying effect of these shoes on the shoe/foot motion in running is not known. The purpose of this investigation was therefore to show whether the pronation angle and the torsion angle differ when running barefoot, with spikes, and with running shoes (forefoot touchdown, N = 9 left and right). A film analysis provided the angular movements of the lower leg, rearfoot, and forefoot as well as pronation and torsion in the frontal plane. The results show that at touchdown the torsional movements with both shoe types are quite different from those of running barefoot. With shoes, the torsion angle is reduced back to zero--with running shoes more than with spikes--and the pronation angle is increased beyond the barefoot values (P less than 0.01). In order to reduce the risk of injury, both shoe types should be improved--the running shoes with respect to torsion and the spikes with respect to pronation.     

Kinematic and kinetic parameters associated with running in different shoes.

The characteristics of the midsole were examined in four pairs of running shoes by a materials test. The variables of interest were the peak acceleration, time to peak acceleration and the kinetic energy absorbed. Ten subjects then ran at a recreational jogging pace (3.5 ms-1) barefoot and in the shoes. An accelerometer secured to the lower tibia was used to measure the peak acceleration and time to peak acceleration associated with footstrike. Subjects were also videoed and a kinematic analysis was undertaken at the knee and ankle joints. The results from the materials test showed that the shoes differed in their midsole characteristics, however, no significant differences (P > 0.05) were observed in the peak acceleration and time to peak acceleration during running in shoes. These variables were significantly greater in the barefoot running condition (P < 0.05), as compared with running in shoes. Small and subtle kinematic differences were observed between the barefoot and shoe conditions. It appears that the differences observed between the shoes in the materials test were not sufficient to elicit the kinematic changes observed between the barefoot and shoe conditions. It is suggested that runners operate within a 'kinetic bandwidth' when responding to impact stresses.     

Rectal temperature after marathon running.

Rectal temperature was measured in 62 male runners who competed in the 1983 Dundee marathon race: all measurements were made immediately after the race. Competitors' times were noted at 5, 10, 15 and 20 miles (8.0, 16.1, 24.1, 32.2 km) and at the finish (26.2 miles, 42.2 km). Mean finishing time of the group was 3 hr 33 min +/- 48 min (mean +/- S.D.; range = 2 hr 17 min-5 hr 11 min). Mean running speed of the group decreased progressively as the distance covered increased. Mean post-race rectal temperature was 38.7 +/- 0.9 degrees C (range 35.6-40.3 degrees C). The post-race temperature was correlated (p less than 0.01) with the time taken to cover the last 6.2 miles (10 km) of the race, but not with the overall finishing time (p greater than 0.05). Only the fastest runners were able to maintain an approximately constant pace throughout the race, whereas the slower runners slowed down progressively. The runners with the highest post-race temperature, although not necessarily the fastest runners, also tended to maintain a steady pace throughout. The runners with the lowest post-race temperature slowed down markedly only over the last 6.2 mile section of the race. The results clearly indicate that runners forced by fatigue or injury to slow down in the latter stages of races held at low ambient temperatures may already be hypothermic or at serious risk of hypothermia.     

The influence of lateral heel flare of running shoes on pronation and impact forces

The purpose of this investigation was to study the influence of the flare at the lateral side of the heel of running shoes on: initial and total pronation; impact forces in heel-toe running; and to explain the results with a mechanical model. The experimental part of the study was performed by using 14 male runners. Their running movement (4 m/s) was quantified by using a force platform and high-speed film (100 frames X s-1). Three shoes were used, identical except in their lateral heel flare, one shoe with a conventional flare of 16 degrees, a second shoe with no flare, and a third shoe with a rounded heel (negative flare). The experimental results indicate that (for the used set of shoes); increasing heel flare increases the amount of initial pronation; changes in heel flare do not affect the magnitude of the total pronation; and changes in heel flare do not alter the magnitude of the impact force peaks. Since shoes with rounded lateral heels do reduce initial pronation, it is speculated that this construction could be used to prevent anterior medial compartment syndrome at the tibia of runners. It was concluded that more research is needed to specify whether the reported result is representative for various shoe types or is shoe specific.     

The effect of different running shoes on treadmill running mechanics and muscle activity assessed using statistical parametric mapping (SPM)

BackgroundDifferences in joint mechanics between running shoes are commonly assessed using discrete parameters, yet statistically significant differences in these parameters between shoes are often scarce with small effect sizes. Statistical parametric mapping (SPM) has been suggested as suitable method for analyzing one-dimensional data such as kinematic, kinetic or muscle intensity time series.Research questionThe purpose of this study was to determine differences in treadmill running mechanics between novel running shoes using SPM.MethodsJoint kinematics, muscle activity and ground reaction force were assessed in 19 rearfoot runners in their own shoes and in two test shoes during treadmill running (test shoe 1: 13 distinct rubber elements in the outer sole, springboard within EVA midsole with posterior elements shifted anteriorly by approximately 1.5 cm; test shoe 2: 17 distinct EVA elements with conventional heel geometry). Joint kinematics were measured using an inertial sensor system, and ground reaction force was measured using an instrumented treadmill.ResultsSPM analysis with repeated measures ANOVA revealed significant reductions in the ankle angle and in tibialis anterior, peroneus longus, vastus medialis and lateralis muscle activity during weight acceptance and in peroneus longus muscle activity during early and late swing and in semitendinosus muscle activity during late swing for the test shoes. Significant differences in muscle activity were observed in the interval of the main activity of the respective muscle. SPM on individual data revealed statistically significant and relevant within-subject differences between conditions in kinematic, muscle activity and ground reaction force patterns.SignificanceInertial sensor systems and SPM may provide an efficient way of detecting changes in joint mechanics between running shoes within runners. Detecting within-subject differences in running mechanics between conditions not only requires statistical criteria but also criteria on the relevance of the magnitude of differences.     

Individual effects of stride length and frequency on shock attenuation during running

Shock attenuation during running is the process of absorbing impact energy due to the foot-ground collision, reducing shock wave amplitude between the foot and head. Shock attenuation is affected by changes in stride length and stride frequency, but it is not clear whether either parameter individually affects shock attenuation. PURPOSE: To identify the independent affects of stride length (SL) and stride frequency (SF) on shock attenuation. METHODS: Subjects ( N = 10) completed three experiments consisting of SL and SF manipulations relative to preferred stride length (PSL) and frequency (PSF). During experiment 1, stride length was manipulated (+15% PSL, PSL, -15% PSL) while stride frequency was always set to PSF. During experiment 2, stride frequency was manipulated (+15% PSF, PSF, -15% PSF) while stride length was always set to PSL. During experiment 3, stride length and stride frequency were manipulated concurrently (+10% PSL/-10% PSF, PSL/PSF, and -10% PSL/+10% PSF). Running velocity was always the product of stride length and stride frequency. Transfer functions were calculated using tibial and forehead surface mounted accelerometer data to represent shock attenuation. RESULTS: Shock attenuation changed only when stride length changed ( P < 0.05). Specifically, shock attenuation increased as stride length increased. CONCLUSION: It was concluded that changes in stride length not stride frequency affected shock attenuation.     

Energy cost of riding bicycles with shock absorption systems on a flat surface.

Bike shock absorption systems reduce the energy variation induced by terrain irregularities, leading to a greater comfort. However, they may also induce an increase in energy expenditure for the rider. More specifically, cross-country racers claim that rear shock absorption systems generate significant energy loss. The energy losses caused by such systems may be divided in terrain-induced or rider-induced. This study aims at evaluating the rider-induced energy loss of modern suspended bicycles riding on a flat surface. Twelve experienced competitive racers underwent three multistage gradational tests (50 to 250 W) on a cross-country bicycle mounted on an electromagnetically braked cycle ergometer. Three different tests were performed on a fully suspended bike, front suspended and non-suspended bicycle, respectively. The suspension mode has no significant effect on VO2. The relative difference of VO2 between the front-suspended or full-suspended bike and the rigid bike reaches a non significant maximum of only 3%. The claims of many competitors who still prefer front shock absorption systems could be related to a possible significant energy loss that could be present at powers superior to 250 W or when they stand on the pedals. It could also be generated by terrain-induced energy loss.     

Effect of intravenous fluid administration on recovery after running a marathon.

After the Rotterdam Marathon on 21 April 1991 (ambient temperature 5.8 degrees C, relative humidity 74%, wind velocity 5 m s-1) data from 66 athletes were analysed for information concerning total recovery and recovery from pain, stiffness, loss of appetite, sleep disturbance and fatigue. The pulse rate, body weight and temperature were measured. The athletes were divided at random into two groups. Thirty-four athletes received an intravenous infusion of 2.5 l of a 2.5% glucose/0.45% NaCl solution. Thirty-two athletes received a placebo infusion of 100 ml 0.9% NaCl. Recovery took 9.2 days in the placebo group and 10.2 days in the infusion group. All athletes had pain and/or stiffness after the marathon. The immediate replacement of 2.5 l of fluid had no significant influence on the rate of total recovery, the number of days with pain or stiffness, the appetite, sleep or fatigue. On the first day after the marathon the pulse rate was increased. The rectal temperature was not affected. The athletes were also divided into fast and slow runners without regard to fluid replacement. Fast runners (those running the race in less than 2 h 55 min) needed more time to recover than slower runners and pain and/or stiffness lasted longer in the fast group. Athletes who equalled or improved their best previous results also needed more time to recover than athletes who did not, although there were no significant differences in pain and stiffness. Athletes did not benefit from immediate fluid replacement after running the 1991 Rotterdam Marathon.     

Effect of hot environmental conditions on physical activity patterns and temperature response of football players

Heat stress may contribute to decreased match performance when football is played in extreme heat. This study evaluated activity patterns and thermal responses of players during soccer matches played in different environmental conditions. Non-acclimatized soccer players (n=11, 20±2 years) played two matches in conditions of moderate heat (MH) and high heat (HH) index. Core temperature (T(c) ) and physical performance were measured using a telemetric sensor and a global positioning system, respectively. The average ambient temperature and relative humidity were MH 34±1 °C and 38±2%; HH 36±0 °C and 61±1%. Peak T(c) in the MH match was 39.1±0.4 °C and in the HH match it was 39.6±0.3 °C. The total distance covered in the first and second halves was 4386±367 and 4227±292 m for the MH match and 4301±487 and 3761±358 m for the HH match. Players covered more distance (P<0.001) in the first half of the HH match than in the second half. In football matches played at high environmental temperature and humidity, the physical performance of the players may decrease due to high thermal stress.