GCD Variables. Steps and Strides. Walking Speed. Cadence. Stride Length

Transcription

1 Variables Steps and Strides Each time a leg goes forward, it makes a step the right leg moves forward to make a right step and then the left leg moved forward for a left step. When a right and left step has occurred, we say the individual has taken a one gait cycle, or stride. The interval that it takes for this to occur is called the stride time. A gait cycle starts with the initial contact (usually a heel contact in normal gait) of one foot and the end of the cycle occurs with the next contact of the same (ipsilateral) foot. In normal walking the steps are symmetrical and toe-off occurs at about 62% of the gait cycle time, dividing the cycle into stance and swing phases. Walking Speed Walking Speed can be calculated from the equation Speed = Distance / Time. A normal adult walking speed is about 1.5 m/s, and considerable disability occurs if it drops below 1 m/s. Cadence The number of steps taken by the subject per minute is called the cadence. There are two steps (left and right) in every stride, and 60 seconds in one minute, we can convert from steps per minute to strides per second by dividing by 120. Stride time is simply 120/Cadence. Natural adult cadence is about 120 steps/minute or one gait cycle per second. Vicon PIG stores cadence in terms of steps/minute while the variables store cadence in terms of strides/second which must be multiplied by 120 to get steps/minute. Stride Length Subject walking speed is the product of cadence and stride length. Cadence is expressed in steps per minute so it must be divided by 120 to yield the equation Speed = (Cadence x Stride Length) / 120. Speed is usually measured by determining the time taken to cover a fixed distance while counting the number of steps taken, thus Stride Length = (120 x Speed) / Cadence.

2 Gait Cycle Variables File Cadence Cadence stride/sec 1 Walking rate. The units are strides per second so that cadence in steps per minute can always be calculated (Cadence*120) even from unilateral trials. Note that Left and Right Cadences may differ. Stride Time StrideTime sec/stride 1 This is the inverse of Cadence and is also known as per Gait Cycle Time. It is used to normalize many other events and timings to percentage of Gait Cycle. Opposite Foot Off OppositeFootOff % cycle 1 The instant of opposite foot off. Opposite Foot Contact OppositeFootContact % cycle 1 The instant of opposite foot contact. In perfectly symmetrical gait, this would be 50% - however gait is not always symmetrical. Step Time StePTime % cycle 1 The time from the instant of opposite foot contact to the end of the gait cycle. Single Support SingleSupport % cycle 1 The time spent on one foot only; equivalent to opposite Swing Phase. Double Support DoubleSupport % cycle 1 The total time spent on both feet. There are two periods of double support, at the start and end of the Stance Phase. Foot Off FootOff % cycle 1 The instant of foot off, also known as Toe Off. Stride Length StrideLength m 1 The distance moved in direction of walking by the forefoot marker from start to end of the Gait Cycle. Step Length StePLength m 1 The distance in the direction of walking between opposite forefoot marker at opposite foot contact and forefoot marker at foot contact. Note that the value of this variable depends upon a symmetrical placement of forefoot markers. Walking Speed Speed m/sec 1 The average speed over the analyzed Gait Cycle. Vicon Plug-in-Gait generates these variables and stores them in the C3D file ANALYSIS group. The values stored in the C3D file are calculated based on the first full gait cycle available in the trial.

3 Model Parameter Variables File BodyMass Kg 1 Subject weight Height mm 1 Subject height LLegLength mm 1 Left Leg length RLegLength mm 1 Right Leg length LKneeWidth mm 1 Left Knee width RKneeWidth mm 1 Right Knee width LAnkleWidth mm 1 Left Ankle width RAnkleWidth mm 1 Right Ankle width InterAsisDistance mm 1 The distance between the two ASIS markers LAsisTrocanterDistance mm 1 Left ASIS marker to Left Trochanter marker distance note the odd spelling in the MP file variable. RAsisTrocanterDistance mm 1 Right ASIS marker to Right Trochanter marker distance note the odd spelling in the MP file variable. LTibialTorsion degrees 1 Left Tibial Torsion RTibialTorsion degrees 1 Right Tibial Torsion LThighRotation degrees 1 Left Thigh rotation RThighRotation degrees 1 Right Thigh rotation LShankRotation degrees 1 Left Shank rotation RShankRotation degrees 1 Right Shank rotation LStaticPlantFlex degrees 1 Left Static Planter Flexion RStaticPlantFlex degrees 1 Right Planter Flexion LStaticRotOff degrees 1 Left static foot rotation offset RStaticRotOff degrees 1 Right static foot rotation offset

4 Vicon Plug-in-Gait Variables File PelvisAngles-X PelvicTilt degrees 51 Anterior tilting of the pelvis about a lateral horizontal axis. PelvisAngles-Y PelvicObliquity degrees 51 Rotation of the pelvis about an anterior horizontal axis. PelvisAngles-Z PelvicRotation degrees 51 Rotation of the pelvis about a vertical axis. HipAngles-X HipFlexExt degrees 51 Flexion of the hip. HipAngles-Y HipAbAdduct degrees 51 Abduction of the hip. HipAngles-Z HipRotation degrees 51 External rotation of the hip. KneeAngles-X KneeFlexExt degrees 51 Flexion of the knee. KneeAngles-Y KneeValgVar degrees 51 Abduction of the knee. KneeAngles-Z KneeRotation degrees 51 Rotation of the knee. AnkleAngles-X DorsiPlanFlex degrees 51 Dorsiflexion of the ankle. FootBasedDorsiPlanFlex degrees 51 Measured about an axis normal to the plane defined by [knee joint][ankle joint]["corrected toe marker"] where the he "corrected toe marker" is the position of the toe marker as corrected by processing of a VCM static trial. In other words, this angle approximates the reverse the Grood and Suntay convention at the ankle joint - since it is calculated without reference to the ankle joint flexion axis, the Tibial Torsion measurement has no effect. AnkleAngles-Z FootRotation degrees 51 External rotation of the ankle. ShankBasedFootRotation degrees 51 Measured about the [ankle joint][knee joint] axis and is the angle between the anterior shank axis and the projection of the [ankle joint]["corrected toe marker"*] vector into the transverse plane of the shank where the "corrected toe marker" is the position of the toe marker as corrected by processing of a VCM static trial. This angle approximates the reverse the Grood and Suntay convention at the ankle joint and as it is calculated without reference to the ankle joint flexion axis, the Tibial Torsion measurement has no effect. FootProgressionAngles-Z FootProgression degrees 51 Rotation of the foot about a vertical axis. HipMoment-X HipFlexExtMoment Nm/kg 51 Flexion component of resultant intersegmental moment, HipMoment-Y HipAbAdductMoment Nm/kg 51 Abduction component of resultant intersegmental moment, HipMoment-Z HipRotationMoment Nm/kg 51 Rotation component of resultant intersegmental moment, KneeMoment-X KeeFlexExtMoment Nm/kg 51 Flexion component of resultant intersegmental moment, KneeMoment-Y KneeValgVarMoment Nm/kg 51 Abduction component of resultant intersegmental moment, KneeMoment-Z KneeRotationMoment Nm/kg 51 Rotation component of resultant intersegmental moment, AnkleMoment-X DorsiPlanFlexMoment Nm/kg 51 Flexion component of resultant intersegmental moment, AnkleMoment-Y FootAbAdductMoment Nm/kg 51 Abduction component of resultant intersegmental moment,

5 File AnkleMoment-Z FootRotationMoment Nm/kg 51 Rotation component of resultant intersegmental moment, HipPower-Z HipPower watts/kg 51 Total power generated due to hip joint movement. HipFlexExtPower watts/kg 51 Flexion component of total power generated due to hip joint HipAbAdductPower watts/kg 51 Abduction component of total power generated due to hip joint movement (not calculated by PIG) HipRotationPower watts/kg 51 Rotation component of total power generated due to hip joint KneePower-Z KneePower watts/kg 51 Total power generated due to knee joint movement. KneeFlexExtPower watts/kg 51 Flexion component of total power generated due to knee joint KneeValgVarPower watts/kg 51 Abduction component of total power generated due to knee joint movement (not calculated by PIG) KneeRotationPower watts/kg 51 Rotation component of total power generated due to knee AnklePower-Z AnklePower watts/kg 51 Total power generated due to ankle joint movement. GroundReactionForce-X GroundReactionForce-Y GroundReactionForce-Z GroundReactionMoment-X GroundReactionMoment-Y GroundReactionMoment-Z HipForce-X HipForce-Y HipForce-Z KneeForce-X KneeForce-Y KneeForce-Z AnkleForce-X AnkleForce-Y AnkleForce-Z DorsiPlanFlexPower watts/kg 51 Dorsiflexion component of total power generated due to ankle AnkleAbAdductPower watts/kg 51 Abduction component of total power generated due to ankle AnkleRotationPower watts/kg 51 Rotation component of total power generated due to ankle The Ground Reaction Forces, Moments and Joint Forces calculated by Plug-in-Gait are normalized by the MP file variable Bodymass which is entered in kilograms by the user when Plug-in-Gait is run. The Plug-in-Gait function does not appear to perform any sanity checks for this value so that the values of these variables are entirely dependent on the user entering the correct value for BodyMass. ReportGenerator allows this normalization to be removed for compatibility with files produced by VCM.