Methods

Data from one male subject (age: 33 years; mass: 80 kg; height: 1.8 m), experienced in deep water running (DWR) and treadmill running (TMR), were analyzed to compare mechanics of DWR and TMR. Anatomical landmarks (base of rib cage, greater trochanter, knee joint approximation, lateral malleolus, heel and fifth metatarsal) were used to calculate hip, knee and ankle angles. Electromyography

The subject was instrumented with an electromyography (EMG) transmitting unit (Coulbourn Instruments, Leigh Valley, PA) using surface EMG leads to measure the muscle activity of the rectus femoris and biceps femoris. The leads were waterproofed by using an adhesive (Smith & Nephew United, Inc., FL) and placing plastic wrap over the area. Additionally, a hard shell was fixed over the area to prevent water pressure from affecting the EMG signal, recorded at 500 Hz. The leads were placed approximately 1.5 cm apart from each other.

 
(Is this a cadaver leg?) Video

A right side sagittal plane video record (30 Hz) was obtained during both modes of exercise. During DWR, an underwater window was used to view the activity. The camera was placed close to the window, with the lens parallel to the window plane. The field of view was such that the subject's waist was approximately in direct line with the lens of the camera. The camera to subject distance was approximately 15 meters. This set up has been determined to minimize perspective error during underwater video analysis (Griffin, 1993).

Testing Protocol

Testing required completion of 3 levels of intensity of exercise during DWR and TMR. During DWR, two styles were tested, "cross-country" (C1) and "high-knee" (C2), with C1 preceding C2. The cross-country style is an action that is qualitatively similar to TMR. The action requires the subject to, in effect, over stride. The high-knee style of DWR is similar to marching in place, with the legs going through a piston like action.

The levels of intensity of exercise were based on Borg's 6-20 point Rating of Perceived Exertion (RPE) scale (Borg, 1982). An RPE rating of 11 was used for the first level, 13 and 15 ratings for the second and third levels, respectively. After gradually increasing the level of intensity to reach the particular RPE, the subject exercised for approximately 30 to 60 seconds while EMG and heart rate (HR) data were collected. Additionally, EMG data were collected prior to each exercise level with the subject in a relaxed state. The multiple resting measurements were used to establish an EMG baseline for each muscle group.

The levels of intensity during TMR were based on the HR recorded during DWR. Because the HR was similar during 3 of the 6 levels of exercise during DWR, the subject completed only 3 levels of intensity during TMR. Intensity of exercise was gradually increased until the predetermined HR was attained by increasing treadmill speed 0.023 m/s every 30 s with a starting speed of 2.35 m/s. After completion of the 3 levels of exercise, it was determined that water had leaked into the lead seal and corrupted the EMG signal. Therefore, the leads were removed, dried off and cleaned. After the muscle site had been dried off, the leads were repositioned and 3 levels of exercise were repeated, once again matching DWR HR. The video analysis was completed using the first data set.

Analysis

Kinematic

Three consecutive right side strides from each level of exercise were digitized using Aerial Performance Analysis System, Inc. (APAS) software package. Markers were smoothed using a digital filter with the cutoff frequency ranging from 4-10 Hz, as determined from a spectral analysis and examining the 1st, 2nd, and 3rd time derivatives. Data were interpolated to 100% and ensemble data sets were generated using laboratory software.

In order to compare the changes in angle during running, a stride was defined as the time between two consecutive right heel contacts. Two phases were defined within a stride: support and swing. During TMR, support was defined as the time between the discrete events of heel contact and toe off. The swing phase was considered the time between toe off and the next heel contact. Unlike TMR, there was no ground contact during DWR. Therefore, "stance" was defined as the time between the discrete event of when the foot transitioned from a forward to backward action (i.e. heel contact) and the time when the foot transitioned from a backward to forward action (i.e. toe off). This phase is analogous to a "propulsive" phase.

During DWR C2, it was difficult to identify a discrete event analogous to heel contact and toe off due to the "piston" like action of the legs. This action is qualitatively different than the action during TMR. Nevertheless, consistent with the analogy of support and propulsive phases in the previous example, support was defined as the time between maximum hip flexion and maximum hip extension.

Electromyography

The EMG data were processed by creating a linear envelope of the full-wave rectified signal. Due to leakage of the seal, EMG data were corrupted for trials 2 and 3 during DWR C2 and TMR. The TMR trials were repeated after EMG leads were dried off and replaced.

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