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Nicholas D. Parr, Chris J. Hass and Mark D. Tillman

Cellular phone texting has become increasingly popular, raising the risk of distraction-related injuries. The purpose of this study was to compare alterations in gait parameters during normal gait as opposed to walking while texting. Thirty able-bodied young adults (age = 20 ± 2 y, height = 171 ± 40 cm, mass = 61.7 ± 11.2 kg) who reported texting on a regular basis were tested using an 11-camera optical motion capture system as they walked across an 8 m, obstacle-free floor. A reduction in velocity (P < .05) was seen along with additional significant changes in spatial and temporal parameters. Specifically, step width and double stance time increased, while toe clearance, step length, and cadence decreased. Although many of the changes in spatial and temporal parameters generally accompany slowed gait, the complex distraction task used here may have amplified these potentially deleterious effects. The combination of the slower gait velocity and decrease in attention to the surrounding environment suggests that an individual who is texting while walking could be at a greater risk of injury. Tripping injuries while texting could be more likely due to the decreased toe clearance. In addition, increased step width may increase the likelihood of stepping on an unstable surface or colliding with obstacles in close proximity.

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Dana M. Otzel, Chris J. Hass, Erik A. Wikstrom, Mark D. Bishop, Paul A. Borsa and Mark D. Tillman

Context: Following a lateral ankle sprain, ∼40% of individuals develop chronic ankle instability (CAI), characterized by recurrent injury and sensations of giving way. Deafferentation due to mechanoreceptor damage postinjury is suggested to contribute to arthrogenic muscle inhibition (AMI). Whole-body vibration (WBV) has the potential to address the neurophysiologic deficits accompanied by CAI and, therefore, possibly prevent reinjury. Objective: To determine if an acute bout of WBV can improve AMI and proprioception in individuals with CAI. Design and Participants: The authors examined if an acute bout of WBV can improve AMI and proprioception in individuals with CAI with a repeated-measures design. A total of 10 young adults with CAI and 10 age-matched healthy controls underwent a control, sham, and WBV condition in randomized order. Setting: Biomechanics laboratory. Intervention: WBV. Main Outcome Measures: Motoneuron pool recruitment was assessed via Hoffmann reflex (H-reflex) in the soleus. Proprioception was evaluated using ankle joint position sense at 15° and 20° of inversion. Both were assessed prior to, immediately following, and 30 minutes after the intervention (pretest, posttest, and 30mPost, respectively). Results: Soleus maximum H-reflex:M-response (H:M) ratios were 25% lower in the CAI group compared with the control group (P = .03). Joint position sense mean constant error did not differ between groups (P = .45). Error at 15° in the CAI (pretest 0.8 [1.6], posttest 2.0 [2.8], 30mPost 2.0 [1.9]) and control group (pretest 0.8 [2.0], posttest 0.6 [2.9], 30mPost 0.5 [2.1]) did not improve post-WBV. Error at 20° did not change post-WBV in the CAI (pretest 1.3 [1.7], posttest 1.0 [2.4], 30mPost 1.5 [2.2]) or control group (pretest −0.3 [3.0], posttest 0.8 [2.1], 30mPost 0.6 [1.8]). Conclusion: AMI is present in the involved limb of individuals with CAI. The acute response following a single bout of WBV did not ameliorate the presence of AMI nor improve proprioception in those with CAI.

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Mark D. Tillman and John W. Chow

Column-editor : Thomas W. Kaminski

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Michael A. Machek, Christine B. Stopka, Mark D. Tillman, Suzanne M. Sneed and Keith E. Naugle


To examine the effects of a resistance-training program on athletes with intellectual disabilities (ID).


2-way (2 × 2), repeated-measures analysis of variance on 2 groups (males and females); 30 Special Olympics (SO) athletes, age 16–22 (16 males, 14 females).

Intervention/Outcome Measures:

Resistance training, twice per week, for 3 months on Med-X weight equipment. Exercises tested: chest press, abdominal crunch, seated row, overhead press, seated dip, lower back extension, and biceps curl. The weight lifted and the number of repetitions performed were used to determine predicted 1-repetition max (1RM).


All participants as a group increased significantly in predicted 1RM for each exercise performed. Males were stronger than females for 5 of the 7 exercises. A significant interaction effect between genders was demonstrated for the seated dip.


Significant strength gains can be accomplished by adolescents with ID via a supervised resistance-training program.

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Jaimie A. Roper, Ryan T. Roemmich, Mark D. Tillman, Matthew J. Terza and Chris J. Hass

Interventions that manipulate gait speed may also affect the control of frontal plane mechanics. Expanding the current knowledge of frontal plane adaptations during split-belt treadmill walking could advance our understanding of the influence of asymmetries in gait speed on frontal plane mechanics and provide insight into the breadth of adaptations required by split-belt walking (SBW). Thirteen young, healthy participants, free from lower extremity injury walked on a split-belt treadmill with belts moving simultaneously at different speeds. We examined frontal plane mechanics of the ankle, knee, and hip joints during SBW, as well as medio-lateral ground reaction forces (ML-GRF). We did not observe alterations in the frontal mechanics produced during early or late adaptation of SBW when compared to conditions where the belts moved together. We did observe that ML-GRF and hip moment impulse of the fast limb increased over time with adaptation to SBW. These results suggest this modality may provide a unique therapy for individuals with gait pathologies, impairments, or compensation(s).

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Mark D. Tillman, Chris J. Hass, John W. Chow and Denis Brunt

During ballistic locomotion and landing activities, the lower extremity joints must function synchronously to dissipate the impact. The coupling of subtalar motion to tibial and knee rotation has been hypothesized to depend on the dynamic requirements of the task. This study was undertaken to look for differences in the coupling of 3-D foot and knee motions during walking, jogging, and landing from a jump. Twenty recreationally active young women with normal foot alignment (as assessed by a licensed physical therapist) were videotaped with high-speed cameras (250 Hz) during walking, jogging, hopping, and jumping trials. Coupling coefficients were compared among the four activities. The ratio of eversion to tibial rotation increased from the locomotion to the landing trials, indicating that with the increased loading demands of the activity, the requirements of foot motion increased. However, this increased motion was not proportionately translated into rotation of the tibia through the subtalar joint. Furthermore, the ratio of knee flexion to knee internal rotation increased significantly from the walking to landing trials. Together these findings suggest that femoral rotation may compensate for the increase in tibial rotation as the force-dissipating demands of the task increase. The relative unbalance among the magnitude of foot, tibial, and knee rotations observed with increasing task demands may have direct implications on clinical treatments aimed at reducing knee motion via controlling motion at the foot during landing tasks.

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Mark D. Tillman, Rachel M. Criss, Denis Brunt and Chris J. Hass

The purposes of this study were to analyze double-limb, dominant-limb, and nondominant-limb landings, each with a two-footed takeoff, in order to detect potential differences in muscle activity and ground reaction forces and to examine the possible influence of leg dominance on these parameters. Each of the three jump landing combinations was analyzed in 11 healthy female volleyball players (age 21 ± 3 yrs; height 171 ± 5 cm, mass 61.6 ± 5.5 kg, max. vertical jump height 28 ± 4 cm). Ground reaction forces under each limb and bilateral muscle activity of the vastus medialis, hamstrings, and lateral gastrocnemius muscles were synchronized and collected at 1,000 Hz. Normalized EMG amplitude and force platform data were averaged over five trials for each participant and analyzed using repeated-measures ANOVA. During the takeoff phase in jumps with one-footed landings, the non-landing limb loaded more than the landing limb (p = 0.003). During the 100 ms prior to initial contact, single-footed landings generated higher EMG values than two-footed landings (p = 0.004). One-footed landings resulted in higher peak vertical loading, lateral loading, and rate of lateral loading than two-footed landings (p < 0.05). Trends were observed indicating that muscle activation during one-footed landings is greater than for two-footed landings (p = 0.053 vs. p = 0.077). The greater forces and rate of loading produced during single-limb landings implies a higher predisposition to injury. It appears that strategic planning and training of jumps in volleyball and other jumping sports is critical.

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Phillip Conatser, Keith E. Naugle, Christine Stopka and Mark D. Tillman

Edited by Shane Caswell

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Chris J. Hass, Elizabeth A. Schick, John W. Chow, Mark D. Tillman, Denis Brunt and James H. Cauraugh

Epidemiological evidence suggests the incidence of injury in female athletes is greater after the onset of puberty and that landing from a jump is a common mechanism of knee injury. This investigation compared lower extremity joint kinematics and joint resultant forces and moments during three types of stride jump (stride jump followed by a static landing; a ballistic vertical jump; and a ballistic lateral jump) between pre- and postpubescent recreational athletes to provide some insight into the increased incidence of injury. Sixteen recreationally active postpubescent women (ages 18–25 years) and 16 recreationally active prepubescent girls (ages 8–11 years) participated in this study. High speed 3D videography and force plate data were used to record each jumper’s performance of the stride jumps, and an inverse dynamic procedure was used to estimate lower extremity joint resultant forces and moments and power. These dependent variables were submitted to a 2 × 3 (Maturation Level × Landing Sequence) MANOVA with repeated measures on the last factor. The findings indicated that postpubescents landed with the knee more extended (4.4°) and had greater extension moments (approximately 30% greater hip and knee extension moments) and powers (40% greater knee power). Further, the post-pubescent athletes had greater knee anterior/posterior forces as well as medio-lateral resultant forces. The differences found between the two groups suggest there may be anatomical and physiological changes with puberty that lead to differences in strength or neuromuscular control which influence the dynamic restraint system in these recreational athletes. A combination of these factors likely plays a role in the increased risk of injury in postpubescent females.