Access Type

Open Access Dissertation

Date of Award

January 2018

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Exercise and Sport Science

First Advisor

Qin Lai

Abstract

Pilot Part 1: The purpose was to investigate the effect of a perceived exertion based cadence on lower extremity muscle activation, as measured by surface electromyography (EMG) on a recumbent cross trainer. The purpose of this investigation was to study the EMG activity of 12 lower extremity muscles during five different stepping protocols; perceived exertion based self-selected (SS) cadence with level 1 resistance (SSL1), SS cadence with level 8 resistance (SSL8), +20% SS cadence (SS+20), -20% SS cadence (SS-20), and at a set 80 steps per minute at resistance level 1 (80L1). In order to determine SS cadence each participant performed 10 minutes (min) pretest of stepping with a rate of perceived exertion of 12 to16. Participants then performed all five protocols in randomized order with 5 mins of rest between each protocol. Both mean (mEMG) and peak (pEMG) normalized amplitudes were recorded from the rectus femoris (RF), vastus medialis oblique (VMO), semitendinosus (ST), tibialis anterior (TA), medial gastrocnemius (MG) and soleus (SOL) bilaterally. Healthy participant’s (n = 22, aged 23.52 ± 4.23 years) SS cadence was 123.86±18.12 steps/min. SSL8 and SS+20 produced the highest mEMG and pEMG in all muscle groups (p<.05). Generally, SSL1, SS-20 and 80L1 did not differentially activate muscles based on mEMG and pEMG. The present findings indicated that increased resistance (SSL8) and increased step cadence (SS+20) resulted in the greatest activation of lower extremity muscles during recumbent stepping.

Pilot Part 2: Muscle recruitment becomes more efficient as a result of task-specific training. Although the muscle activity of recumbent stepping has been studied previously, it remains unclear if an individual alters recruitment as they acclimate to the stepping motion. The purpose of this study was to measure the change in EMG activity between minute (min) 2 and min 4 of a 5 min stepping bout. EMG was measured bilaterally at 6 separate lower extremity muscles during five different stepping protocols (self-selected level 1 [SSL1], self-selected level 8 [SSL8], +20% self-selected [SS+20], -20% self-selected [SS-20], and 80 steps per min resistance level 1 [80SL1]). 22 healthy male and female adults (aged = 23.52 ± 4.23 years) signed an informed consent prior to the study. Self-selected cadence was established during 10 mins of stepping with a RPE between 12 and 16. Participants then performed all 5-min protocols in randomized order with 5 min of rest between each. Due to parametric violations, mean EMG (mEMG) and peak EMG (pEMG) were analyzed with non-parametric tests. A 1 x 4 Friedman test was conducted to determine statistical significant difference in mEMG and pEMG between min 2 and min 4 of stepping in each muscle. Following a statistically significant Friedman test (p<.05), a post hoc Wilcoxon Signed Rank test (WSRT) was conducted. Participants' self-selected cadence was 126.80 ± 17.87 steps/min. WSRT showed a significant reduction in mEMG activation at min 4 in 5 muscles (rectus femoris [RF], vastus medialis oblique [VMO], semitendinosus [ST], tibialis anterior [TA]) at 80SL1, VMO at SS+20% and RF and VMO at SS-20, (p<.01). WSRT showed a significant reduction in pEMG activation of VMO at min 4 in all protocols, but higher pEMG at min 4 in ST in SSL1 and SSL8, soleus in SSL1 and TA in SS+20. Results indicate a higher level of learning, as measured by the reduction of mEMG during min 4 at protocols below the subject’s self-selected pace. At a significantly lower cadence, it is presumed that a new motor pattern was acquired to adapt to the stepping demands.

NuStep Cross Trainer vs. Treadmill: The NuStep Recumbent Cross Trainer relies on similar neural networks as gait. Therefore, neurologically impaired individuals may improve walking ability after exercise on the NuStep. The purpose of this investigation was to measure the effect of two exercise mode (NuStep Recumbent Cross Trainer vs. Treadmill) on intra-exercise muscle activity (as measured by mean electromyography) and post exercise spatial and temporal gait parameters during a 3 x 10m hallway walk. 34 participants were divided into two groups; chronic stroke (10 ± 5 years post cerebral vascular accident) and an age and sex matched control. In order to determine SS cadence each participant performed 10 minutes (min) pretest of stepping with a rate of perceived exertion (RPE) of 12 to16. Participants then performed two 5 minute exercise bouts on each mode. Mean electromyography (mEMG) values were normalized to maximum voluntary contraction and were recorded from the rectus femoris (RF), vastus medialis oblique (VMO), semitendinosus (ST), tibialis anterior (TA), medial gastrocnemius (MG) and soleus (SOL) bilaterally. Stroke (n = 15) and healthy (n = 19) did not differ in age (Mdn: 66 vs. 57, respectively) or BMI (Stroke: M = 27.02, SD = 4.57 vs. Healthy: M = 26.46, SD = 4.63), p<.05. Healthy participants were stronger at all joints, p<.025. Goniometer data was measured at the hip, knee and ankle. Range of motion change (∆ROM) was calculated (maximum-minimum degree; ∆ROM). There was no statistical differences between the TM and NS in ∆ROM. The TM elicited a higher mEMG on a majority of the observed muscles. The NuStep Cross Trainer immediately improved gait parameters (i.e. decreased stance % and increased swing %) on the non-affected leg following a 5-minute stepping protocol.

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