Publications

OBJECTIVE: To evaluate the muscle activation patterns at varying levels of weight-bearing forces during assisted walking with an axillary crutch and a recently designed device that allows weight transfer through the pelvic girdle (ED Walker). DESIGN: Descriptive, repeated measures. SETTING: University-based research laboratory. PARTICIPANTS: Twelve healthy volunteers (age, 39.6+/-13.6 y). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Electromyographic activity was recorded from the anterior tibialis, soleus, biceps femoris, and vastus lateralis muscles on a test leg during assisted axillary crutch and ED Walker ambulation. Force platform readings measured weight-bearing load (non, light, heavy). These values were normalized to normal walking gait. RESULTS: In the vastus lateralis and soleus muscles, both devices allowed for approximately 50% and 65% reductions in electromyographic activity during the non-weight-bearing condition. During crutch ambulation, electromyographic activity of the soleus was significantly reduced compared with that required for normal walking at all levels of weight-bearing load. In the vastus lateralis for the weight-bearing conditions, the ED Walker required significantly higher electromyographic activity than crutch ambulation (light: 105.0%+/-12.3% vs 72.7%+/-10.1%; heavy: 144.8%+/-23.5% vs 100.0%+/-13.5%). Both devices required similar peak vertical ground reaction forces during the heavy weight-bearing conditions (crutch: 75%+/-1.6%; ED Walker: 73%+/-1.8%), whereas axillary crutch gait produced less force than the ED Walker in the light condition (32%+/-2.0% vs 48%+/-1.6%). CONCLUSIONS: During walking with assistive devices, muscle activation patterns varied with weight-bearing load. The leg extensor muscles appeared to incur a greater reduction in muscle activity when compared with their flexor counterparts. Additionally, the ED Walker and axillary crutch differed with respect to their muscle activity levels and weight-bearing characteristics. Clinically, knowledge of these muscle activity and force characteristics may aid in the decision-making process of prescribing a device type and timeline to follow in restoring weight-bearing loads.

The purposes of this study were 1) to evaluate gender differences in back extensor endurance capacity during isometric and isotonic muscular contractions, 2) to determine the relation between absolute load and endurance time, and 3) to compare men [n = 10, age 22.4 +/- 0.69 (SE) yr] and women (n = 10, age 21.7 +/- 1.07 yr) in terms of neuromuscular activation patterns and median frequency (MF) shifts in the electromyogram (EMG) power spectrum of the lumbar and hip extensor muscles during fatiguing submaximal isometric trunk extension exercise. Subjects performed isotonic and isometric trunk extension exercise to muscular failure at 50% of maximum voluntary contraction force. Women exhibited a longer endurance time than men during the isometric task (146.0 +/- 10.9 vs. 105.4 +/- 7.9 s), but there was no difference in endurance performance during the isotonic exercise (24.3 +/- 3.4 vs. 24.0 +/- 2.8 repetitions). Absolute load was significantly related to isometric endurance time in the pooled sample (R(2) = 0.34) but not when men and women were analyzed separately (R(2) = 0.05 and 0.04, respectively). EMG data showed no differences in neuromuscular activation patterns; however, gender differences in MF shifts were observed. Women demonstrated a similar fatigability in the biceps femoris and lumbar extensors, whereas in men, the fatigability was more pronounced in the lumbar musculature than in the biceps femoris. Additionally, the MF of the lumbar extensors demonstrated a greater association with endurance time in men than in women (R(2) = 0.45 vs. 0.19). These findings suggest that gender differences in muscle fatigue are influenced by muscle contraction type and frequency shifts in the EMG signal but not by alterations in the synergistic activation patterns.

STUDY DESIGN: This was a descriptive study involving 20 healthy individuals. OBJECTIVES: To evaluate the neuromuscular activation patterns of the lumbar paraspinal and hip extensor muscles during isotonic trunk extension exercise. SUMMARY OF BACKGROUND DATA: Few studies have evaluated the effect of muscle fatigue on the lumbar musculature during isotonic exercise. METHODS: Electromyographic activity was recorded continuously from the lumbar paraspinal, gluteus maximus, and biceps femoris muscles during isotonic trunk extension exercise performed to muscular failure. Root mean squared electromyography was determined over the concentric portion of each repetition, and polynomial regression analysis was used to describe the association between fatigue and the recruitment patterns. RESULTS: The lumbar paraspinals demonstrated an increase in the electromyogram signal up to 57.9% of maximal fatigue, at which point decrements in electromyography were observed (lumbar [quadratic curve] R2 = 0.0807, SEE = 0.228; beta2 = -8.245(-5)) (P 0.000). Associated with fatigue, the gluteus maximus demonstrated an increase in electromyography, with an exponential breakpoint occurring at 35.9% of maximal fatigue (gluteus maximus [quadratic curve]: R2 = 0.5059, SEE = 0.865; beta2 = 0.00017) (P = 0.014). The biceps femoris demonstrated a linear increase in electromyography with fatigue (R2 = 0.4667, SEE = 0.284; beta2 = 0.0091) (P 0.000). To further investigate the derecruitment of the lumbar extensors associated with fatigue, study participants were analyzed individually with regression analyses. Results revealed that the majority of study participants (68.5%) demonstrated a significant decrease (quadratic bend) in lumbar electromyography, with decrements in muscle activity beginning at 53% of maximum. CONCLUSION: During fatiguing trunk extension exercise, an increase in the lumbar paraspinal electromyogram signal occurs up to approximately 55% of maximum fatigue, at which point a decrease in electromyography is observed. Associated with this derecruitment is a concomitant increase in hip extensor muscle activity, suggesting that as the lumbar musculature becomes fatigued, these muscles allow for continuation of the exercise.

OBJECTIVE: To evaluate the effects of exercise intensity and multiple sets on muscle activation patterns during trunk extension exercise. DESIGN: Descriptive, repeated measures. SETTING: University-based musculoskeletal research laboratory. PARTICIPANTS: Twenty volunteers recruited from a university setting. INTERVENTION: Not applicable. MAIN OUTCOME MEASURES: Electromyographic activity was recorded from the L3-4 paraspinal region, gluteus maximus, and biceps femoris muscles during multiple sets of trunk extension exercise at intensities representing 40%, 50%, and 70% of peak isometric force. RESULTS: As exercise intensity increased, the electromyographic activity of the gluteus maximus increased to a greater extent than the activity of the paraspinal region. At the 50% intensity level, biceps femoris electromyographic activity was significantly greater than the paraspinal region electromyographic activity, whereas at the 70% intensity no differences were found between muscles. During multiple sets of exercise at the same intensity a muscle by set interaction was observed. This interaction revealed that with respect to other muscle groups, the electromyographic activity of the gluteus maximus increased between sets 1 and 2, whereas electromyographic decrements occurred in the paraspinal region. During exercise at the 40% intensity level, biceps femoris electromyographic activity increased to a greater extent between sets 1 and 2 when compared with the paraspinal region. CONCLUSION: Exercise intensity and multiple sets result in alterations in muscle recruitment patterns of the lumbar and hip extensor muscles. These findings raise questions as to the efficacy of added loading and multiple sets during trunk extension exercise.