In this study, lower extremity kinematics and electromyography (EMG) from eight muscles were examined in high speed treadmill running in both incline and level conditions. Electromyography has been useful in comparing muscular activity among different movements. The electromyography patterns of lower extremity muscles have been well documented for treadmill running both on the level and at moderate grades. Recent sprint training regimens have included high speed treadmill running at grades of over 30%. A main goal of these training protocols is to develop muscular power during both stance and recovery phases of the sprinting cycle. The purpose of this study was to compare the joint kinematics and muscle activity of the lower extremity during high speed incline treadmill running at 4.5 m/s and 30% grade with level running at either the same speed or the same stride frequency.
Twelve healthy college-aged males (mass 68 ± 5 kg, height 1.76 ± 0.04 m) skilled in both level and incline treadmill running ran in three randomly ordered conditions: 4.5 m/s and 30% incline (INC); level running at the same stride frequency as the incline (LSF); and level running at the same speed as the incline (LSS).
Five trials of electromyography data from tibialis anterior (TA), medial gastrocnemius (GA), soleus (SOL), rectus femoris (RF), vastus lateralis (VL), medial hamstrings (MH), biceps femoris (BF), and gluteus maximus (GM) were collected for each condition using pre-amplified Ag/AgCl surface electrodes. The signals were amplified and sampled at 1000 Hz (12-bit A/D). Sagittal plane motion of the right lower extremity was recorded with 200 Hz video; a footswitch and led system was used to identify stance phase and to synchronize the video and electromyography data.
Using fourth order, dual-pass Butterworth filters, the raw electromyography data were high-pass filtered at 20 Hz to eliminate movement artifact, then full-wave rectified and low-pass filtered at 12 Hz to obtain linear envelopes. Electromyography amplitudes were scaled using standard isometric contractions. Lower extremity joint angle profiles were calculated from the video data. Ensemble curves were calculated for electromyography and angle data for each condition. A repeated measures analysis of variance (ANOVA) was used to detect differences between locomotion conditions for selected measures of the joint angle and electromyography data. The alpha level was set a priori at p < 0.05.
While the general profiles of joint angles were similar in all conditions, all lower extremity joints were significantly more flexed at footstrike in the 4.5 m/s and 30% incline condition (p < 0.001). Further, hip and knee extension ranges of motion (ROM) were significantly larger in the 4.5 m/s and 30% incline condition in late stance (p < 0.01). For the stance phase, the medial gastrocnemius, soleus, rectus femoris, vastus lateralis, and gluteus maximus displayed significantly greater electromyography activity during the 4.5 m/s and 30% incline condition (p < 0.001), while the corresponding activities of medial hamstrings and biceps femoris were lower. With the exception of the medial gastrocnemius and tibialis anterior, electromyography patterns during the swing phase were similar for all muscles between 4.5 m/s and 30% incline and level running at the same stride frequency as the incline. In addition, the level running at the same stride frequency as the incline condition elicited significantly greater electromyography activity than level running at the same speed as the incline for all muscles at key points in the gait cycle. The figure shows ensemble linear envelope patterns normalized to %stride. Toeoff is indicated by the vertical lines for each condition.
The electromyography patterns in the level conditions were very similar to those found in previous studies. The most striking difference in the electromyography patterns between the incline and level conditions was the increase in stance phase activity of the mono-articular muscles soleus, vastus lateralis, and gluteus maximus and the bi-articular medial gastrocnemius and rectus femoris. Recent studies have suggested that mono-articular muscles act as energy generators, while bi-articular muscles distribute the energy across joints. In addition, estimates of muscular work have shown that energy transfer via bi-articular muscles contributes substantially to total work output during activities such as jumping and sprinting. The higher electromyography levels in combination with the greater extension ranges of motion at the hip and knee during the 4.5 m/s and 30% incline condition suggest enhanced energy generation by mono-articular extensors (gluteus maximus, vastus lateralis, and soleus) and energy transfer via bi-articular muscles (rectus femoris and medial gastrocnemius). This adaptation may be necessary to meet the rigorous demands of incline running at high speeds and grades. Also, the decrease in biceps femoris and medial hamstrings electromyography during stance provides evidence of antagonist inhibition-possibly allowing more net energy generation during these extreme conditions.
In summary, incline sprint training at 30% grade and 4.5 m/s elicited considerably greater electromyography activity in several muscles of the lower extremity during stance compared to similar level running conditions. The kinematic and electromyography data not only suggest higher forces and energy generation, but also indicate the feasibility that energy transport via bi-articular muscles may be enhanced in this extreme locomotion condition. As a training tool, high speed incline running is effective in increasing the activity levels in some, but not all lower extremity muscles.
Run The Planet thanks the American Society of Biomechanics (www.asb-biomech.org) for the permission to reprint the article "Muscular Coordination during Incline and Level Treadmill Running" by S.C. Swanson (Orthopedic Biomechanics Institute, Salt Lake City, Usa/Utah; Department of Exercise Science, University of Massachusetts, Amherst, Usa/Massachusetts), J.P. Frappier (Red River Valley Sports Medicine Institute, Fargo, Usa/North Dakota), and G.E. Caldwell (Department of Exercise Science, University of Massachusetts, Amherst, Usa/Massachusetts). The purpose of the American Society of Biomechanics is to provide a forum for the exchange of information and ideas among researchers in biomechanics as the study of the structure and function of biological systems using the methods of mechanics. This study was presented at the North American Congress on Biomechanics (University of Waterloo, Canada/Ontario; August 14-18, 1998) and was supported by Acceleration Products, Inc., Fargo (Usa/North Dakota). The expert technical assistance of Saunders Whittlesey is gratefully acknowledged. The text has been slightly adapted for a better readability.