Warm-up Activities and Their Influences on Neuromuscular and Functional Indices

Abstract

Introduction: Researchers show that a high intensity warm-up prior to an explosive event, can improve one's performance [Gullich and Schmidtbleicher, 1996]. Post activation potentiation (PAP) is cited as the reason for these increases in performance. It is thought that PAP causes an increase in Ca++ sensitivity within the actomyosin complex [Sweeney, Bowman, and Stull, 1993]. However, it is not known whether it is the warm-up phase occurring before or the intense activity phase of the entire pre-event protocol that causes the neuromuscular changes often cited as post activation potentiation. So, the purpose of this study was to examine neuromuscular and functional outcomes of post activation stimulation caused by distinct phases of voluntary muscular activation. Methods: This study employed two separate oneway repeated measures designs. The sessions were single leg leg extension (LE) and tendon tap reflex (TTR); characterized by performing the activity using a resistance equal to 40% 1repetition maximum (1RM) and the muscle activity recorded within the rectus femoris caused by 6 N force rapidly applied to the patellar tendon respectively. Dependent measures were average rectus femoris EMG (AEMG) during the LE session and AEMG and peak isometric force (PIF) produced during the 120-ms post stimulus period within the TTR session. Data from nine subjects (174.66 ± 10.54 cm; 76.22 ± 13.22 kg; 21.67 ± 1.58 yrs) was collected using Noraxon telemetered EMG hardware and a tensile calibrated load cell integrated by DataPac 2000 software. The EMG signal, from both sessions, was processed (passive demeaning and RMS smoothed (20-msec)). The processed AEMG and the raw PIF were then normalized to their baseline values. The warm-up phase during each session consisted of a series of submaximal high bar parallel back squats: 1 × 5 at 50% of 1RM, 1 × 5 at 65% of 1RM, 1 × 3 at 75% of 1RM, 1 × 1 at 90% of 1RM with a three minute rest interval between sets and a five minute rest interval separating the warm-up phase from the data collection. At the conclusion of the 5-minute rest interval, the subjects began the intense activity phase, which consisted of 5 × 1 at 90% 1-RM with three minutes rest in between sets and a five-minute rest interval at the conclusion of the squat activity. Data collection resumed at the conclusion of this rest interval. Results: Significance was found during the warm-up phase and the intense phase on AEMG compared to baseline during the TTR (P ≤ 0.10). No significant effect was found on the AEMG during the LE session for any phase. PIF was significantly different for the intense phase (P ≤ 0.10). Discussion: PAP can alter segmental reflexive activity via neuromuscular changes and increasing force production. Neuromuscular changes can occur within any type of warm-up activity. Our study confirms that PAP can occur in untrained as well as recreationally trained individuals. Other studies have confirmed that PAP can occur in elite athletes as well [Gullich and Schmidtbleicher, 1996]. Future studies may want to investigate if and how PAP can alter motor unit recruitment patterns.