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Does Pain Reduce Peak Force Output?

What is the influence of pain on peak muscle force development? This study compared isometric deadlift strength and muscle excitation in individuals experiencing acute, non-specific low back pain with asymptomatic controls.

The researchers looked at the potential influence of bar type (conventional vs. hexagonal) and perceived self-confidence and safety. The study included 35 resistance-trained adults between 18 and 35 years old (10 males with LBP, 6 females with LBP, 9 asymptomatic males, and 10 asymptomatic females). All of the participants engaged in ≥ two resistance training sessions per week over the previous year. Participants in the LBP group reported recent pain onset that was still present pain but scored ≤5/10 on the NPRS, ≤15/30 on the FABQ-PA, ≤34/66 on the FABQ-W, and ≤14/24 on the RMDQ.

For the deadlift, the barbells were fixated at 7.62 cm below the apex of the patella for each participant. This bar height was chosen through pilot testing with the goal of high recruitment levels at the hip and knee joints while minimizing the amount of lumbar flexion. They used the conventional deadlift technique (barbell shoulder width apart). After warming up and becoming familiar with the position, each participant completed three, five-second maximal isometric deadlifts with each barbell. They were instructed to pull “hard and fast” and were provided strong verbal encouragement. Both peak force and RFDpeak were normalized to body mass (N/kg and N/second/kg, respectively). The order of barbells used was randomized.

For the LBP group, pain scores ranged from 1–5 and averaged 2.00. There was no difference in the feeling of safety or confidence during the lifts and no difference in bar preference. More upper trapezius and vastus lateralis activity with the hex bar. No reduction in force output between the groups. The data suggests mild levels of pain may not inhibit force output.

Of note, this was a trained group. They may have been performing deadlifts despite experiencing pain and are used to the activity. The lack of fear and high levels of confidence are key. If you or a patient has mild pain but no fear during a movement, you may not need to address the pain (i.e., manual therapy or pain medication) to improve the exercise potential. This study did not, however, assess endurance and tolerance to high-volume exercise and we don't know if pain will include those performance measures.

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