Martin has previously expressed concern about some Comcast network practices, specifically that the company did not disclose more to customers and application developers about the way it manages traffic on its network.
Subsequently last month, Comcast announced it would change the way it manages its network and cooperate with BitTorrent and other critics to resolve the dispute. Comcast also said it would partner with a second file-sharing company and help create a "bill of rights" for consumers and Internet service providers.
Comcast, which has more than 13 million broadband subscribers, has denied impairing some applications and has said it merely managed the system to deal with network congestion for the good of all users.
In his prepared testimony for Tuesday's hearing, Martin said that "based on the testimony we have so far, some users were not able to upload anything they wanted and were unable to fully use certain file-sharing software from peer-to-peer networks."
Martin said the equipment Comcast used to delay traffic "is typically deployed over a wider geographic or system area and would therefore have impacted numerous nodes within a system simultaneously."
"It appears that this equipment blocks the uploads of at least a large portion of subscribers in that part of the network, regardless of the actual levels of congestion at that particular time," Martin said in his testimony.
The dispute over so-called network neutrality pits open-Internet advocates against some service providers such as Comcast, which say they need to take reasonable steps to manage traffic on their networks.
The head of the cable industry's chief trade group also testified at the hearing, telling lawmakers that concerns of network neutrality advocates are "misplaced."
Kyle McSlarrow, head of the National Cable & Telecommunications Association, said companies should be allowed to manage their networks as they see fit to alleviate congestion and combat illegal file-sharing.
McSlarrow said putting every network management technique up for scrutiny "would severely hamper the ability of network providers to ensure high-quality and reliable Internet access for their subscribers."